My Personal Itinerary
Davos Atmosphere and Cryosphere Assembly 2013
Air, Ice & Process Interactions
An IUGG (IAMAS & IACS) Event
July 8-12, 2013
08. Jul. 2013
Aspen II
Session
10:15 - 11:45
C6.1a
Properties and variability of the mountain snow cover
10:15 - 10:30
1071
Do snow depth measurement at typical flat-field locations represent total snow at
catchment scale?
Thomas Grünewald1,2, Michael Lehning1,2
n.3 foto
WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland, 2Cryos,
Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
1
Area wide snow cover is important for many applications ranging from meteorological or
hydrological modelling to snow cover maps as source of information for avalanche
warning and winter tourism. Such maps are usually produced by interpolating point
measurements. Snow stations (flat-field stations) are commonly located in flat, sheltered
terrain with relatively homogeneous snow cover. It can be assumed that most flat-field
stations do not represent the snow cover of the surrounding area, especially in complex
terrain as present in mountain regions. In contrast to the complex terrain in the
surrounding, the snow cover at sheltered flat-field station is typically less affected by wind
erosion and redistribution of snow by avalanches. Actually, such locations can be
expected to be influenced by enhanced deposition of precipitation.
In this study we aim to quantify the representativeness of typical mountain flat-field sites.
We analyze several data sets consisting of high resolution, area-wide snow depth
measurements obtained by airborne laser scanning. From digital terrain models and
snow depth maps, potential flat-field locations are defined automatically by applying two
criteria: (i) mean slope of the area (circle with 20 m radius around the station location) <
10° and (ii) standard deviation of the snow depth in the circular area < 20 cm. We then
manually identify locations exposed to the wind and exclude them from the analysis. The
snow depths form the virtual flat-fields are then compared to the mean snow depth of the
immediate vicinity of the flat field which is defined by circles with a rising area (radius 20
to 400 m) and to the catchment mean. The investigation shows that the vast majority of
stations clearly overestimate the mean snow depth of their vicinity. However, already
averaging the local measurements over increasing radiuses (up to 400 m) significantly
reduces this bias.
10:30 - 10:45
n. 7 foto
937
Observing the temporal and spatial variability of a mountain snow cover with a network of
individual snow monitoring sensors
Stefan Pohl1, Jakob Garvelmann1, Markus Weiler1
Institute of Hydrology, University of Freiburg, Freiburg, Germany
1
Topography and vegetation are considered dominant factors affecting the small-scale
spatial and temporal variability of mountain snow covers. Accurate knowledge of these
influences along with high resolution meteorological forcing data is crucial for any
distributed modelling of the spatio-temporal snow cover evolution. While many innovative
remote sensing techniques provide excellent data on the spatial variability of snow cover,
their temporal resolution in particular with regard to meteorological forcing data is often
lacking.
The study presented employs a network consisting of numerous standalone snow
monitoring stations that continuously monitor snow depth and the most important
meteorological variables needed to calculate a full (snow) surface energy balance. Over
100 of these stations were deployed over two winters in three meso-scale (< 150 km²)
basins in the Black Forest, a foothills type mountain region in Southern Germany.
Deployment locations were chosen to cover all relevant topographic situations and all
major land-cover types (open fields, deciduous and coniferous forests) typical for the
study area. Data showed that elevation and vegetation cover accounted for over 70% of
the spatial variability found in the snow depth and snow water equivalent (SWE). The
remaining variability could be attributed mainly to exposure, which only seemed to be
relevant for open locations, and the influence of the surrounding topography due to its
sheltering effects. The continuous nature of the measurements also made it possible to
look at the development of the strength of the relationships between SWE and, for
example, elevation throughout the winter. Furthermore, the recorded meteorological
variables provide an insight into the modifying effects of topography and different types of
vegetation on the individual snowmelt energy balance terms. The results of this study
should be very helpful for improving model algorithms aimed at modeling the temporal
and spatial variability in the evolution of a mountain snow cover.
10:45 - 11:07
969
n. 1 foto
per albedo
Airborne and ground-based LiDAR observations of seasonal mountain snow properties
Jeffrey Deems1,2, David C. Finnegan3, Adam L. LeWinter3,4, Eli J. Deeb3, Thomas H.
Painter5, Ananda Fowler6
National Snow and Ice Data Center, Boulder, United States, 2NOAA Western Water
Assessment, Boulder, United States, 3US Army Corps of Engineers Cold Regions
Research and Engineering Laboratory, Hanover, United States, 4University of Northern
Colorado, Greeley, United States, 5NASA Jet Propulsion Laboratory, Pasadena, United
States, 6Riegl Laser Measurement Systems GmbH, Horn, Austria
1
Manual field measurement of mountain snowpack properties is time-consuming and
subject to terrain constraints, leading to difficulties with repeatability and obtaining
adequate spatial resolution and coverage. Airborne and terrestrial laser scanning
provides surface elevation and reflectance measurement at high spatial resolution over
wide areas, and has recently seen an expansion of application to snow science interests.
This presentation provides an overview of a variety of lidar mapping and measurement
techniques in use for snow measurements by our extended team. We are using groundbased laser scans of snowpit faces for layer delineation and characterization. We
combine ground-based and airborne laser surveys for validation and bias correction of
basin-scale snow depth mapping efforts. Our in-situ ground-based system with
automated control allows monitoring of snowpack volume, accumulation, and melt, and
shows potential for observing precipitation and blowing snow mass flux. These varied
applications demonstrate the potential and value of lidar technology and techniques for
measuring and monitoring properties of the highly variable mountain snowpack.
11:07 - 11:29
637
n. 5 foto
Studies of the small-scale spatial variability of alpine snowfall and snow accumulation
using an X-band polarimetric radar
Danny Scipion1, Rebecca Mott2, Michael Lehning3, Alexis Berne1
Environmental Remote Sensing Lab., Ecole Polytechnique Fédérale de Lausanne EPFL,
Lausanne, Switzerland, 2Institute for Snow and Avalanche Research, Davos, Switzerland,
3
Laboratory of Cryospheric Sciences, Ecole Polytechnique Fédérale de Lausanne EPFL,
Lausanne, Switzerland
1
A mobile polarimetric X-band radar (MXPol) deployed in the vicinity of Davos
(Switzerland) collected high-resolution quantitative information on precipitation for the
winter seasons of 2009/2010 and 2010/2011. Local measurements of snow accumulation
were collected with Airborne Laser Scanning (ALS) at the Wannengrat area (Davos,
Switzerland) for the winters 2007/08 and 2008/09. The spatial distribution of snow
accumulation exhibits a strong inter-annual consistency that can be generalized over the
winters in the area. This unique configuration makes the comparison of the variability in
snowfall (as seen by the radar) and in snow accumulation (from laser scans) possible
over the diverse winter seasons.
The spatial variability, quantified by means of the variogram, is shown to be larger in
snow accumulation than in snowfall (at the seasonal scale). This indicates that other
factors (like wind and turbulence taking place close to the ground) induced by small-scale
topographic features govern the snow deposition and accumulation at the ground level in
mountainous areas. Further investigation of this question is done by dividing the radar
coverage into two disjoint domains at different elevations, roughness, and proximity to
the ground. The variability of snowfall appears consistently larger in the vicinity of the
ridge than far from the ground, which confirms the influence of the rugged topography on
snowfall. In addition, small-scale turbulence is stronger close to the surface where winds
are in direct contact with the terrain, as observed from normalized histograms of Doppler
spectral width. Finally, normalized variograms of Doppler radial velocity showed a more
organized structure at higher elevations. This corroborates the important role of smallscale topography in spatial distribution of snowfall/snow accumulation.
11:29 - 11:44
842
Implementation and evaluation of prognostic representations of the optical diameter of
snow in the detailed snowpack model SURFEX/ISBA-Crocus
n. 6 foto
Carlo Carmagnola1, Samuel Morin1, Matthieu Lafaysse1, Florent Domine2, Ghislain
Picard3, Laurent Arnaud3
Météo-France - CNRS, CNRM - GAME, CEN, St Martin d'Hères, France, 2Takuvik Joint
International Laboratory, CNRS and Université Laval, Québec, Canada, 3CNRS Université Joseph Fourier Grenoble, LGGE, Grenoble, France
1
Few snowpack models incorporate an explicit representation of metamorphism
processes. In the SURFEX/ISBA-Crocus multi-layer snow model, snow metamorphism is
implemented in a phenomenological way, through a set of equations describing the
evolution rate of the grain properties. Snow grains are characterized by their size and by
semi-empirical shape variables, dendricity and sphericity, which cannot be measured
easily in the field or linked to other relevant snow properties. The optical diameter (which
is, in contrast, a well-defined variable representing the geometric characteristics of a
porous medium) is then derived from those quantities in order to compute the NIR albedo
of snow.
Here we introduce an alternative approach, in which snow metamorphism within Crocus
model is now described by equations formulated in terms of the rate of change of two
state variables, sphericity and optical diameter. In other words, we replaced two of the
primary Crocus parameters (dendricity and size) with optical diameter, turning the latter
into a prognostic variable in the code. This new formulation makes it easier to implement
different parameterisations of the rate of increase of optical diameter, in addition to the
reformulation in terms of sphericity and optical diameter of the current metamorphism
laws.
These parameterizations were then evaluated by comparing them to field measurements.
Two instruments which retrieve optical diameter from infrared reflectance measurements
at 1310 nm, DUFISSS and ASSSAP, were used in May and June 2011 at Summit Camp
(Greenland) and during the 2011/12 winter season at Col de Porte (French Alps). During
these field campaigns, data were acquired with high vertical resolution (about 1 cm),
allowing to test the accuracy of the different dry metamorphism formulations.
Aspen II
Session
13:15 - 14:45
C6.1b
Properties and variability of the mountain snow cover
13:15 - 13:30
362
Snow cover variability in a small watershed in a temperate mountain range: the Central
Spanish Pyrenees
Jesús Revuelto1, Juan Ignacio López-Moreno1, Cesar Azorin-Molina1, Sergio M. VicenteSerrano1, Gonzalo Arguedas2
Department of Geoenvironmental Processes and Global Change, Pyrenean Institute of
Ecology (Spanish Research Council), Zaragoza, Spain, 2Geotechnical Engineering,
Cartography and Geosciences, Universidad Politécnica de Catalunya, Barcelona, Spain
1
Spatial distribution of snowpack exhibits a large variability in mountain terrain.
Understanding the main factors which control snow distribution is important for assessing
available water during the melting season and studying many ecological and
geomorphological processes in mountain areas.
In this study, a Terrestrial Laser Scanner (TLS) has been used with the aim of obtaining
Digital Terrain Models (DTM) of snow free and snow covered areas in a small watershed
of 55ha above 2000 m.a.s.l. in the Central Spanish Pyrenees. Thus, high resolution snow
thicknesses maps have been generated for several dates in the 2012 and 2013 snow
seasons. In addition, manual measurements of snow depth were taken within each
experimental campaign in order to assess the quality of snow thicknesses maps acquired
by the TLS. Furthermore, meteorological data are continuously recorded with an
automatic weather station (AWS) which provided valuable data for later analysis. The
study area has different orientations and its topography is varied enough for analyzing
the snowpack evolution in concavities, flat areas and convexities.
Once the accuracy of resulting maps has been validated as a function of measurement
distances, linear and non-linear regression models have been applied in order to relate
snow distribution with topography, wind exposure and shielding of the different basin
zones. This experimental study has enabled to get results on the main factors which
explain snow distribution in the catchment and to assess whether if the role of such
factors is constant in time or exhibits intraanual and interannual variability. New results
have highlighted the strong spatial variability of snowpack in the Central Spanish
Pyrenees. In particular, the snow redistribution by wind and exposure to solar radiation
exerts a key role in the snow accumulation in the basin. However, this impact is
subjected to large variations between the different analysed surveys.
13:30 - 13:52
108
Persistence in intra-annual snow depth distribution. Part I: measurements and
topographic control
Michael W. Schirmer1,2, Michael Lehning2, Vanessa Wirz2,3
n. 1 foto
Applied Snow and Avalanche Research, University of Calgary, Calgary, Canada, 2WSL
Institute for Snow and Avalanche Research SLF, Davos, Switzerland, 3University of
Zurich, Zurich, Switzerland
1
Terrestrial and Airborne Laser Scanning (TLS and ALS) techniques have only recently
developed to the point where they allow wide-area measurements of snow distribution in
varying terrain. In this paper we present multiple TLS measurements showing the snow
depth development for a series of precipitation events. We observe that the pattern of
maximum accumulation is similar for the two years presented here (correlation up to
r=0.97). Storms arriving from the Northwest show persistent snow depth distributions and
contribute most to the final accumulation pattern. Snow depth patterns of maximum
accumulation for the two years are more similar than the distribution created by any two
pairs of individual storms. Based on the strong link between accumulation patterns and
terrain, we investigated the ability of a model based on terrain and wind direction to
predict accumulation patterns. This approach of (Winstral et al., 2002), which describes
wind exposure and shelter, was able to predict the general accumulation pattern over
scales of slopes but failed to match observed variance. Furthermore, a high sensitivity to
the local wind direction was demonstrated. We suggest that Winstral´s model could form
a useful tool for application from hydrology and avalanche risk assessment to glaciology.
13:52 - 14:14
471
Analysis of multi-annual end-of-season snow accumulation patterns from LiDAR data
Kay Helfricht1,2, Katrin Schneider1, Johannes Schöber1,3, Michael Kuhn2
n. 3 foto
x Alplinks
alpS Centre for Climate Change Adaptation Technologies, Innsbruck, Austria, 2Institute
of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria, 3Institute of
Geography, University of Innsbruck, Innsbruck, Austria
1
Spatially distributed modelling of the mountain snow cover is of importance for a realistic
prediction of runoff generation from melt water. However, data of snow depths is mostly
available only on the point scale for model calibration and validation. Information on the
spatial distribution of snow depths is sparse. Surface elevation changes derived from
LiDAR can be interpreted as snow depth to analyse snow accumulation patterns in
complex alpine topography. Airborne Laser Scanning (ALS) provides this inormation on
the catchment scale with a high resolution of less than 1 meter. The question is whether
and where this distribution is representative for the mean spatial distribution of the snow
cover in these catchments on a multi-annual time scale. For a small glacierized
catchment (approx. 36 km²) in the Ötztal Alps (Tirol, Austria) maps of the spatial
distribution of surface elevation changes are available for five accumulation seasons.
These maps where analysed regarding the multi-annual persistence and the variability of
the snow accumulation patterns. The study aims to evaluate the validity of zones with
similar characteristics. In the five accumulation seasons under consideration, snow
covered area is less variable than mean annual snow depth. In the catchment areas next
to the mountain ridges snow depth distribution is controlled by wind exposure and slope.
In the lower elevation zones energy balance is responsible for differing snow depths,
which can be related to the topographic controls elevation and aspect. An increased
snow accumulation compared to unglacierized areas is obvious on glacier surfaces in all
five years. The multi-annual analysis reveals typical release and accumulation zones of
avalanches. Likewise, singular avalanche events which do not occur regularly can be
detected. Areas influenced by wind redistribution can be delineated from typical
accumulation patterns on the glaciers.
14:14 - 14:29
233
Understanding snow accumulation patterns in an highly glacierized alpine catchment
Ilaria Clemenzi1, Francesca Pellicciotti1, Paolo Burlando1
Institute of Environmental Engineering, ETH Zurich, Zurich, Switzerland
1
Snow depth variability is determined by multiple processes acting at different spatial and
temporal scales (precipitation deposition, transports by wind and redistribution due to
avalanches). A way to explore snow spatial distribution is to use fractal analysis
determining fractal dimensions and scale breaks. Numerous studies have used this
approach to characterise snow distribution at a variety of spatial scales and temporal
resolutions. Several have used this approach to identify the inter-seasonal consistency of
snow accumulation patterns or to compare patterns between different basins. Only few
have looked at intra-seasonal variability and fewer have focused on snow depth scaling
properties in glacierized catchments. We investigate the spatial and inter-seasonal
variability of snow accumulation patterns over Haut Glacier d'Arolla in the Swiss Alps
during two accumulation seasons (2006-2007 and 2010-2011). The focus of our work is
whether the snow depth distribution at the end of the accumulation season is consistent
between the two seasons. We use DEMs generated by high resolution helicopter-borne
LiDAR-data and calculate snow accumulation as the difference between them. We
investigate the spatial structure of snow depth in subareas in the upper basin and on the
tongue for the two years, calculate the omnidirectional and directional variograms and
describe the snow depth scaling behaviour through the fractal dimension. Interannual
consistency in the accumulation patterns can be observed between the two years.
Further, we find a distinct behaviour on the tongue and in the upper basin: subareas on
the tongue are characterized by a difference in the fractal dimension for the two
perpendicular directions of North-South and East-West. This is not evident in the upper
area. We interpret this as the result of the exposition of these areas to the prevailing wind
direction observed during the considered period, which result particularly influenced by
the topographic features of the catchment.
14:29 - 14:44
n. 1 foto
1252
High-resolution modeling of wind-induced snow transport using a fully coupled
snowpack/atmosphere model
Vincent Vionnet1,2, Eric Martin2, Valery Masson2, Gilbert Guyomarc'h3, Florence Naaim
Bouvet4, Alexander Prokop5, Yves Durand3, Christine Lac2
Meteorological Research Division, Environment Canada, Dorval, Canada, 2CNRMGAME (Météo-France-CNRS), Toulouse, France, 3CNRM-GAME/CEN MétéoFrance/CNRS, Saint Martin d'Heres, France, 4IRSTEA, UR ETGR Erosion Torrentielle
Neige et Avalanches, Saint Martin d'Heres, France, 5Institue of Mountain Risk
Engineering, BOKU University, Vienna, Austria
1
In alpine regions, blowing snow events strongly influence the spatio-temporal evolution of
the snow cover throughout the winter season. To gain understanding on the complex
processes that drive the redistribution of snow during such events, we used the recently
developed simulation platform Meso-NH/Crocus. This coupled system consists in the
detailed snowpack model Crocus and the atmospheric model Meso-NH. MesoNH/Crocus simulates snow transport in saltation and in turbulent suspension and
includes the sublimation of suspended snow particles.
We present the first detailed evaluation of the model against data collected around the
experimental site of Col du Lac Blanc (2720 m a.s.l., French Alps). For this purpose, a
blowing snow event without concurrent snowfall has been selected and simulated.
Results show that the model captures the main structures of atmospheric flow in alpine
terrain, the vertical profile of wind speed and the snow particles fluxes near the surface.
However, the horizontal resolution of 50 m is found to be insufficient to simulate the
location of areas of snow erosion and deposition observed by terrestrial laser scanning.
When activated, blowing snow sublimation causes a reduction in deposition of 5.3 %.
Total sublimation (surface + blowing snow) is three times higher than surface sublimation
in a simulation neglecting blowing snow sublimation.
09. Jul. 2013
Aspen II
Session
08:15 - 09:45
C6.1/C6.4
Properties and variability of the mountain snow cover / Avalanche protection,
measures and hazard mapping
08:15 - 08:30
845
Simulating melt crust and ice lens formation in a physically based snowpack model
Nander Wever1, Charles Fierz1, Michael Lehning1,2
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland,
CRYOS, School of Architecture, Civil and Environmental Engineering, École
Polytechnique Fédéral de Lausanne, Lausanne, Switzerland
1
2
Water flow in a natural snow cover is generally a complex process because of the
strongly stratified and changing structure of the snowpack. Important differences in, for
example, density and grain size between layers cause sometimes very sharp transitions
in hydraulic properties. Experiments have shown that water accumulating on capillary
barriers in the snow cover can reduce its strength and thereby favour wet snow
avalanche formation. Refreezing at capillary barriers within the snow cover leads to the
formation of ice lenses or ice crusts, which favors the development of large-grained weak
layers (facets and depth hoar). During the melt season, crusts and large grains strongly
influence the vertical water flow in snow. Blocking of the vertical flow can lead to lateral
flow or to delayed arrival of melt water at the bottom of the snowpack.
We extended the model SNOWPACK with a solver for 1D unsaturated flow (Richards
Equation), which considerably improved melt water runoff estimations. Here we show
that Richards Equation is also capable of reproducing capillary barriers at interfaces
between snow layers of differing properties; a real modelling challenge. Moreover, the
method to determine the hydraulic conductivity at the interface nodes between snow
layers plays a major role in the behaviour of simulated water flow. Comparing the
arithmetic with the so-called Darcian averaging approach for internodal hydraulic
conductivity, we show that the latter is able to reproduce important accumulation of liquid
water at interfaces within the snowpack. Refreezing of this water leads to layers that can
be considered crusts or ice lenses, with higher densities than layers above and below.
We compare the simulation results with observed snow profiles. The ability of
SNOWPACK to reproduce melt-freeze crusts and ice lenses will be helpful in future
studies on travel times of water through the snowpack or assessing snowpack stability.
08:30 - 08:52
429
Avalanche risk zoning as a total loss minimisation problem
Nicolas Eckert1, Eric Parent2, Mohamed Naaim1, Philomene Favier1
n. 2 foto
IRSTEA, Saint Martin d'Heres, France, 2AgroParisTech/INRA, UMR 518 Math. Info.
Appli, Paris, France
1
Using high return period avalanches as reference events has the advantage of using the
same thresholds than for other hazards (e.g. 100 years), but severe drawbacks. First, the
reference event considered remains undefined from the perspective of the runout
pressure joint distribution. Second, it does not explicitly take into account the elements at
risk, possibly leading to inacceptable risk levels. Hence, the individual risk concept has
been recently introduced in the engineering practice and an optimal design framework
based on decision theory has been proposed for avalanche countermeasures. The aim of
this work is to bridge these attempts, showing how avalanche risk zoning can result from
the minimization of total losses, leading the best compromise between expected fatalities
and urbanization constraints with regards to the stake holder's behavior against risk. It
requires the determination of the statistical values of human life and of urbanized areas.
The first one can be elicited for each case study from the stake holder's choices. The
second one can be roughly approximated from the total economic value of a mountain
community.
First, the simplifying assumption of a constant death probability conditional to the
avalanche hit is made. With a simplified peak over threshold model, this leads analytical
solutions, i.e. high and moderate risk limits as explicit optimal functions of model
parameters under both classical and Bayesian paradigms. Second, it is shown that
additional decisional variables such as a dam height can be easily accounted for,
illustrating that the proposed framework is able to handle the main challenges of
avalanche long term forecasting in a consistent manner. Finally, death probabilities
functions of the position are tested, as a first step before a full numerical implementation.
This all may have a great impact of hazard mitigation theory and practices.
08:52 - 09:14
1179
LiDAR mapping of snow depth in avalanche starting zones in Iceland for assessing
avalanche hazard and design of supporting structures
Tómas Jóhannesson1
Icelandic Meteorological Office, Reykjavík, Iceland
1
Snow avalanches threaten several coastal villages in northwestern, northern and eastern
Iceland. An effort for assessing avalanche risk and construct avalanche protection
measures was initiated after two catastrophic avalanches killed 34 persons in the villages
Flateyri and Súðavík in 1995. Snow depth in avalanche starting zones in Iceland is
greatly affected by redistribution of snow by wind in the maritime climate of the country.
Accurate information about the spatial distribution of snow depth is therefore essential for
hazard zoning and for optimal design of avalanche supporting structures. Aerial lidar
surveying of snow-covered mountainsides in May 2008 and of the same areas free of
snow in the fall of 2008 and 2009 have been used to construct snow depth maps for eight
mountainsides above avalanche-threatened villages in Iceland. Validation measurements
by manual probing of snow depth were carried out on the same day in one of the areas,
confirming excellent accuracy of the derived snow depth to within ~10 cm. The snow
depth maps clearly show the preferential accumulation of snow in depressions and on
the lee side in gullies. The maps also shows interesting formations of thick snow drifts at
other locations that can be 5-10 m thick and >100 m long and seem to be caused by
wind flowing up steep gullies or around bedrock protuberances. The snow depth maps
have proved useful for detailed determination of structure heights in the design of
supporting structures in the Hafnarfjall mountainside above the village of Siglufjörður in
Northern Iceland.
09:14 - 09:29
197
X info!
Exploring the snow lateral variability within a 20 m snow trench at Concordia Station,
East Antarctica
Fabiano Monti1, Christine D. Groot Zwaaftink1, Martin Schneebeli1, Charles Fierz1,
Giovanni Macelloni2, Anselmo Cagnati3
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland,
Institute of Applied Physics “Nello Carrara”, Sesto Fiorentino, Italy, 3ARPAV CVA,
Arabba di Livinallongo, Italy
1
2
Although the East Antarctic plateau has few significant topographic features, snow
stratigraphy on the first meters is strongly heterogeneous in space. This variability is
mainly caused by wind, which affects snow surface features such as zastrugi and dunes,
dominating snow deposition and its properties (snow density, grain size, and grain
shape).
This heterogeneity of the snow cover prevents an easy comparison between snow
profiles both in space and time, hindering interpretation of remote sensing data (e.g.
microwave measurements). Moreover, it challenges our ability to develop a better
understanding of snow cover development based solely on punctual snow profile
records. Indeed, changes in snow stratigraphy due to either temporal evolution or spatial
variability are hardly distinguishable.
Snow cover simulations could help gaining insight in the snow cover development.
However, as profile matching layer by layer is difficult, model validation is currently
limited to the surface energy balance and snow temperatures.
In this study, we explore whether we could obtain more insight through a series of
adjacent snow profiles to characterize the spatial variability. Then we might better tackle
the temporal effect on the evolution of the snow cover. During the 2012-2013 summer
campaign, a snow trench 20 m long and 1.80 m deep was dug near Concordia Station at
Dome C. In addition to three full snow profiles, we recorded snow stratigraphy with
infrared pictures. Our observations confirm the limited lateral continuity of snow layers
and the strong influence of the wind. Layers within the 3 profiles could not be matched,
but in each profile, similar stratigraphic patterns can be identified.
We investigate the effect of snow metamorphism and wind on the formation of these
patterns and explore whether snow cover models can assist in understanding those,
especially for winter periods when manual observations are missing.
09:29 - 09:44
X info!
1143
Improvements in the design of snow avalanche impact resisting buildings from backanalyses on real events
Valerio De Biagi1, Bernardino Chiaia1, Barbara Frigo1
Politecnico di Torino, Torino, Italy
1
Damages on real scale structures give an effective possibility to engineers and
researchers to understand the response of constructions to the actions impressed by
natural phenomena. The damages caused by the extreme snow avalanche of Les
Thoules in Aosta Valley on December 2008 are analysed and the main features of the
response of the totally and partially collapsed structures to snow flow are highlighted.
Collapse mechanisms are emphasized and their limit capacity is computed.
The results of the back-analysis are then turned into prescriptions and indications for the
design of buildings under snow avalanche hazard. Pressure distribution on corners as
well as structural detailing play a fundamental role in the overall robustness of the
construction. An example on a new house is presented.
Aspen II
Session
10:15 - 11:45
C6.3
Avalanche flow dynamics
10:15 - 10:30
187
Deducing the size and velocity of avalanches from radar, seismic and infrasound data at
Vallée de la Sionne
n. 1 foto
Cristina Perez Guillen1, Betty Sovilla2, James N. McElwaine2, Emma Suriñach3
X Nathalie
Rumore della
frattura non ai fini
previsionali.
Geodinámica y Geofísica, University of Barcelona, Barcelona, Spain, 2Research Unit
Avalanches and Prevention WSL Institute for Snow and Avalanche Research SLF,
Davos, Switzerland, 3University of Barcelona, Barcelona, Spain
1
Snow avalanches are extended sources of seismic and infrasonic waves. Recent studies
have shown that the interaction between the dense core of an avalanche and the basal
surface is the main source of the seismic signal, whereas the suspended powder cloud
and the dilute layer are the main sources of infrasound. These sensors thus give
complementary information about the characteristics of an avalanche and can, in theory,
be used to deduce avalanche speed, location and size as functions of time. In practice
however this is very difficult because accurate models are needed for source generation
and wave propagation and these models must be validated. We compare the seismic
and infrasound data with FMCW radars and the GEODAR radar. FMCW radars are
installed at three locations and provide high frequency measurements of the internal
profile of the avalanche as it flows over the sensor revealing erosion, deposition and the
flow regime. The GEODAR radar is a phased array system located at the bunker on the
counter slope. It can track the avalanche over the whole slope with high resolution, and
gives information on avalanche position, velocity and size. The infrasound sensor is also
located at the bunker and the three seismic sensors are spaced along the slope.
We correlate the magnitude of the avalanche dilute layer and its front velocity with the
intensity of the infrasound signal. Furthermore, we compare avalanche length, height and
flow regimes with the amplitude, duration and frequency content of the seismic signal.
This comparison allows the calculation of seismic and infrasound parameters (length of
the signals, amplitude and energy) that can be useful to characterize type, size and path
of snow avalanches. Moreover, we discuss the feasibility of deducing the avalanche
location from the seismic and infrasound data by comparison with GEODAR data.
10:30 - 10:45
1040
Measuring the thermal balance of a snow avalanche
Walter Steinkogler1,2, Betty Sovilla1, Tobias Jonas1, Michael Lehning1,2
SLF, Davos Dorf, Switzerland, 2CRYOS, EPFL, Lausanne, Switzerland
1
n. 1 foto
Avalanches can exhibit many different flow regimes from powder clouds to slush flows.
Flow regimes are largely controlled by the properties of the snow released and entrained
along the path. Recent investigations showed the temperature of the moving snow to be
one of the most important factors controlling the granulometry and thus the mobility of the
flow. The temperature of an avalanche is mainly determined by the temperature of the
released and entrained snow but also increases by frictional and collisional processes
with time.
The aim of this study is to calculate the thermal balance of an avalanche using infrared
thermography technology. For this work an avalanche was artificially released at the
Flüelapass (2383 m.a.s.l.) close to Davos, Switzerland. A thermal imaging camera was
used to assess the temperature before, during and just after the avalanche with a high
spatial resolution. Snow profiles along the avalanche track and terrestrial laser scans,
conducted before and after the avalanche, allowed to quantify the temperature of the
eroded snow layers. This data set allows for the first time to calculate an entire thermal
balance, from release to deposition, of an avalanche. The comparison between the
measured temperature of the entrained snow layers and the temperature of the
deposition allowed to draw conclusions whether the main contribution to the warming of
the snow in the avalanche arose from friction or entrainment of relatively warmer snow.
Our results allow for a more comprehensive understanding of snow temperatures in
avalanche flow and their consequence on flow regimes. This information can directly be
used to enhance the performance of avalanche dynamics models and are thus of great
interest for practitioners. We further discuss advantages and limitations of the presented
method and the technologies.
10:45 - 11:15
856
Self-consistent approximations to the dynamics of basal entrainment in snow avalanches
Dieter Issler1, Tómas Jóhannesson2
Natural Hazards Division, Norwegian Geotechnical Institute, Oslo, Norway, 2Icelandic
Meteorological Office, Reykjavík, Iceland
1
Observations indicate that the highest erosion rates in snow avalanches usually occur at
the very front of the flow. However, despite lower erosion rates, basal entrainment may
give a similar contribution to the mass balance due to the extended area over which it
occurs. For physical reasons, the erosion rate must be determined uniquely by the
properties of the snow-cover and the dynamic characteristics of the flow. In contrast,
entrainment models typically contain adjustable parameters whose relation to the snowcover and flow characteristics remains elusive.
In order to shed some light on this question, a quasi-stationary eroding flow over a
perfectly brittle bed was studied in the infinite-slope approximation. The brittleness
assumption implies that the shear stress must exceed a critical value, but no work is
expended to break the interparticle bonds. A key point is that the dynamics keeps the
bed shear stress locked at the critical shear stress value as long as erosion takes place.
For a Bingham visco-plastic flow rheology, analytical solutions for the velocity profile can
be found and the entrainment rate uniquely determined from a transcendental equation,
without adjustable parameters beyond the measurable material properties. For more
complicated rheologies, unique solutions can be found numerically.
The approximation of an infinitely long, quasi-stationary flow can be removed at the
expense of analytical solvability by implementing the model in an Eulerian quasi-3D flow
code. The non-equilibrium erosion rate is approximated by the equilibrium erosion rate at
a different slope angle that gives the same depth-averaged flow velocity. As an
alternative to the computationally expensive solution of a transcendental equation for
every grid point and time step, the use of the velocity profile of a corresponding nonentraining flow has also been studied. Selected simulations serve to illustrate the
behavior of the model.
11:30 - 11:45
953
Development, refinement and application of a new evaluation and comparison method for
computational snow avalanche simulation
Jan-Thomas Fischer1, Reinhard Fromm1, Peter Gauer2, Betty Sovilla3, Walter
Steinkogler3, Matthias Granig4, Marc Christen3
Institute of Natural Hazards, Austrian Research Centre for Forests, BFW, Innsbruck,
Austria, 2Norwegian Geotechnical Institute - NGI, Oslo, Norway, 3WSL Institute for Snow
and Avalanche Research SLF, Davos, Switzerland, 4Austrian Service for Torrent and
Avalanche Control - Centre for Snow and Avalanches, Schwaz, Austria
1
This contribution summarizes the results and further developments of the Automated
Indicator based Model Evaluation and Comparison (AIMEC). Computational snow
avalanche simulation has gained importance in hazard mapping and mitigation planning.
The simulations are based on depth averaged models operating in three-dimensional
terrain, providing results such as flow velocity, depth and pressure. Complexity and large
amount of results make an objective comparison of a high number of simulation runs
challenging and difficult to interpret. Here we present applications of AIMEC, which has
been introduced to: (1) effectively handle large amounts of simulation results, (2) provide
mathematical definitions representing main avalanche features in a clear and
comprehensive way, (3) provide the basis to evaluate deterministic simulation results by
means of probabilistic methods. Key point of this method is a coordinate transformation
in an avalanche path dependent system, which allows to introduce new metrics, the so
called indicators. The indicators allow to directly analyze large samples of simulation runs
with respect to e.g., the avalanche run out or destructiveness. Two examples show how
to (1) improve model calibration by evaluating simulation results with field data and (2)
compare the results of different simulation software, highlighting the influence of the
different model implementations. The new method is helpful for the interpretation of
avalanche simulations with a broad applicability in model evaluation, comparison as well
as model calibration.
13:15 - 14:45
Aspen II
Session
C6.2a
Avalanche formation and forecasting
13:15 - 13:30
1216
On the failure behaviour of depth hoar
Ingrid Reiweger1, Jürg Schweizer1
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
1
Understanding the failure behaviour of weak snow layers is essential for modelling and
predicting dry-snow slab avalanches. We therefore performed laboratory experiments
with snow samples containing a weak layer consisting of depth hoar. During these
experiments the samples were loaded until fracture. We measured the deformation at the
side of the samples with a high-speed camera. The fracture process within the weak
layer could thus be studied in detail. We found a fracture in shear immediately followed
by a collapse of the weak layer. In addition, we measured acoustic emissions to find an
indication of imminent failure. According to our experiments the most promising acoustic
parameter for predicting snow failure seems to be the exponent β of the cumulative sizefrequency distribution ('survival curve') of event energy. In a stable state β takes a
constant value of about three. At the occurrence of instabilities the β curve deviates from
the constant behaviour and exhibits distinct 'dips', indicating that the power law behaviour
of the distribution is not fulfilled anymore. Studying the temporal evolution of the
exponent β could therefore provide useful information on snowpack stability.
13:30 - 13:45
934
Using particle tracking velocimetry to measure the mechanical properties of snow
relevant for dry-snow slab avalanche release
Alec van Herwijnen1, Ned Bair2, Karl Birkeland3, Benjamin Reuter1, Ron Simenhois4,
Bruce Jamieson5, Jürg Schweizer1
WSL – Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, 2US
Army Corps of Engineers Cold Regions Research and Engineering Laboratory, Hanover,
United States, 3USDA Forest Service National Avalanche Center, Bozeman, United
States, 4Coeur Alaska, Juneau, United States, 5University of Calgary, Calgary, Canada
1
Particle tracking velocimetry (PTV) is a widely used measurement technique to determine
the displacement and velocity of particles from video recordings. The technique has the
advantage of being largely nonintrusive and being capable of simultaneously measuring
the state of deformation over an entire cross section of the sample. PTV has been used
to study the deformation and fracture of snow in field and laboratory experiments since
the mid 1990s. While initial studies focused mainly on documenting weak layer collapse
and fracture propagation velocities, recent advances now allow the determination of
essential mechanical properties relevant to snow slab avalanche release. On a more
practical side, PTV has also been used to study the mechanics of various stability tests,
such as the Propagation Saw Test or the Extended Column Test, highlighting similarities
as well as certain limitations of these tests. We will give an overview of field experiments
performed in Canada, USA and Switzerland over the last 10 years, with a particular view
on relating the material properties of snow to commonly observed snow cover
characteristics, such as snow density and grain type. While PTV has improved our
understanding of the fundamental processes involved in snow fracture, we will also
highlight areas which thus far have received little attention.
13:45 - 14:07
499
Segmentation of snow grains from microtomographic data to derive the specific grain
contact area as a mechanical indicator
Pascal Hagenmuller1, Xi Wang2,3, Frederic Flin2, Guillaume Chambon1, Mohamed Naaim1
UR ETGR, Irstea, Centre de Grenoble, Saint Martin d'Hères, France, 2CEN, MétéoFrance, CNRS, Saint Martin d'Hères, France, 3LIRIS, Université de Lyon, CNRS,
Villeurbanne, France
1
The concept of snow grain is commonly used in the snow community, either in situ to
identify the type of snow or in numerical modeling to reproduce the physical and
mechanical behavior of the snowpack. The specific grain contact area (SGCA) has long
been believed to be a relevant mechanical indicator. Similarly to the specific surface area
which measures the surface of exchange with the environment, SGCA measures the
surface of force exchange between grains.
The snow grains can be studied using 2D sections or images of individual grains taken
from the snowpack. Nevertheless, this reduced representation of microstructure fails to
reproduce the 3D-connectivity between grains.
The 3D microstructure of snow is available via X-ray micro-tomography. However, usual
decomposition algorithms have difficulties to separate individual grains from 3D
assemblies of particles with various shapes and contact topology. Recently, «curvaturebased» segmentation algorithms, where the necks are defined as negative Gaussian
curvature zones, have shown promising results on 3D snow images. Nevertheless, the
way in which the surface information (negative curvature) is spread into the volume
(Voronoi diagram; fire front´s propagation) yields twisted contact surfaces with overestimated areas. We propose a new approach that propagates the grain seeds obtained
by the curvature-based algorithm while minimizing the overall grain contact area. This
criterion is relevant for further mechanical considerations where the "weakest necks" are
determinant.
This algorithm is successfully applied to 3D snow images and compared to the curvaturebased algorithm. A similar number of grains is detected but the computed SGCA is
significantly lower with our approach. Moreover, the minimization of the contact area
makes our approach robust, in particular when over-segmentation occurs in the
curvature-based algorithm. Finally, our algorithm is used to derive the evolution of the
SGCA with metamorphism.
14:07 - 14:29
212
Snow avalanches genetic types derived from spatial modeling of snowpack structural
instability on Olympic slopes 2014, Western Caucasus, Russia
N. 1 foto
LAVORO
INCREDIBILE!!
Elena Klimenko1
The Laboratory of Snow Avalanches and Debris Flows, Lomonosov Moscow State
University, Moscow, Russian Federation
1
PARTE DELLA
TESI DI DOTT.
DI FABIANO
(RICHIESTA)
->
Snow avalanche formation is a result of complex interaction of variable in time,
heterogeneous, stratified snowpack and relief of underlying surface. Therefore,
avalanche release should be prepared in advance inside snowpack being a result of
unstable layer/interface presence within snow structure. It comes out with an idea of
“structural instability” which was previously referred just to slabs. Meanwhile wide variety
of genetic types of snow avalanches was described in the field which are much less
considered nowadays.
In our work we extended the idea of “structural instability” linking physical conditions
within snowpack, possible mechanisms of failure and genetic types of avalanches. As a
result came out with a new classification scheme which can be used to assess the
readiness of snowpack to form an avalanche of any genetic type. The overall aim of our
research is to model spatially and assess structural snow stability with a reference to a
genetic type of possible avalanches.
We introduced a complex method which allows to obtain spatial patterns of unstable
snow structures distribution at avalanche sites as output. It includes detailed
morphological analysis of DTM, meteorological data recalculation, physical modeling of
snowpack, snow stability assessment using our classification scheme, statistical analysis
of modeling results.
We applied our method to model snow stability in Rosa Khutor ski resort, Western
Caucasus during the winter 2011-12. The resort is going to receive the Olympics 2014
that increases the relevance of our research. We used Swiss model Snowpack to
simulate snow cover evolution. Modeling results were verified with snow pitting data and
avalanche observations. In every site where avalanche descends took place extensive
unstable zones had been modeled. 90% of registered avalanches had the same genetic
type as we predicted with our classification scheme.
Aspen II
Session
16:15 - 17:45
C6.2b
Avalanche formation and forecasting
16:15 - 16:30
76
Influence of weak layer heterogeneity on snowpack stability
Gaume Johan1, Chambon Guillaume1, Eckert Nicolas1, Naaim Mohamed1
IRSTEA, Grenoble, France
1
The spatial variability of snow mechanical properties has an important impact on
snowpack stability and thus on avalanche formation. In this study, a mechanically--based
statistical model of the slab--weak layer (w.l.) system relying on random finite element
simulations is used to investigate snowpack stability and avalanche release probability.
This model accounts, in particular, for the spatial varibility of w.l. mechanical properties
and stress redistributions by elasticity of the slab. We show how avalanche release
probability can be computed from release depth distributions which allow us to study the
influence of w.l. heterogeneity, slab depth and slope angle on snowpack stability. Finally,
the importance of smoothing effects is verified and the crucial impact of heterogenity
characteristics on the so-called knock-down effect on slope stability is revisited using this
model.
16:30 - 16:45
1245
Relating weak layer and slab properties to snow slope stability
Jürg Schweizer1, Benjamin Reuter1, Sascha Bellaire1
NIENTE DI
CHE !
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
1
Snow slope stability evaluation requires considering weak layer as well as slab properties
- and in particular their interaction. The thickness and properties of the slab layers will
strongly influence failure initiation, but also crack propagation crucially depends on slab
properties. Of course, initiation and propagation is only possible with a weak layer prone
to fail that offers a suitable crack path. We derive snow properties from gridded snowmicropenetrometer measurements from 13 snow slopes. Micro-structural as well as bulk
properties of weak and slab layers were related to slope stability assessed with
compression tests and other observations of instability. Instead of applying a fully
mechanical approach that requires profile-specific finite element modeling, we aimed at a
classification scheme so that SMP resistance profiles can be classified in terms of
stability into poor, fair and good.
16:45 - 17:00
853
Application of a simple snow cover model to avalanche warning systems
Kouichi Nishimura1, Asami Komatsu2, Kazuhiro Tanji2, Naoki Matsuoka2
N. 1 foto
Nagoya University, Nagoya, Japan, 2Japan Weather Association, Sapporo, Japan
1
Esempio di
Soglie di allerta
Per Valerio/CLV
Today, road administrators monitor surface avalanche risk by measuring snowfall.
However, such a method will not enable them to forecast an avalanche occurrence
because there may be various causal factors for an avalanche.
Our study proposes one simple snow cover model that can be applied to snow
transformation. The model can estimate snow temperatures and density from
meteorological data including air temperatures and snowfall (or rainfall). A stability index
SI can be obtained by applying the shear formulation and slope inclinations to the model.
We have created an avalanche warning system that issues SI forecast from Numerical
Weather Prediction System (NWS) which is updated every hour. The performance of this
model has been verified by using the data of past avalanches.
In a significantly windy area, the model could not accurately estimate snow cover profile
only with the snowfall because in a windy area, snow is moved by winds as blowing
snow. To obtain more accurate snow cover profile in windy areas, we have developed an
algorithm that can be used to calculate snow transport by saltation and suspension so
that enables the calculation of snow accumulation and erosion that frequently occur on
the surface at wind convergence zones. This algorithm consists of k-epsilon model and
the snow budget balance proposed by Takeuchi (1975).
To verify this algorithm, we observed wind and snow transport state along the road in
Wakkanai, Hokkaido where an avalanche was occurred on the roadside by a heavy
snowstorm. The observation was conducted from a moving vehicle equipped with
meteorological instruments.
Molto localizzato!
17:00 - 17:15
955
Modelling the snow-atmosphere energy balance and its implication for wet-snow
avalanche formation processes
Christoph Mitterer1, Benjamin Reuter1, Alec van Herwijnen1, Charles Fierz1, Jürg
Schweizer1
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
1
The snow-atmosphere energy balance provides the input for various snow cover
processes, such as ablation (melt), sublimation or snow metamorphism. The energy
fluxes at the snow surface are key factors contributing to avalanche formation. Measuring
the spatial variability of these fluxes in complex terrain is virtually impossible. The most
reasonable approach is therefore to use a snow cover model and verify it by
measurements at selected locations. We investigate the snow-atmosphere energy fluxes
and its influence on snow avalanche formation processes for the Steintälli basin above
Davos, in the Eastern Swiss Alps. We used the 1-D snow cover model SNOWPACK to
compute the energy balance and its components based on data from three automatic
weather stations. One of the stations is located on a flat field within the basin, while the
other two stations are situated on a ridge and on an inclined southwest-facing slope,
respectively. In a first step, we verified the reliability of the simulations by comparing the
energy balance at the southwest-facing slope once computed with data from the slope
and once with extrapolated data from the flat field. In a second step, we investigate the
role of energy input and melt water production within the basin with respect to avalanche
formation during two wide spread wet-snow avalanche cycles in the spring of 2010.
Continuous seismic data from a geophone inserted in the snow cover in an avalanche
start zone were used to obtain avalanche activity data for the basin. We will present
results showing the relative importance of either radiation or turbulent fluxes on the
process of wet-snow avalanche formation.
17:15 - 17:30
418
n. 1 foto
Monitoring the temporal evolution of snow cover properties with upward-looking radar
systems
Lino Schmid1,2, Achim Heilig3,4,5, Christoph Mitterer1, Jürg Schweizer1, Robert Okorn6,
Hansruedi Maurer2, Olaf Eisen4,5
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland,
Institute of Geophysics, ETH Zurich, Zürich, Switzerland, 3Department of Geosciences
CGISS, Boise State University, Boise, United States, 4Institute of Environmental Physics,
University of Heidelberg, Heidelberg, Germany, 5Alfred Wegener Institute for Polar and
Marine Research, Bremehaven, Germany, 6Electronic & Technology Management
(ETM), FH JOANNEUM Gesellschaft mbH, Kapfenberg, Austria
1
2
Snow stratigraphy is a key contributing factor for assessing avalanche danger. So far,
only destructive methods can provide this kind of information. However, destructive
methods prevent a continuous monitoring of the temporal evolution of the snowpack.
Furthermore, parameters relevant for avalanche formation, such as the amount of new
snow, the settlement or percolating water, cannot be measured automatically. Radar
technology provides information on the snowpack non-destructively and allows deriving
internal snow properties from its signal response. During three consecutive winter
seasons from 2010-2011 to 2012-2013, we recorded continuous data from upwardlooking impulse radar systems (upGPR) at two different locations. The amount of new
snow during a snowfall event was calculated from the radar signal by subtracting the
height of the reflection of the old snow surface from the height of the new snow surface.
Manual measurements of the new snow amount were generally in good agreement with
the values calculated with our radar algorithm. Furthermore, we were able to track the
reflection of the old snow surface for up to 4 months after its initial burial. To verify the
settling signature within the radar signal, we deployed light-weight sensors attached to
potentiometers on the snow surface before every significant snow fall. These sensors
settled with the old snow surface. Settlement curves derived from the radar and
measured directly were in very good agreement. To assess the wetness of the
snowpack, we formulated an algorithm based on the magnitude of reflection amplitudes.
High reflection amplitudes correspond to large differences in permittivity - in our case the
transition from dry to wet. Compared to wet-snow avalanche activity and lysimeter data,
the automated pick of the dry-to-wet transition was encouraging, suggesting that such
data may be used to forecast wet-snow avalanches in notoriously difficult to assess
avalanche paths.
17:30 - 17:45
No abstract
Laboratory growth and bi-directional visible reflectance of surface hoar
10. Jul. 2013
Schwarzhorn
Session
08:15 - 09:45
D1a
Economics of weather and climate risks
08:15 - 08:45
422
Assessment of risk and opportunities related to climate change as contribution to the Swiss
Adaptation Strategy
n. 10 foto
Michael Bründl1, Niels Holthausen2, Peter Locher2, Lilian Blaser2, Sabine Perch-Nielsen2, Marco
Pütz3, Pamela Köllner-Heck4, Martina Zoller4, Thomas Probst4, Roland Hohmann4
x JP
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, 2Ernst Basler
+ Partner, Zollikon, Switzerland, 3Swiss Federal Institute for Forest, Snow and Landscape
Research WSL, Birmensdorf, Switzerland, 4Federal Office for the Environment, Bern,
Switzerland
1
In many countries adaptation strategies are being developed in order to cope with the
expected consequences related to climate change but also to judge the opportunities. As a
contribution to the Swiss adaptation strategy, a semi-quantitative assessment of risk and
opportunities in several sectors like e.g. health, agriculture or energy, is conducted on a
regional scale. The results from regional case studies conducted in six cantons are used for
upscaling to the whole of Switzerland.
We quantify the effects of climate change to short-term hazards like e. g. heat waves but also
to long-term and slow on-set changes, as e.g. the rise of mean air temperature. Where
quantification is not possible, we rely on qualitative information. For each sector we evaluate
the annual risks and opportunities for the situation today (2010) and for 2060 by considering
two climate change scenarios and one socio-economic and demographic scenario. The results
are compared across all sectors depicting the uncertainties and clearly stating all assumptions.
Here, we present the results of the case study “Canton of Aargau”, representing the region
“Mittelland” in Switzerland. Our investigations suggest a relatively large climate-induced
increase in human health risk, and a relatively large increase in opportunities in the energy
sector (reduction of heating). The increase in human health-related risk is mainly due to an
increased mortality of elderly people caused by more frequent and more intense heatwaves,
as well as to an increased exposure to allergenic pollen caused by a longer vegetation period.
The results from all regions will allow for comparing the different sectors and will provide a
sound basis for authorities and stakeholders to decide where to put on priorities in adaptation
measures related to Climate Change in Switzerland.
08:45 - 09:15
306
Economics of climate adaptation - a call to manage total climate risk
David Bresch1
n. 7 foto
1
Risk Management, Swiss Re, Zurich, Switzerland
x JP
Climate Adaptation measures are available to make cities more resilient to the impacts of
climate change. But decision-makers need the facts to identify the most cost effective
investments. Climate adaptation is an urgent priority for the custodians of national and local
economies, such as finance ministers and mayors. Such decision-makers ask: What is the
potential climate-related loss to our economies and societies over the coming decades? How
much of that loss can we avert, with what measures? What investment will be required to fund
those measures - and will the benefits of that investment outweigh the costs? Our Economics
of Climate Adaptation (ECA) methodology provides decision-makers with a fact base to
answer these questions in a systematic way. It enables them to understand the impact of
climate change on their economies - and identify actions to minimize that impact at the lowest
cost to society. It therefore allows decision-makers to integrate adaptation with economic
development and sustainable growth. See
http://media.swissre.com/documents/rethinking_shaping_climate_resilent_development_en.pdf
Seehorn
Session
08:15 - 09:45
C5.2a
Changing snow and ice hydrology in mountain watersheds
08:37 - 08:59
1276
Radiative forcing by light absorbing impurities in snow: partitioning impacts from mineral dust
and black carbon
Sara McKenzie Skiles1,2, Thomas H. Painter1,2
Joint Institute for Regional Earth System Science and Engineering (JIFRESSE), UCLA, Los
Angeles, CA, United States, 2Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA, United States
1
Melt of annual mountain snow cover dominates water resources in the western United States.
Recent studies in the Upper Colorado River Basin have shown that radiative forcing by light
absorbing impurities (LAIs) in mountain snow cover has accelerated snowmelt, impacted runoff
timing and magnitude, and reduced annual flow. However, those studies have assumed that
these LAIs are primarily mineral dust and have not considered the contribution of
carbonaceous particles from industrial and urban sources. Here we quantify both dust and
black carbon content and assess their relative contributions to radiative forcing in snow using a
suite of advanced field, lab, and modeling techniques.
Daily measurements of surface spectral albedo and optical grain radius were collected with a
field spectrometer over the 2013 spring melt season in the San Juan Mountains, CO,
Southwestern US. Coincident snow samples were collected and processed for; (1) dust and
black carbon content (2) impurity particle size, and (3) impurity optical properties. Measured
snow/impurity properties were then used to drive the Snow, Ice, and Aerosol Radiation
(SNICAR) model. Unique model runs for clean snow, only dust, and only black carbon allow us
to partition the radiative contribution from each constituent. This combination of
measurements, collected for the first time coincidentally and at such high temporal resolution,
and modeling allows us to better resolve the physical relationship between impurities, snow
properties, and surface albedo. Understanding these processes at the point scale facilitates
the upscaling of this understanding to constraining LAI radiative forcing retrievals by remote
sensing, and to regional climate and hydrology models- where currently the representation of
light absorbing of impurities is poor, and amplification of biases limits the ability to accurately
represent snow cover.
09:29 - 09:44
993
Methodology for snow cover reconstruction using in-situ observations and remote sensing data
Abror Gafurov1, Sergiy Vorogushyn1, Alexander Merkushkin2, Doris Düthmann1, Bruno Merz1
1
2
Section 5.4: Hydrology, GFZ German Research Centre for Geosciences, Potsdam, Germany,
Uzbek Hydrometeorological Service (Uzhydromet), Tashkent, Uzbekistan
Spatially distributed snow cover information can be well observed from remote sensing with
acceptable accuracy in remote areas such as Central Asian Mountains. However, these data
are available only for recent years or decades after satellite missions with proper snow
detection capabilities were launched. Yet, longer time series of snow cover data are required,
particularly in order to calibrate hydrological models in Central Asia where richer
meteorological and hydrological data are available in the past compared to the present state.
In this study, we present a methodology to reconstruct historical snow coverage using recent
available remote sensing data and point information on snow cover observed in the past at
existing meteorological stations. It consists of five subsequent steps which estimate historical
snow cover using among others the relationships between point observations and spatial snow
patterns considering seasonal snow cover characteristics and elevation controls. The
methodology is tested in Zerafshan basin of Central Asia. Obtained results are cross-validated
against high resolution remote sensing data and accuracy of about 90 % was achieved. The
methodology can be used to compensate the data gap on spatial snow cover for past decades.
Seehorn
Session
10:15 - 11:45
C5.2b
Changing snow and ice hydrology in mountain watersheds
10:15 - 10:37
1264
Comparing a distributed temperature-index and energybased model in mountainous watershed
Mukesh Kumar1, Danny Marks2, Jeff Dozier3, Michele Reba4, Adam Winstral2
Nicholas School of Environment, NC, United States, 2USDA Agricultural Research Service,
Boise, United States, 3Bren School of Environmental Science & Management, University of
California, Santa Barbara, Santa Barbara, United States, 4Watershed Physical Processes
Research Unit, USDA Agricultural Research Service, Oxford, United States
1
Two commonly used strategies in modeling snowmelt are the energy balance and
temperature-index methods. Here we evaluate the distributed hydrologic impacts of these two
different snowmelt modeling strategies, each in conjunction with a physics-based hydrologic
model (PIHM). Results illustrate that both the Isnobal energy-balance and calibrated
temperature-index methods adequately reproduce snow depletion at the observation site.
However, the models exhibit marked differences in the distribution of snowmelt. When
combined with PIHM, both models capture streamflow reasonably during calibration year
(WY06), but Isnobal model gives better streamflow results in the validation year (WY07). The
uncalibrated temperature-index model predicts streamflow poorly in both years. Differences
between distributed snow melt as predicted by Isnobal and calibrated temperature-index
method, and its consequent affect on streamflow prediction suggests the need to carefully
calibrate temperature-index models in both time and space.
10:37 - 10:59
686
The effect of canopy gaps on incoming radiation at the snow surface and implications for
snowpack retention in forested regions
Timothy Link1, Chad Ellis2, John W. Pomeroy2, Robert R. Lawler3, Richard Essery4, Danny
Marks5
n. 8 foto
College of Natural Resources, University of Idaho, Moscow, United States, 2Geography &
Planning, University of Saskatchewan, Saskatoon, Canada, 3U. S. Forest Service, Colville,
United States, 4School of GeoSciences, University of Edinburgh, Edinburgh, United Kingdom,
5
Northwest Watershed Research Center, USDA Agricultural Research Service, Boise, United
States
1
In mountainous, forested environments, vegetation exerts a strong control on snowcover
dynamics that in turn affect ecohydrological processes, streamflow regimes, and riparian
health. Snowcover deposition and ablation patterns in forests are controlled by a complex
combination of canopy interception processes coupled with radiative and turbulent heat flux
patterns related to topographic and canopy cover variations. In most seasonal snow
environments, snowcover ablation dynamics in forests are dominated by net radiation. Recent
research indicates that in small canopy gaps, an all-wave incoming radiation minima relative to
both open and forested environments can occur, but depends strongly on solar angle, gap
size, slope, canopy height and stem density. The optimal gap size to minimize radiation to
snow was estimated to have a diameter between 1 and 2 times the surrounding vegetation
height. Physically-based simulations of snowpack dynamics at a high-latitude site indicate that
gaps may increase SWE and desynchronize snowmelt by approximately 3 weeks between
north and south facing slopes, relative to undisturbed forests. On east and west facing slopes,
small gaps cause melt to be slightly delayed relative to intact forests, and have a minimal
effect on melt synchronicity between slopes. These results indicate that forest gap thinning
may be used to reduce snowmelt rates and/or alter melt synchronicity, but the exact
configuration will be highly spatially variable. Development of management strategies to
conserve water on the landscape to enhance forest and riparian health in a changing climate,
must also rigorously evaluate the effects of specific hydrometeorological conditions on net
radiation, turbulent fluxes, and snow interception processes.
10:59 - 11:14
997
Rain on snow: the impact of climate warming on the spatial variability of snow and mountain
hydrology
Danny Marks1, Adam Winstral1, Tim Link2, Michele Reba3, Mukesh Kumar4
n. 1 foto
USDA-ARS-NWRC, Boise, United States, 2Forest Science, University of Idaho, Moscow,
United States, 3National Sedimentation Laboratory, USDA-ARS, Jonesboro, United States,
4
Nicholas School of Environment, Duke University, Durham, United States
1
The hydrology of mountain regions is determined by precipitation phase, volume and
distribution. The complexities of precipitation volume and distribution are the result of a
complex interplay between regional orographic effects, and local-scale wind field interaction
with vegetation and topographic structure. Air-mass characteristics interact with the elevation
range of mountain systems to determine the precipitation phase and the elevation of the rainsnow transition. The makeup of forest and river systems in mountain basins is a reflection of
the stability of the rain-snow transition elevation over a long period of time. However, in a
rapidly changing and warming climate, the rain-snow transition is no longer stable, and is
moving to higher elevations. This continues to have a dramatic impact on mountain hydrology,
streamflow, and our ability to predict water supplies from mountain regions. As an example of
how dynamic these changes can be we present a combination of measurements and
simulation of conditions during a major rain-on-snow event that occurred between Dec 25,
2005 and Jan 1, 2006, over an 800m elevation range in a 14 km 2 mountain catchment. During
the event, 174 mm of precipitation fell on the basin, representing approximately 20% of the
water year total precipitation, with multiple transitions between rain and snow along the
elevation gradient. This event illustrates the potential impact a warmer climate may have on
mountain hydrology and streamflow in western North America.
11:14 - 11:29
378
Snow cover variation over Turkiye
Ahmet Tekeli1, Ibrahim Sonmez2, Erdem Erdi3
Civil Engineering, King Saud University, Riyadh, Saudi Arabia, 2Department of Meteorology,
Ondokuz Mayıs University, Samsun, Turkey, 3Remote Sensing Division, Turkish State
Meteorological Service, Ankara, Turkey
1
Rivers originating from the mountainous regions in Tϋrkiye mainly get their water from the
melting of snow accumulated during the winter time on these mountains. Thus monitoring
snow cover and its variation is important for accurate water resources management. Despite
the importance of snow cover there is no operational snow cover monitoring over Tϋrkiye, yet
and limited information is available by the in-situ observations about the snow cover variation.
In this study, daily snow cover data from interactive multisensor snow and ice mapping system
(IMS) by NOAA/NESDIS is used to examine the snow cover trend over Turkey. The daily IMS
data and in-situ snow depth measurements from 219 synoptic and climate stations covering
2004-2011 period are used as ground truth data.
Initially, validation of IMS product is performed and contingency tables including the categorical
statistics of probability of detection (POD) and false alarm rate (FAR) are derived in daily and
seasonal basis. The POD value of 0.723 and FAR value of 0.208 is obtained for the whole
study area of Tϋrkiye. The same statics are derived for the seven geographical sub-regions of
Tϋrkiye to introduce the spatial variation of the product accuracy. The highest POD amount,
0.801, is obtained for the Eastern Anatolia Region and the lowest, 0.451, is seen in SouthEastern Anatolia Region.
Non-parametric test of Mann-Kendall is performed to examine trend presence for the snow
cover. The test results with significance level of 0.05 indicated that both the whole domain
(Tϋrkiye) and all the sub-regions indicated negative trend. Significantly positive trend is
obtained for Tϋrkiye and all sub-regions for the autumn season. On the other hand, negative
trend is obtained for the same regions in spring and summer seasons. For the winter season,
only the Aegean Region, indicated positive while all the others indicated negative trend.
11:29 - 11:44
1048
Soil temperature and water dynamics on contrasting aspects in the rain-snow transition zone
Mark Seyfried1, Tim Link2, Sage Bryden2
n. 3 foto
USDA-ARS-NWRC, Boise, United States, 2Forest Science, University of Idaho, Moscow,
United States
1
x Michèle
Understanding how complex terrain affects hydrological and biogeochemical processes has
become increasingly important as the global climate changes. Soils modulate both fluxes and
are therefore central to this understanding. We are particularly interested in soil temperature
and water content because they exert strong controls on hydrologic and biogeochemical
fluxes. We measured soil water (θ) and temperature (Ts) profiles at three paired locations in
mountainous, complex terrain in SW Idaho, USA (~43°latitude). Each pair consisted of a soil
profile of temperature and water content from a depth of 5 cm to bedrock (50 to 110 cm) on
opposing north and south facing slopes at the same elevation. The sites are located near the
rain/snow transition elevation for the area (1600 m) on steep slopes (25 to 40°) with sparse
vegetative cover. We measured dramatic differences between the two slopes, with a difference
of 9°C (at 50 cm) in August. Differences between slopes were smaller in winter, about 4° C.
The Ts difference between two opposing slopes at identical elevations that we measured is
practically the same as the difference between Ts measured on nearly level ground but
separated by 1000 m in elevation. This implies that we need to consider two snowmelt
seasons within a given watershed based on aspect. We expected θ on north facing soils to
decline more slowly and later in the year the south facing soils due to the evaporative demand
differential. We did not observe this and, in fact, θ on the two slopes responded similarly during
spring and early summer. This is attributed to two factors. First, spring rains were sufficient to
maintain relatively high soil water storage on both slopes. Second, the denser vegetative cover
on the north-facing slopes counters the lesser evaporative demand.
Seehorn
Session
13:15 - 14:45
C5.2c
Changing snow and ice hydrology in mountain watersheds
13:45 - 14:00
1139
Characterizing the spatial snow depth distribution in mountainous terrain
n. 6 foto
Nora Helbig1, Henning Löwe1, Thomas Grünewald1, Jan Magnusson1, Michael Lehning1, Tobias
Jonas1
1
SLF, Davos, Switzerland
Spatial snow depth information is an essential component for many applications, such as the
computation of snow melt rates in hydrologic applications or the energy balance in
meteorological or climate models. Due to computational constraints, small-scale distributed
modeling is rarely feasible for large regions. This is especially true over mountainous, complex
terrain. Sub grid parameterizations for spatial snow depth distributions are therefore
particularly valuable in the context of large-scale applications.
Past research has shown that for rather homogeneous landscape units the pre-melt spatial
distribution of snow depth can be approximated by a log-normal distribution. However, this is
no longer valid for wind-shaped snow distributions over landscape units covering complex
terrain. Seasonally recurring snow accumulation patterns have been reported, mostly shaped
by terrain and wind. We focus on large heterogeneous landscape units in order to investigate
the impact of topographic parameters on sub grid snow depth distribution at peak of winter with
sub grid cells on the order of 25 m. We analyze a new data set with a particular view on
developing a sub grid parameterization of snow depth for operational hydrologic applications
and verifying previously developed models. Snow depth data obtained from an airborne laser
scanning campaign in the Wannengrat Alpine catchment as well as from a unique optoelectronic scanning data set (Sensor ADS 80, Leica Geosystems) in the larger Dischma
catchment (40km2) are used. Both areas are located above Davos, in the eastern Swiss Alps.
A sub grid parameterization of snow depths variability at peak of winter will allow to compute
snow covered area as a function of spatial melt rates during the ablation period, an issue
which is also relevant for the parameterization of sub grid albedos in other large-scale models.
14:00 - 14:15
938
X info!
Estimating snow water equivalent from snow depth data: a comparison of different approaches
Gianluca Filippa1, Edoardo Cremonese1, Fabrizio Diotri1, Paolo Pogliotti1, Marta Galvagno1,
Umberto Morra Di Cella1
1
ARPA Valle d'Aosta, Saint Christophe, Italy
The snow water equivalent of a seasonal snowpack (SWE) is a piece of information of
paramount importance in alpine hydrology, since in alpine catchments the snowmelt often
constitutes the most significant portion of the total runoff. Estimating SWE requires
measurement of snow depth (hs) and snow density (rho), the latter being the most timeconsuming measurement. Here we present three approaches for modeling SWE at point level
from about 4000 SWE-hs-rho measurements conducted from 2006 to 2012 in Aosta Valley
(NW Alps). In the first approach SWE was obtained multiplying hs by the average of available
density measurements. In this approach we used (a) realtime rho (i.e. median rho of the
current month and year of measurement), and (b) historical rho (i.e. median rho of the current
month of all other years except current). The second approach consisted in modeling SWE
using mixed effect models, with hs, elevation and climatic sub-regions as explanatory
variables. This model was tested for either realtime data and historical data as in approach (1).
In the third approach SWE was modelled according to previously published equations
parametrized for the Swiss Alps (Jonas et al. 2009, J. of Hydrology) and for an enlarged
northern hemisphere dataset (Sturm et al. 2010, J. of Hydrometereology). Results show that (i)
approaches (1) and (2) do not substantially differ in terms of cross-validation modeling
efficiency; (ii) the use of historical data only slightly worsens SWE modeling, and including the
elevation as explanatory variable slightly improves estimates in both approaches (1) and (2),
suggesting that the amount of historical rho data would be sufficient to accurately predicting
future SWE from hs only; (iii) the use of previously published equations (approach 3) resulted
in much lower accuracy, suggesting that so far a general parametrization is not yet possible.
14:15 - 14:30
472
Using LiDAR data for enhanced simulation of snow accumulation distribution in hydrological
modelling of Alpine glacierized catchments
Florian Hanzer1, Kay Helfricht1,2, Katrin Schneider1, Thomas Marke3, Michael Kuhn2, Ulrich
Strasser1,3
alpS Centre for Climate Change Adaptation Technologies, Innsbruck, Austria, 2Institute of
Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria, 3Institute of
Geography, University of Innsbruck, Innsbruck, Austria
1
The project MUSICALS (MUltiscale Snow/Icemelt discharge simulations into ALpine
reservoirS) aims to predict meltwater contributions from snow and ice resources to discharge
into the Alpine reservoir of the Gepatsch system (Kaunertal, Ötztal Alps, Austria) using the
physically based snow model AMUNDSEN. The accurate simulation of melt discharge requires
a realistic reproduction of snow cover distributions by accounting for all processes and
parameters that govern snow accumulation and ablation in Alpine regions (e.g. large-scale
precipitation patterns, preferential deposition of snow, gravitational snow transport and the
local energy balance). While some of these processes are already accounted for in the applied
snow model, the regionalization of precipitation, which is currently based on corrections for
elevation only, does not yet allow to accurately reproduce the complex patterns in snow
deposition found in the considered catchment. To enhance model performance, a set of five
end-of-season snow accumulation patterns from LiDAR data for a glacierized subcatchment
(36 km²) located in the upper Rofental valley (Ötztal Alps) is utilized. Based on this data set, a
factor analysis has been carried out to identify the influence of different topographic
parameters on local snow distribution. The identified correlations were tested against one endof-season LiDAR data set covering an area of approx. 580 km² in the Ötztal Alps. By
incorporating the knowledge gained from this factor analysis into the snow model,
improvements in the simulation of both the glacier mass balance as well as the related
meltwater discharge could be achieved. Results are presented by showing the simulated
glacier mass balance and meltwater discharge in comparison to mass balance and discharge
observations in the highly glacierized Rofental valley. AMUNDSEN modelling results of
catchments adjacent to the Rofental are promising for an enhanced description of snow
redistribution, enabling reduced computational effort than would be required for explicit
process modelling.
14:30 - 14:45
643
upGPR as a tool for continuous, non-destructive, non-weighing snow-water equivalent
monitoring
Achim Heilig1,2, Lino Schmid3, Christoph Mitterer3, Juerg Schweizer3, Robert Okorn4, Olaf Eisen5
Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany,
Geosciences, Center for Geophysical Investigation of the Shallow Subsurface, Boise State
University, Boise, United States, 3SLF, Swiss Federal Institute for Forest, Snow and
Landscape Research WSL, Davos, Switzerland, 4Advanced Electronic Engineering, FH
JOANNEUM Gesellschaft mbH, Kapfenberg, Austria, 5Alfred-Wegener-Institute for Polar and
Marine Research, Bremerhaven, Germany
1
2
Upward-looking ground-penetrating radar (upGPR) in combination with conventional snow
depth sensors (e.g. ultra sonic range gauge) can be utilized to monitor continuously the snowwater equivalent (SWE) of a snowpack. Hereby, we combine measured snow depth of the
conventional device with recorded two-way travel time of the radar system to calculate
snowpack density and liquid water content. Due to the fact that upGPR is not weighing the
mass of the snowpack above a sensor system, it is not biased through bridging effects and can
be applied even in slope areas. Slope applications are depending on the capabilities of the
snow-depth sensors and are only limited for areas, where the above-snow device is prone to
avalanche destruction or snow creep. upGPR systems are currently installed in slopes above
Davos, Switzerland and above Boise, Idaho, USA as well as on the flat test site Weissfluchjoch
(Davos). At Weissfluhjoch, the described instrumentation has been run successfully over three
consecutive winter seasons. In comparison to manually observed SWE, the root mean
squared error (RMSE) for the radar derived SWE was lower than values obtained with the
snow pillow. The radar retrieved SWE values underestimated manual peak SWE, but the error
was less than half the magnitude of snow pillow derived recordings for the respective dates.
This study evaluates the feasibility of upGPR to record SWE continuously in slopes up to 30
degrees.
Sanada I
Session
13:15 - 14:45
C4.3c
Atmospheric boundary layers in complex terrain and over ice, snow and vegetated
surfaces
13:30 - 13:45
683
Boundary layer processes over a patchy mountain snow cover and associated changes in the
energy balance
Rebecca Mott1, Megan Daniels2, Michael Lehning1,3
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, 2Laboratory
of Environmental Fluid Mechanics and Hydrology, Ecole Polytechnique Fédérale de Lausanne
EPFL, Lausanne, Switzerland, 3Laboratory of Cryospheric Sciences, Ecole Polytechnique
Fédérale de Lausanne EPFL, Lausanne, Switzerland
1
Heterogeneous land-covers induce the formation of secondary flows and small-scale boundary
layer processes. While turbulent fluxes over a continuous snow cover are mostly governed by
the spatial variability of wind velocity and solar radiation, local advection of sensible heat and
boundary layer decoupling become additionally important for the surface energy exchange
over patchy snow covers. Furthermore, evolving katabatic and anabatic winds strongly change
the mean flow patterns over snow free and snow covered areas causing positive and negative
buoyancy production.
In this study we use an atmospheric model (Advanced Regional Prediction System) to
investigate boundary layer processes over patchy snow covers in an alpine catchment. The
model is initialized with low to high snow cover ratios based on field measurements of snow
distribution. We particularly analyse the effect of heat advection, boundary layer decoupling
and changing patterns of secondary flows on the energy balance at the local and catchment
scale.
The numerical results show that the changing land-cover controls the length scale of internal
boundary layers, while secondary flows drive the strength of boundary layer decoupling and
heat advection. The relative importance of boundary layer processes depend on the snow
patch size distribution and the synoptic wind. Stronger synoptic winds and low snow cover
ratios increase the effect of heat advection and decrease the impact of boundary layer
decoupling on the catchment`s melt behaviour.
The typical lengths of stable internal boundary layers coincide with snow patch size
distribution, which is consistent with typical length scales of snow accumulation patterns. As
those length scales are in the order of tens of meters for the studied alpine catchment, very
small grid sizes (below 10 m) are required to adequately model boundary layer processes
which are shown to significantly alter the energy balance over patchy snow covers.
Wisshorn
Session
16:15 - 17:45
B2.1b
The dynamics of extreme events – improving forecasts in the current climate
16:45 - 17:00
1006
Relationships between high precipitation events (HPE) in the Mediteranean area and upperlevel dynamics in a semi-idealized atmosphere
Philippe Arbogast1, Karine Maynard1
1
Météo-France, Toulouse, France
Southern France is prone to devastating flash-floods during the fall season . The warming and
moistening of the boundary layer through sensible and latent heat fluxes from the warm sea is
known as an efficient mechanism for convective destabilization and further production of heavy
precipitation. However the triggering of convection usually requires preexisting upper-level PV
coherent structures. Senstivity studies using PV inversion where PV features are removed
from a control simulations may help to understand the relationship between upper-level
dynamics and convection. Here, we suggest to build up an idealized initial state without any
synoptic-scale feature. Then, PV surgery consists of adding PV anomalies to the idealized
initial state with a full control of their shape and amplitude. The first result suggests that it is
possible to trigger significant amount of precipitation with an upper-level coherent structure
with a low propagation speed. Ensemble sensitivity analysis is also applied to address the
sentivity of the precipitation to some aspects of the coherent structure using the french global
ensemble PEARP.
17:00 - 17:15
924
Moisture transport in Mediterranean cyclones leading to extreme precipitation and flooding
events
Jana Campa1, Ulrich Corsmeier1
1
Institute for Meteorology and Climate Research, KIT Karlsruhe, Karlsruhe, Germany
Extreme weather events such as severe cyclogenesis with heavy precipitation and flashflooding regularly affect the Mediterranean region. The orography surrounding the basin further
enhances the formation of heavy rain. The aim of HyMeX (HYdrological cycle in the
Mediterranean EXperiment) is a better understanding and quantification of the hydrological
cycle and related processes in the region, focusing on high-impact weather.
In October and November 2012, during the HyMeX SOP, a series of three Mediterranean
cyclones reached the Gulf of Genoa and the Adriatic area bringing large amounts of moisture
in this region. They caused extreme precipitation with peaks of up to 400 mm/24 h and severe
flooding events with considerable damage and casualties. This study focuses on transport of
moisture involved in heavy precipitation.
A Lagrangian trajectory analysis has shown considerable amounts of moist air arriving from
the Atlantic, associated with a cyclone entering the Mediterranean from the Atlantic and later a
large scale trough situated over western and central Europe. The most extreme precipitation
occurred after the interaction of the moist air with the Alps and the Apennines. A combination
of COSMO model simulations and trajectory analysis enables the distinction between
advective and convective moisture transport.
The Lagrangian analysis of these events will be further extended by the analysis of the data
collected during the HyMeX SOP, such as radiosonde data, humidity measurements by
aircraft, boundary layer balloons, microwave radiometer.
Seehorn
Session
16:15 - 17:45
C5.2d
Changing snow and ice hydrology in mountain watersheds
16:37 - 16:59
370
Distributed catchment meltwater from fine resolution snow modeling in the rain-snow transition
zone
Patrick Kormos1, James P. Mcnamara1, Danny Marks2, Hans Peter Marshall1
Geosciences, Boise State University, Boise, United States, 2Northwest Watershed Research
Center, Agricultural Research Service, Boise, United States
1
The timing and magnitude of snow meltwater inputs are quantified for an experimental
catchment in the rain-snow transition zone in the foothills north of Boise, Idaho, USA for the
2011 water year. The rain-snow transition zone is climatically sensitive to warming
temperatures as most precipitation falls while dew point temperatures are close to zero. The
phase of precipitation at the catchment ranges from 36% to 81% snow during the 15 years of
record. The iSNOBAL model was run at a 2.5 m2 resolution at an hourly timestep from October
10th to July 1st. Validation data include an array of 6 ultrasonic depth sensors and a series of 10
weekly snow surveys. High-resolution modeling enables us to account for aspect related snow
patches that persist into the spring while the majority of adjacent slopes are snow free.
Approximately 7 rain-on-snow events are included during the simulation. The January 16th
event produced the largest streamflow peak for the study basin record of 15 years. Amount
and distribution of a ripe snowpack is important immediately before and after rain-on-snow
events, while less important during high-intensity rainfall.
16:59 - 17:14
944
High uncertainty in 21st century runoff projections from glacierized catchments
Matthias Huss1, Michael Zemp2, Philip Joerg2, Nadine Salzmann1,2
1
University of Fribourg, Fribourg, Switzerland, 2University of Zurich, Zurich, Switzerland
Climate change is expected to significantly alter the hydrological regime of glacierized
drainage basins. Quantifying the impacts of changing climatic conditions on snow and ice melt
runoff is important for future water resource management. However, the spread in climate
scenarios and insufficiently understood processes in the impact modelling result in
considerable uncertainties in projected high-mountain discharge.
Here, we provide an integrative quantification of the uncertainties in modelled glacier runoff
over the 21st century for the example of Findelengletscher, a valley glacier in the Swiss Alps.
We present time series of glacier area change and runoff until 2100 based on 10 Regional
Climate Models, and various parameterizations of important processes influencing simulated
glacier response to climate change. Runoff from the highly glacierized catchment of
Findelengletscher is simulated using the glacio-hydrological model GERM. Differences in
projected runoff are analyzed relative to (1) the RCM input, (2) the downscaling procedure, (3)
the availability field data used for model calibration, (4) the initial ice volume, (5) uncertainties
in snow accumulation distribution, (6) the method for calculating glacier geometry change, (7)
the type of melt model applied, (8) the snow albedo parameterization, (9) changes in bare ice
albedo, and (10) the effect of supra-glacial debris.
We find that the uncertainties in modelled glacier area loss, changes in discharge volumes and
the hydrological regime are considerable. Simulated glacier area change by 2075 lies within a
range of -35% and -95% compared to today; modelled changes in August runoff range
between +25% and -50%. Nevertheless, a trend towards a shift in the hydrological regime is
revealed by all model realisations. The choice of the RCM input is particularly important.
Among other factors a better description of the initial ice volume and winter accumulation data
are critical for reducing the uncertainties in the impact modelling.
17:14 - 17:29
201
Contribution of glaciers to the watershed in the semi-arid Andes of Chile
Shelley MacDonell1, Christophe Kinnard1, Simon Gascoin2
Centro de Estudios Avanzados en Zonas Áridas, La Serena, Chile, 2Centre d’Études Spatiales
de la Biosphère (CESBIO), Toulouse, France
1
The semi-arid Andes of Chile (26-32ºS) are characterised by relatively low temperatures, low
average relative humidity and low levels of precipitation. In this region, snow and ice melt is
thought to be the primary contributor to streamflow, and generally acts to alleviate drought
problems in otherwise dry spring and summer seasons. Due to the aridity of the climate,
sublimation is a dominant ablation process, which causes penitentes, or ice pinnacles, to form
on glacier surfaces. In this presentation we aim to understand the production of melt on planar
and penitente-covered glacier surfaces using energy balance modelling and eddy covariance
measurements in the present climate, and under future conditions. From our analysis we found
that the turbulent heat fluxes were significantly different between sites and that the roughness
lengths on the penitente surface were longer than on the planar surface, which enabled more
sublimation to occur. Additionally the penitente trough had a lower albedo than the planar
surface which increased the modelled melt rate. The ratio of sublimation : melt was different
between sites, as sublimation dominated the planar surface ablation fraction, whereas melt
dominated the penitente signal. The main limitation to melt on the planar surface was surface
temperature, as the ice was generally below the melting point. By using projections to 2080
(which suggest a mean warming of 2-3.5ºC annually, and a decrease in mean annual
precipitation of 15-20%) we find that the ratio of ablation on planar surfaces is dramatically
changed, and the quantity of ablation on penitente surfaces is greatly increased. However,
whilst such changes will help to ease the arid conditions experienced lower in the watershed in
the short-term, it is unsustainable, and likely to lead to the decay of glaciated areas in the
region.
17:29 - 17:44
195
Long and short term changes in ecologically important proglacial groundwater-fed systems of
two retreating glaciers in SE Iceland
Amir Levy1, Zoe P. Robinson1, Stefan Krause2, Richard I. Waller1, John Weatherill1
Research Instuture for the Environment, Physical Sciences and Applied Mathematics
(EPSAM), Keele University, Keele, Staffs, United Kingdom, 2School of Geography, Earth and
Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
1
Groundwater-fed surface water systems in glaciated basins are ecologically important due to
their distinct physiochemical characteristics, which impact water temperature, nutrient
availability, turbidity and discharge. Yet, despite the importance of these systems, there has
been a paucity of research on the impact of changes in catchment glaciation on proglacial
groundwater systems and their interaction with surface water systems.
This presentation investigates changes in proglacial groundwater-fed systems at two retreating
glaciers (Skeiðarárjökull and Skaftafellsjökull) in SE Iceland over different temporal scales. It
draws on groundwater level data (collected between 2000 and 2012) at different spatial and
temporal resolutions, remotely-sensed mapping of groundwater seeps and physiochemical
parameters of groundwater and surface water systems.
These data show that proglacial groundwater levels have dropped considerably over the past
decade, although there are substantial variations in groundwater levels, at the annual,
seasonal and event time scales. Mapping of long-term changes in the spatial extent of
ecologically-important groundwater seeps and lakes (using aerial photographs from 1978,
1997 and 2007) shows a significant decrease in the extent and size of groundwater seeps and
lakes. Spatial analysis shows that the area of groundwater seeps has decreased by
approximately 90% between 1978 and 2007. Reductions of similar magnitude have also been
observed in the sizes of large groundwater-fed lakes at the field site. These changes in
groundwater level have clear impacts on the physiochemical properties of these groundwaterfed surface water bodies and their dependent ecosystems. These different scale changes to
the proglacial groundwater systems may be attributed to a wide range of different factors,
including changes in glacial extent, variations in precipitation, changes in the position of fluvial
meltwater channels, isostatic uplift and the interaction between these different factors.
11. Jul. 2013
Seehorn
Session
08:15 - 09:45
C5.1a
Past, current and future water, snow and ice availability, use, and management in
mountain regions
08:15 - 08:37
1018
The representation of current and future mountain snow cover by state-of-the-art regional
climate models
Sven Kotlarski1, Daniel Lüthi1, Christoph Schär1
n. 13 foto
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
1
Michéle
08:37 - 08:59
n. 1 foto
Recent decades have seen a continuous evolvement of global and regional climate
models (GCMs, RCMs) into earth system models, accounting for an increasing number
of processes that link the atmosphere to further components of the climate system. Part
of this evolution has been a refined description of land surface processes, including the
simulation of the surface snow pack. In a fully coupled climate model, surface snow cover
is interactively coupled to the atmospheric model component, providing physically
consistent snow responses to climate variability and climate change.
While continental-scale snow cover variability as represented by climate models has
been assessed in a number of previous studies, the analysis of snow cover
characteristics in mountainous terrain has for long been hampered by a comparatively
coarse climate model resolution. The most recent RCM scenarios now provide output at
resolutions down to a 10 km scale and thereby offer the possibility for snow cover
analysis and snow cover projections in topographically structured terrain.
This contribution presents an overview on possibilities and on limitations of RCM data
concerning the analysis of the mountain snow pack. A focus is put on the European Alps,
a region with a high societal and economical significance of snow conditions. The ability
of state-of-the-art RCMs to reproduce Alpine snow cover will be assessed and scenarios
for the 21st century will be presented. Both the well-established experiments provided by
the ENSEMBLES project at a resolution of 25km as well as recent high-resolution
scenarios carried out within the ongoing Euro-CORDEX initiative at resolutions down to
12km will be considered. Analyzed parameters include mean snow water equivalent, but
also the length of the snow season and the timing of snow onset and snow meltout at
different altitudes.
1064
10-years snow cover variability over Switzerland derived from satellite data-a contribution
to the National Climate Observing System (GCOS Switzerland)
Nando Foppa1, Gabriela Seiz1
Swiss GCOS Office, Federal Office of Meteorology and Climatology MeteoSwiss, Zurich,
Switzerland
1
The estimation of snow parameters such as snow extent, snow depth, and snow water
equivalent plays a vital role in the Swiss Alps for winter tourism as well as for the
management of water resources. Therefore, ground-based monitoring of the snow cover
has a long tradition in Switzerland and a number of studies have been published over the
last years, focusing on its temporal variability and long-term trend. Most of these studies
concentrated on the spatiotemporal variability of snow cover days (SCD).
The Implementation Plan of the Global Climate Observing System (GCOS) emphasises
the importance to strengthen and maintain snow cover observations, ideally
supplemented with other observing systems. At the national level, climate relevant
measurements, including snow and hydrological parameters, are coordinated by the
Swiss GCOS Office at MeteoSwiss. Compared to ground-based observations with the
limitation of being sparse, satellite data give an area-wide and spatially consistent
information and complement high-quality in-situ snow observations.
In our presentation, we focus on the inter-annual variations of SCD from October 2000 to
September 2010 based on data from the Moderate Resolution Imaging
Spectroradiometer (MODIS) on board the Terra platform. The purpose is to examine the
spatiotemporal variation of the snow conditions on a yearly basis over Switzerland by
implementing a cloud-gap filling technique. The multi-year time series of SCD on an
annual basis are compared with selected in-situ snow observations and further discussed
on a monthly and daily resolution to demonstrate the potential of our SCD product.
References:
Foppa, N. & Seiz, G. 2012. Inter-annual variations of snow days over Switzerland from
2000-2010 derived from MODIS satellite data. The Cryosphere, 6, 331-342,
doi:10.5194/tc-6-331-2012.
08:59 - 09:14
671
Trend analysis of snow water equivalent in the Alpine region
Christoph Marty1, Anna-Maria Tilg2, Tobias Jonas1
WSL – Institute for Snow and Avalanche Research SLF, Davos, Switzerland, 2University
of Innsbruck, Innsbruck, Austria
n. 11 foto
(particolarmente
interessante n.1)
1
The temporary storage of water in form of snow plays an important role in the water
cycle. It impacts the seasonal discharge and the water supply in many areas of the world.
The regional and annual variability of SWE is important for the maximum snow load
codes or the hydropower industry, which is interested in detailed forecasts of the
discharge for efficient energy production. In spring the snow water equivalent (SWE) is of
particular significance to forecast the magnitude of snowmelt runoff to issue possible
flood warnings.
In this study we analyze the long-term variability and trends of SWE measurements at
roughly 50 stations to determine how climate change impacts the snow water resources.
We show results of long-term measured SWE and snow density data from different
regions in the Alps between 1936 and 2012. The measurement sites are located between
500 and 2500 m asl in Austria, Germany, France and Switzerland. Almost two dozen of
these sites are operational since 60+ years. Mid-winter and spring snow pack trends
have been investigated separately. The results reveal that the majority of the stations
show non-significant negative trends in all regions. The strongest relative trends are
observed in spring at low altitude.
09:14 - 09:29
636
Future trends of the Alpine and ephemeral snowpack at selected sites across
Switzerland
Edgar Schmucki1,2, Christoph Marty1, Charles Fierz1, Michael Lehning1,3, Rolf Weingartner2
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland,
Institute of Geography and Oeschger Centre for Climate Change Research, University of
Bern, Bern, Switzerland, 3CRYOS, School of Architecture, Civil and Environmental
Engineering, EPFL, Lausanne, Switzerland
1
2
Snow is a key feature of mountainous environments because of its high implications for
hydrology, vegetation and economics, such as winter tourism or hydropower. In
particular, snow depth, the stored snow water equivalent, the snow load on a roof or the
duration of the snow on the ground are all important parameters for services like road
maintenance, avalanche warning, water management, hydro power, flood prevention or
building code regulations. The measurement of these snow parameters is either not
always possible or too expensive. To overcome this problem, simple snow models with
input from meterological stations are sometimes used.
In this study we apply the complex one-dimensional, physically based snow model
SNOWPACK. We first demonstrate the performance of SNOWPACK in modeling the
seasonal evolution of snow characteristics such as snow depth or duration of snow cover
for single years. The input data SNOWPACK requires includes air temperature, relative
humidity, wind speed and direction, incoming short- and long-wave radiation, and
precipitation intensity. As most stations do not measure incoming long-wave radiation, it
needs to be parameterized. Moreover, due to wind-induced errors, it is not meaningful to
use precipitation measurements directly as an input into SNOWPACK, so they need to
be calibrated or corrected.
In a second step we show future trends of the Swiss snowpack at selected sites located
at different elevations across Switzerland. Therefore we concentrate on the ability of
SNOWPACK to model climatological mean values of seasonal snow depth, maximum
snow depth and the length of snow season for example. For the assessment of future
trends, scenario data from the recently released CH2011 report will be used in order to
perturb the observed time series of temperature and precipitation.
09:29 - 09:44
146
Impact of the CH2014 climate scenarios on water resources - an estimate for Switzerland
Luzi Bernhard1, Christoph Pflugshaupt1, Sven Kotlarski2, Stefanie Jörg-Hess1, Tobias
Jonas3, Massimiliano Zappa1
Hydrological Forecasts, Swiss Federal Institute for Forest, Snow and Landscape
Research WSL, Birmensdorf, Switzerland, 2Institute for Atmospheric and Climate
Science, Swiss Federal Institute of Technology, Zürich, Switzerland, 3Snow Hydrology,
Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf,
Switzerland
1
The projected climate change might have significant impacts on snow cover and glaciers,
and thus on Alpine water resources. Within the study CCHydro (BAFU) we realized high
temporal and spatial resolution scenarios of the water cycle and the discharges for the
different climates and elevations of Switzerland. To reflect the estimated local climate
change in a large basin, the climate scenarios of the ENSEMBLES project were
calculated, using the delta change method on a daily basis, based on the A1B emission
scenario for temperature and precipitation.For the periods 2021-2050 and 2070-2099
were simulated the local meteorological changes and the resulting changes in the
glaciation, the snowpack and runoff in comparison with the control period 1980-2009.
These studies have been extended by the use of the CH2014 scenarios by MeteoSwiss.
These are based on a probabilistic method, representing the model uncertainty and the
decadal variability. In contrast to the delta change approach, the projected climate data
are available for five regions of Switzerland only. In addition to the A1B scenario two
further emission scenarios are provided: RCP3PD (moderate) and A2 (“worst case”).
Looking at the expected changes, primarily the ice melt part of the total runoff will decline
(-22%) in the first half of this century, which is expected to level off by the end of this
century. However, the snow melt fraction of the total runoff is expected in the near future
by about 15% and decrease in the second period by up to 40%. If we compare the A1Bbased CCHydro results with the optimistic scenario RCP3PD, we can clearly
demonstrate that a reduction of greenhouse gases will have a positive effect by the end
of the century. In contrast, the A2 results are comparable with the A1B values, with
stronger anomalies by the end of the century.
Aspen II
Session
10:15 - 11:45
A5.5a
Open alpine cryosphere session
10:15 - 10:45
550
Impacts and risks of cryosphere change: what has been observed and what is projected?
Christian Huggel1
n. 6 foto
Department of Geography, University of Zurich, Zürich, Switzerland
1
Michèle
The alpine cryosphere is subject to strong changes, with glaciers rapidly shrinking,
permafrost thawing, and snow cover decreasing. Improved monitoring techniques, in
particular related to remote sensing, has allowed to increasingly document changes of
the cryosphere in many high mountains of the world. The impacts, implications and risks
of cryosphere changes, however, are often less visible and less well documented,
although there exists little doubt that water resources, hydropower, tourism, agriculture or
damage due to natural hazards have been or will be affected.
In this contribution we focus on the following questions:
(1) Where and to what extent have we observed impacts related to cryosphere changes?
(2) What are the economic and social implications and risks of these changes?
(3) How will future cryosphere changes impact high mountains and downstream
systems?
To address these questions we draw on examples and case studies from the Alps,
Andes and Himalaya.
10:45 - 11:00
87
Snow hazards in Lesotho: implications for human and livestock vulnerability in a
developing mountain region
Stefan Grab1, Jonathan Linde1
School of Geography, Archaeology & Environmental Studies, University of the
Witwatersrand, Johannesburg, South Africa
1
Alpine cryospheric hazards are becoming increasingly prominent under current global/
regional climate change scenarios and receiving wide scientific coverage from, in
particular, northern hemisphere mountain regions associated with glaciers, permafrost
and extensive seasonal snow cover. However, there is a general paucity of knowledge
and attention on cryospheric hazards associated with mountain environments only
occasionally/rarely impacted by heavy seasonal snowfalls or severe frost events,
particularly those in developing and southern hemisphere regions.
Heavy and prolonged snow cover in the Lesotho Highlands sometimes carries the
consequence of human and livestock deaths owing to isolation, exposure and underpreparedness in this developing region of southern Africa. Firstly, this paper aims to
quantify the changing temporal dynamics of snow hazards and associated consequences
in Lesotho from 1830-2012, based on archived documentary evidence and more recent
satellite imagery. Secondly, we use daily MODIS snow cover images for the period 20032010, in combination with high-resolution SPOT satellite images, to establish the recent
finer-scale frequency, extent and timing of snowfalls across Lesotho. A digital shapefile
containing the location, name and district attributes of 2016 villages across Lesotho is
used to determine village vulnerability to the negative impacts associated with prolonged
snow cover. A ranking system is applied to each village according to the seasonal
duration of snow cover, and the accessibility and proximity to the nearest road. Snowfalls
occur on average between 1-8 times per annum, with village vulnerability increasing with
altitude. High altitude (>2500m) villages such as Thoteng, Letseng-la-Terae and
Mabalane are most vulnerable to prolonged snow cover during the mid- snow season of
July/August. We demonstrate the importance of applying spatio-temporal assessments
on infrequent snow-related hazards in developing mountain regions such as Lesotho,
with implications to reduce livelihood risks through improved disaster preparedness and a
well-informed, focussed emergency response.
11:00 - 11:15
220
Relating avalanche activity to climate change and coupled ocean-atmospheric
phenomena
Sascha Bellaire1, Bruce Jamieson1,2, Grant Statham3
n. 9 foto
Dept. of Civil Engineering, University of Calgary, Calgary, Canada, 2Dept. of
Geoscience, University of Calgary, Calgary, Canada, 3Parks Canada Agency, Banff,
Canada
1
Climate change is evident and long-term changes of the climate system have been
observed. It has been shown that changing atmospheric conditions influence the
formation and evolution of the seasonal mountain snow cover and therefore determine
the avalanche hazard. For this study we analyzed weather data measured at two weather
stations between 1965 and 2012 located in Glacier National Park, British Columbia,
Canada as well as avalanche data from the same region, i.e. along the section of the
Trans Canada Highway located within Glacier National Park. The mean annual air
temperature showed similar trends for the last decades as already found for the Northern
Hemisphere (+0.5 °C Mt. Fidelity, +0.7 °C Rogers Pass). The largest increase of the
monthly mean air temperature was found for the early winter month from November to
January. A decreasing trend of the solid precipitation rate, i.e. more rain events, was
found for the early winter season (October to December) favouring the formation of early
season rain crusts. This might be related to climate change induced warming during the
last decade favouring more weaknesses deep in the snowpack and potentially more
deep slab avalanches. The frequency of natural avalanches within Glacier National Park
did not increase during the last decades, but a trend towards more avalanches in
January and March was found which might be related to the formation of early season
rain crusts and therefore a shift towards deeper instabilities. An increasing frequency of
avalanche activity could be expected during winters associated with La Niña or the cold
phase of the Pacific Decadal Oscillation (PDO). Winters where La Niña and the cold
phase of the PDO are in phase showed higher avalanche activity.
Seehorn
Session
10:15 - 11:45
C5.1b
Past, current and future water, snow and ice availability, use, and management in
mountain regions
11:29 - 11:44
568
Observed timing of spring river discharge and snowfall low-frequency variability over Alps
Matteo Zampieri1, Enrico Scoccimarro1, Silvio Gualdi1
n. 9 foto (troppo
distante)
CMCC Euro-Mediterranean Centre for Climate Change, Bologna, Italy
1
In this work, we analyzed the long-term river discharge measurements of the main Alpine
rivers: Rhine, Danube, Rhone and Po.
The results show a common tendency of anticipating the spring discharge of about 2-to-3
weeks in the last 100 years. We interpret these results using the homogenized
precipitation and temperature observations and reconstructed snowfall and snowmelt
produced within the HISTALP project. Change in the seasonality of precipitation and in
the liquid to solid ratio appear to be the main drivers of this long-term changes. Snowmelt
timing can determine the discharge timing trend computed on shorter scales.
Spring precipitation and snowfall low-frequency variability appear to be related to the
phase of the Atlantic Multidecadal Oscillation, which can explain the abrupt snowfall
reduction observed in the mid 1990s.
Aspen II
Session
13:15 - 14:45
A5.5b
Open alpine cryosphere session
13:45 - 14:00
770
Alpine glacier instabilities: processes and early warning perspectives
Jerome Faillettaz1, Pierre Dalban Canassy1, Martin Funk1
n. 6 foto
1
Michèle
Alpine glacier instabilities are gravity-driven rupture phenomena. Three different types of
instabilities can be identified according to the thermal properties at the ice/bed interface.
In the case of a cold glacier (1), the maturation of the rupture is shown to be associated
with a typical time evolution of surface velocities and seismic activity generated by the
glacier. A prediction of the break-off event is possible by using these precursory signs.
For the other types of instabilities, water plays a key role in the initiation and the
development of the instability. If the ice above the bedrock is partly temperate
(polythermal, 2), the presence of melt water at the interface reduces the basal resistance
of the ice which promotes the instability. No clear and easily detectable precursory signs
could be evidenced in this case, and the only way to infer a possible instability initiation is
to monitor the time and spatial evolution of the thermal regime at the interface. The last
type of instability concerns steep temperate glacier tongues (3) switching for a couple of
days/weeks during the melting season into so called ´´active phases´´ with enhanced
basal motion. In rare cases an ''active phase'' may lead to a major slide off event.
Although the time prediction of such events remains far from being realizable yet, we
could nevertheless identify critical conditions promoting the final instability with a newly
developed numerical modeling including water flow in a subglacial drainage network and
a combined seismological and ice dynamical study performed on Triftgletscher. In the
light of these findings, we will finally discuss how the ongoing global warming may alter
the stability of some Alpine glaciers.
14:00 - 14:15
VAW ETH Zurich, Zurich, Switzerland
627
n. 1 foto
Linking geophysical data with physical properties at the cold Alpine drilling site Colle
Gnifetti
Pascal Bohleber1, Jan Eichler2, Anja Diez2,3, Tobias Binder4, Coen Hofstede2, Ilka
Weikusat2, Dietmar Wagenbach1, Olaf Eisen2
Institute for Environmental Physics, Heidelberg University, Heidelberg, Germany,
Glaciology, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven,
Germany, 3Geophysical Institute, Karlsruhe Institute of Technology, Karlsruhe, Germany,
4
Interdisciplinary Center for Scientific Computing, Heidelberg University, Heidelberg,
Germany
1
2
Colle Gnifetti, constitutes a small scale glacier saddle the Monte Rosa summit range
(4450m asl) expected to provide multi-millenial ice core records. To assist the
identification of climatic signals among multiple ice cores, ground-penetrating radar
(GPR) has been deployed for mapping internal isochrone reflections between the drilling
sites. However, observable internal GPR reflections remained restricted in depth and
were limited roughly to the firn zone (< 30 m). Additional information on internal layers is
available now from seismic surveys carried out in the proximity to an 62 m long ice core
drilled to bedrock. At this location, we combine the geophysical datasets with ice core
properties comprising cm-resolution data (i.e. melt water conductivity, insoluble particle
content, density). For this purpose, information on crystal orientation fabric (COF) was
recently added to the ice core data sets: COF was measured on 22 samples covering the
depth range 2 − 62 m, with an exemplary section (54-55m) of high depth resolution
measurements (8 samples per m). For depths below the firn ice transition, strong
anisotropic COF patterns were revealed. Here we present results from the comparison of
the first COF dataset with the existing ice core properties. We especially focus on a
quasi-harmonic oscillation detected in the high-resolution COF segment in an attempt to
link it to oscillations of the cm-resolution ice core data. With respect to seismic data, the
anisotropy is found to be consistent with propagation velocities from compression and
shear wave data. For GPR, we incorporate the high-resolution COF data into a revised
hypothesis regarding the depth limitation of internal reflections by clutter, hence
demonstrating the benefit of COF information for the interpretation of geophysical data at
an Alpine drilling site.
14:15 - 14:30
1088
Reconstruction of past accumulation rates on Findelengletscher from airborne GPR and
firn cores
Leo Sold1, Martin Hoelzle1, Matthias Huss1, Anja Eichler2, Margit Schwikowski2
Department of Geosciences, University of Fribourg, Fribourg, Switzerland, 2Paul
Scherrer Institute, Villigen, Switzerland
1
The accumulation area of alpine glaciers contains a record of glacier mass balance in the
past. By measuring thickness and density of annual firn layers, past accumulation rates
can be retrieved. We discuss such measurements from 2012 on Findelengletscher,
Switzerland, a large Alpine valley glacier, using several in-situ firn cores that are
analysed with respect to density and thickness of the annual firn layers. Groundpenetrating radar (GPR) has previously been used for a non-destructive assessment of
internal layers in snow, firn and ice. Signal reflections indicate changes in the dielectric
properties of the material, e.g. density changes at former summer surfaces. Conversion
to depth or water equivalent requires the radio-wave velocity that is obtained from the insitu density-depth profiles. The depths of reflectors in the helicopter-borne GPR profiles
are in line with the findings from the firn cores. A distributed data set of past accumulation
rates can thus be obtained by tracking of the reflectors between the firn cores.
Furthermore, we use GPR to reconstruct the annual accumulation on Findelengletscher
since 2007 based on the measurements that have been conducted in 2010, 2011, and
2012. Overlapping GPR profiles in consecutive years allow tracking firn layers over time
and thus provide firn compaction rates. Results are compared with a firn densification
model. We show that in remote areas helicopter-borne GPR is an effective method to
derive several years of past accumulation rates. It benefits but does not depend
exclusively on the time-matched availability of firn cores when overlapping profiles are
mapped in subsequent years.
Wisshorn
Session
13:15 - 14:45
B2.2a
Extreme events under changing climate
13:15 - 13:45
718
Trends in temperature and precipitation extremes analysed from global observational
datasets in comparison to reanalysis and climate model data
n. 6 foto
Markus Donat1,2, Lisa Alexander1,2, Hongang Yang1,2, Jana Sillmann3, Simon Wild4
Michéle
1
Climate Change Research Centre, University of New South Wales, Sydney, Australia,
ARC Centre of Excellence for Climate System Science, University of New South Wales,
Sydney, Australia, 3Canadian Centre for Climate Modelling and Analysis, Victoria,
Canada, 4School of Geography, Earth and Environmental Sciences, University of
Birmingham, Birmingham, United Kingdom
2
Based on newly developed global gridded data sets of climate extremes indices, we
analyse how temperature and precipitation extremes have changed during the past
century. Results are compared across the datasets, as well as to climate extreme indices
calculated from global reanalysis data and climate models.
We find consistent and wide-spread warming trends over much of the globe, as reflected
by e.g. increasing numbers of warm days and nights and fewer cold days and nights,
higher extreme temperature values and longer warm spell durations. Extreme
precipitation indices are characterized by a higher variability than the extreme
temperature indices, and changes are spatially more heterogeneous. However, on global
average we also find a tendency towards stronger precipitation, and larger areas with
significant trends towards wetter conditions than areas with drying trends.
While we find a strong agreement between the different observational datasets, larger
differences are found for some of the reanalysis results, particularly during the presatellite era. For the NCEP1 reanalysis we document spurious values of maximum
temperature which seem to make this dataset unsuitable for the analysis of warm
temperature extremes. We conclude that there is high robustness of the observational
results since the middle of the 20th century, but reanalysis seem suitable for this kind of
global analysis of climate extremes only during the most recent 3 decades when satellite
data are used for assimilation. The ensemble of CMIP5 climate simulations generally
shows a comparable tendency of changes, however there is also a large inter-model
spread.
Aspen II
Session
16:15 - 17:45
A5.5c
Open alpine cryosphere session
16:30 - 16:45
1078
The TEMPS project - the evolution of mountain permafrost in Switzerland
Christian Hauck1, Reynald Delaloye1, Isabelle Gärtner-Roer2, Christin Hilbich1,2, Martin
Hoelzle1, Robert Kenner3, Sven Kotlarski4, Christophe Lambiel5, Antoine Marmy1, Johann
Müller2, Jeannette Noetzli2, Marcia Phillips3, Jan Rajczak4, Nadine Salzmann1, Michael
Schaepman2, Christoph Schär4, Benno Staub1, Ingo Völksch2
Department of Geosciences, University of Fribourg, Fribourg, Switzerland, 2Department
of Geography, University of Zurich, Zurich, Switzerland, 3WSL Institute for Snow and
1
Avalanche Research SLF, Davos, Switzerland, 4Institute for Atmosphere and Climate
Science, ETH, Zurich, Switzerland, 5Geographical Institute, University of Lausanne,
Lausanne, Switzerland
Permafrost occurs in many high-mountain regions of the European Alps. In the context of
anticipated climatic changes, permafrost degradation and associated ground deformation
and instabilities could occur. To evaluate the sensitivity of mountain permafrost to
climatic changes and to assess its future evolution, not only climatic variables such as air
temperature, radiation and timing and duration of snow cover have to be considered, but
also subsurface characteristics such as ground temperature, ice content, porosity or
hydraulic properties.
Permafrost monitoring in the Swiss Alps started only 1-2 decades ago, but currently
comprises a large set of meteorological, geophysical, kinematic and ground thermal
parameters at a large variety of field sites, e.g. within the national permafrost monitoring
network PERMOS. The newly funded SNF-Sinergia project TEMPS (The evolution of
mountain permafrost in Switzerland) analyses and integrates these high-mountain
observations with subsurface model simulations using the coupled heat and mass
transfer model COUP. In combination with results from Regional Climate Model
simulations, TEMPS aims to create plausible evolution scenarios of mountain permafrost
at specific sites and will investigate the interactions between atmosphere and permafrost
focusing on the evolution of ground temperature, ice content and related degradation and
creep processes.
First results will be presented concerning (a) new observation techniques in highmountain permafrost, including thermal, geophysical and kinematic methods, (b)
sensitivity studies with COUP regarding the impact of temperature and precipitation
anomalies on different permafrost landforms and (c) strategies for downscaling and
debiasing RCM output data for permafrost analysis on the station scale at high altitudes.
Schwarzhorn
Session
16:15 - 17:45
A1.2
Reconstructing and understanding the Holocene
16:15 - 16:45
839
Glacier fluctuations in the Holocene and their agreement with other climatic proxies
Olga Solomina1
n. 22 foto
1
Institute of Geography RAS, Moscow, Russian Federation
Michèle
Until very recent time the accuracy of the dating of Holocene moraines was too low to
carefully assess the agreement of glacier fluctuations with other climatic proxies of higher
resolution. Two major achievements: cosmogenic isotope ( 10Be, 26Al, 36Cl ) dating of
glacier landforms (Glasser et al., 2009; Licciardi et al., 2009; Jomelli et al., 2011; Putnam
et al., 2012) and the high resolution glacier activity reconstructions based on multi-proxy
lake sediment analyses, chronologically controlled by AMS dates (Bowerman and Clark,
2011; Larsen et al., 2011) led to a substantial progress in the field of the Holocene glacier
reconstructions. The detailed reconstructions of the upper tree line variations based on
radiocarbon dates and precise cross-dating of ancient wood (Joerin et al., 2008;
Menounos et al., 2009, Agatova, 2012) as well as the archeological artifacts found in the
vicinity or in the glaciers (Nesje et al., 2011) is the third source of important information
on the climate and glacier dynamics in the Holocene.
This paper is an overview of these new findings with the focus on the following questions:
1. What are the regional long-term trends (presumably orbital) in the Holocene glacier
variability? 2. How well these trends agree with other climatic proxies? 3. What are the
periods of major glacier advances in key mountain regions in the Holocene? 4. Do they
agree with the submillennial climatic forcings? 5. What is the scale of advances and
retreats of the glaciers over the Holocene? What is the scale of most pronounced retreat,
when it happened and for what reason? Is it comparable with the glacier recession in the
early 21 century? 6. Is it possible to assess the ice volume changes in the mountains
over the Holocene? How this general assessment agrees with the sea level change
reconstructions?
Sanada I
Session
16:15 - 17:45
C4.5a
Methods and challenges of snow measurements
16:45 - 17:00
368
Field experiments for studying the effects of soot on snow in Finland
Aki Virkkula1, Onni Järvinen2, Antti Aarva1, Niku Kivekäs1, Jonas Svensson1, Heikki
Lihavainen1, Antti Hyvärinen1, David Brus1, Kimmo Neitola1, Outi Meinander1, Riikka
Väänänen2, John Backman2, Gerrit de Leeuw1, Pavla D. Waldhauserová3
Finnish Meteorological Institute, Helsinki, Finland, 2Department of Physics, University of
Helsinki, Helsinki, Finland, 3University of Iceland, Reykjavik, Iceland
1
The Soot on Snow (SoS) project is organized by the Finnish Meteorological Institute and
it is aimed for studying the effects of soot on snow optical properties and melting. The
first experiment was conducted in 2011, the second in 2012, and the third in 2013.
In the first campaign soot particles were produced by burning various organic materials in
a wood-burning stove on a farming field in southern Finland. The smoke was lead
through a pipe, cooled by snow surrounding the pipe, and lead into a chamber on top of
the snow. After the soot production was over, the chamber was removed from the area.
Snow samples were taken from the deposit area and a reference area, to be analyzed for
organic and elemental carbon. The albedo of the snowpack was measured both over the
deposit and the reference area. Snowpack thickness was measured in both areas during
the whole spring. A physical characterization of snow stratigraphy was done a month
after the deposition, including thickness, density, hardness, grain size and shape, and
temperature. In addition, the spectral irradiance at the depth of 20 cm was measured in
the wavelength range 400 - 900 nm. The experiment demonstrated very clearly the
effects of soot on snow: the albedo decreased, the snow grain size, the whole
stratigraphy, temperature profile, and melting rate in the snow pack changed compared
with the reference site.
In 2012 the soot was first acquired from chimney cleaners in Helsinki and blown into a
new chamber laying on snow again in southern Finland. This time the experiment did not
succeed so well because of various reasons, to be discussed. In March 2013 the
experiment will be repeated in Lapland and in addition to soot, volcanic dust from Iceland
will be blown over snow.
17:00 - 17:15
639
Snowflake classification using a 2D video-disdrometer
Samuel Monhart1, Marc Schneebeli1, Alexis Berne1
n. 1 foto
LTE, EPFL, Lausanne, Switzerland
1
Snowflakes fall in a broad range of shapes and densities (needle, plate, column, dendrite
or aggregate to name a few) depending on the environmental conditions (mainly
temperature and humidity). The 2D video-disdrometer (2DVD hereafter) is able to provide
2D pictures of the falling hydrometeors from 2 perpendicular views. Such detailed
information is relevant to study the microstructure of precipitation in general and of
snowfall in particular. A first valuable step is the ability to classify the snowflakes (to
compare with polarimetric classification for instance). The main objective of the present
contribution is to propose an innovative approach based on supervised classification to
assign 2DVD measurements (1-min resolution) to different snowflake classes. A large
data set corresponding to 2 winter seasons and collected in the Swiss Alps is used. After
careful filtering and rematching of the falling particles sampled by a 2DVD, various
descriptors related to the respective distributions according to height, width and fall
speed are calculated at each (1-min) time step. A training set is then built by manually
classifying 2DVD data, so that the proposed algorithm (based on linear discriminat
analysis) can be "trained" to classify time steps as a function of the descriptors. 5 classes
have been defined: large-aggregate-like, aggregate-like, dendrite-like, graupel-like and
small particles. The comparison of the manual and automatic classifications on a set of
about 190 (1-min) time steps covering all the 5 classes shows the good quality and
reliability of the proposed automatic classification approach. This approach opens new
opportunities for the comparison between the classification derived from measurements
collected by the 2DVD and a near-by polarimetric radar, as well as for the investigation of
snowfall microphysics at high-temporal resolutions.
17:15 - 17:30
1157
Evolution of crystal orientation in snow during temperature gradient metamorphism
Maurine Montagnat1, Fabienne Riche2, Martin Schneebeli3
n. 3 foto
LGGE - CNRS - UJF, St Martin d'Hères, France, 2WSL – Institute for Snow and
Avalanche Research SLF, Davos, Switzerland, 3WSL – Institute for Snow and Avalanche
Research SLF, Davos, Switzerland
1
The physical properties of snow are tied to its microstructure. Especially for the slow,
plastic deformation of snow and firn, the crystal orientation is an important factor in
addition to the geometry of the ice matrix. While micro-computed tomography measures
precisely the snow microstructure, it gives no information about the orientation of the ice
crystals. In this study, we applied a temperature gradient of 40 Km -1 to large blocks of
undisturbed decomposed snow and sieved snow during three months. The snow
temperature at the sampling location was -20°C. Two closely spaced snow samples were
taken before the experiment, then every week during the first month and afterwards
every month. From each sampling, one sample was analyzed by micro-computed
tomography and the other was used for thin sections. The orientation of the c-axis was
measured in the thin sections using an Automatic Ice Texture Analyser. The results show
that not only the shape and size of the crystals change, but also their orientation. In our
experiment, the evolution of the orientation of the crystals from a predominantly vertically
oriented c-axes toward a girdle-type fabric is affected by the density and the pore
structure.
12. Jul. 2013
Sanada II
Session
08:15 - 09:45
B6a
Solar ultra-violet radiation in mountainous regions
08:15 - 08:45
459
Effective solar UV albedo retrieval to reconstruct the areal mean snow depth
Luca Egli1, Julian Gröbner1, Gregor Hülsen1, Christoph Marty2
n. 4 foto
Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center,
Davos-Dorf, Switzerland, 2WSL – Institute for Snow and Avalanche Research SLF,
Davos-Dorf, Switzerland
1
Solar ultraviolet radiation measurements in a spectral range between 320 - 360 nm are
strongly influenced by the reflective surface of the surrounding terrain. The effective UV
albedo is mainly determined by the reflectance of snow cover in an area of about 40 km,
which roughly corresponds to the dimension of a snow micro climatological region in the
Swiss Alps. In particular during snow ablation, the melt out patterns significantly change
the effective albedo due to the decrease of snow covered area (SCA). In this study, the
temporal evolution of the albedo in the area of Davos during the season 2008 and 2009
is estimated using continuous spectral global solar UV measurements in the valley
bottom of Davos and a radiative transfer model. The temporal course of the melt-out
patterns during the ablation period is simulated according to previous studies using a
generated gamma and lognormal distribution and the concept of spatially uniform snow
depletion rates. The so modelled SCA are converted to effective albedo using broadband
UV albedo point measurements at Weissfluhjoch above Davos. We show that albedo
observation during the entire ablation period and monte-carlo based SCA simulations
allow reconstructing the statistical properties of the snow cover such as the integral mean
snow depth at the peak of winter. We argue that existing long-term measurements of
solar UV in mountainous regions may help to support area wide investigations in snow
climatology.
08:45 - 09:00
269
Effective albedo retrieval from spectral UV measurements using 3-D modelling of
inhomogeneous topography
Philipp Weihs1, Julian Gröbner2, Luca Egli2, Gregor Hülsen2, Yves Bühler3
Institute of Meterology, Water, Atmosphere, Environment/University of Natural
Resources and Life Sciences, Vienna, Austria, 2Physikalisch-Meteorologisches
Observatorium Davos, World Radiation Center, Davos, Switzerland, 3WSL – Institute for
Snow and Avalanche Research SLF, Davos, Switzerland
1
Solar ultraviolet radiation is strongly influenced by highly reflective surfaces such as snow
covered terrain. The effective albedo retrieved from measurements using 1-D radiative
transfer modeling assumes a homogeneous flat surface, which is an approximation not
valid in complex mountainous regions. Solar UV Measurements between 2008 and 2012
at Davos and Weissfluhjoch are used to retrieve the effective albedo from 1-D and 3-D
radiative transfer modelling. The study shows that solar UV radiation measurements
performed in the valley of Davos, Switzerland show a distinct diurnal variation of the
retrieved 1-D effective albedo, even though surface conditions remain constant over the
day. Using state-of-the-art 3-D modelling of the surrounding area, we demonstrate that
the solar UV radiation measured in the valley floor of Davos is significantly influenced by
the surrounding topography. Specifically, we show that the 1-D effective albedo retrieved
by 1-D modelling is not appropriate under highly reflective surfaces in a complex
mountainous topography and shows a diurnal variation of more than 20%. We
demonstrate that for a comprehensive characterisation of the factors affecting the UV
radiation field in highly reflecting mountainous terrain it is essential to take into account
the topography of the surrounding area.
Sanada I
Session
08:15 - 09:45
C4.5b
Methods and challenges of snow measurements
09:00 - 09:15
1015
Comparison of methods for precipitation and meteorological measurements at Col de
Porte (France) and their use for evaluating snowpack models
n. 1 foto
Yves Lejeune1, Bernard Lesaffre1, Jean-Michel Panel1, Thomas Condom2, Romain Biron2,
Jean-Paul Laurent2, Samuel Morin1
Météo-France - CNRS, CNRM - GAME, CEN, St Martin d'Heres, France, 2CNRS – UJF
Grenoble – IRD – G-INP, LTHE, Grenoble, France
1
Meteorological measurements, in particular precipitation and incoming radiation, are
notoriously difficult to carry out in mountain environments. Here we present methods
employed to circumvent issues associated to snow deposition on sensors and
precipitation gauge issues such as snow undercatch at the experimental field site Col de
Porte, 1325 m altitude, located in the French Alps near Grenoble. The site has a long
history of over 50 years of meteorological and snow observations, and serves as a
platform hosting several instruments under development or test for precipitation or other
snow-related measurements. This includes continuous operation of one GEONOR
precipitation gauge featuring a heated collection ring and a dedicated anemometer at the
same vertical level and within 2 m horizontal distance of the inlet for wind-speed
corrections of snow precipitation, two 2000 cm2 “PG2000” instruments (one of them has
an heated inlet). Other precipitation instruments such as disdrometers are also tested.
Automatic snow depth monitoring is carried out at various locations in the experimental
field. Weekly manual observations of the physical properties of snow on the ground
(several snow cores for SWE measurements) complement the suite of automated
measurements. Building on this long-standing expertise, the site intends to contribute to
the ongoing WMO Solid Precipitation Intercomparison Experiment (SPICE).
The presentation will highlight the main characteristics of the data quality insurance
policy (including corrections for wind-induced undercatch in precipitation gauges) at Col
de Porte, and show the results of the in-site intercomparison between different
automated precipitation sensors. It will also show how the hourly record of meteorological
data gathered at col de Porte is used together with snow evaluation data to assist in the
development and evaluation of snowpack models of various levels of complexity, and
how such models are in turn used to evaluate the consistency of the meteorological
observations.
09:15 - 09:30
290
n. 2 foto
Snow fall measurement at Rikubetsu in Japan, a site for SPICE
Naohiko Hirasawa1, Hiroyuki Konishi2
National Institute of Polar Research, Tokyo, Japan, 2Osaka Kyoiku University, Osaka,
Japan
1
Rikubetsu locates in East Hokkaido, the northern part of Japan, where the smaller
amount of snowfall is usually measured with the coldest climate of Japan. In 2011/12
winter, our measurement with LPM, a disdrometer manufactured by Thies Clima,
observed totally approximately 120 mm per the three winter months (December to
February). The snow fall amount was estimated using our original algorism to convert
from measured raw data to calibrated data of snow fall amount. The ordinal observation
by raingauge-type instrument operated JMA at a site about 2.5 km away from our site
reported approximately 60% in the amount of our measurement, indicating the loss of
measurement is not negligible. The problem gets serious more in higher latitudes and
polar region because of high frequency of weak snowfall associated with the colder
condition.
We have ever operated several kinds of disdrometer, ceilometer and tethered balloon to
obtain temperature and moisture condition at this site. In the last year, we have finished
the construction of DFIR and have preliminary carried out observation with it while the
integration of instruments has currently been continued. At first, this presentation will give
information on characteristic of snowfall and climate of Rikubetsu through the past data,
including our activity. Secondary, the geographical characteristic of it will be shown as a
site for SPICE as well.
09:30 - 09:45
1075
Reference measurements at Weissfluhjoch (Switzerland) for the WMO/CIMO SPICE
Project
Yves-Alain Roulet1, Jean-Marc Aellen1, Serge Brönnimann1, Charles Fierz2, Christoph
Marty2, Marc Ruesch2
MeteoSwiss, Payerne, Switzerland, 2WSL-Institut für Schnee- und Lawinenforschung
SLF, Davos, Switzerland
1
SPICE (Solid Precipitation Intercomparison Experiment) is a WMO/CIMO
intercomparison of instruments and systems for the measurement of solid precipitation.
One of the main objectives is the assessment of a wide range of instruments under
various climate. For that purpose, around 15 sites are equipped worldwide and
configured according to standards defined within the project, in order to allow comparison
between the sites. The experiment started in December 2012 and is meant to last 2
years. At Weissfluhjoch (Switzerland) a site is being set up to provide reference
measurements for the Alpine climate. The paper will present the site and its first results.
Sanada II
Session
10:15 - 11:45
B6b
Solar ultra-violet radiation in mountainous regions
10:45 - 11:00
585
UV measurements at mountain sites
n. 3 foto
Gregor Huelsen1, Julian Groebner1, Henri Diémoz2, Mario Blumthaler3, Ricardo Sánchez4,
Ezequiel Villegas5
X info!
1
Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Davos,
Switzerland, 2Agenzia Regionale per la Protezione dell'Ambiente della Valle d'Aosta,
Valle d'Aosta, Italy, 3Medizinische Universität Innsbruck, Innsbruck, Austria, 4Servicio
Meteorológico Nacional, Buenos Aires, Argentina, 5Servicio Nacional de Meteorologia e
Hidrologia del Peru, Lima, Peru
Solar UV measurements are recorded at many mountain sites across the world. These
measurements deliver important information for climatology and environmental studies.
Because of the increase of mountaineering activities to remote mountain locations and
skiing activities in the mountains, the UV measurements serve also as important health
warning. Solar UV measurements from the European alpine stations at Davos in
Switzerland, the Italian region Valle d'Aosta and the UV measurement network of Austria
are distributed across the Alps. The selected measurement sites are representative for
alpine resorts and cities with many activities both in summer and winter seasons. The
altitudes range from 570 m a.s.l. to 3500 m a.s.l.. In the southern hemisphere UV
networks in Argentina and Peru provide measurements across the Andes at altitudes up
to 4500 m a.s.l.. The UV data have been analysed for the last decade. The UV level can
reach values up to 13 in the Alps at high altitudes compared to 9 in the low valleys. Of
special interest are the touristic summer months for mountaineering in July-September in
the Alps and May-September in the Andes (winter). The high season for skiing activities
in the Alps is from December till April, where in addition the high reflectivity of snow
increases the human exposure. At the high altitude sites the skiing extents into the
summer season. At the end of April, the UV Index can be as high as 11 at Plateau Rosa
(3500 m a.s.l.) and 8 at La Thuile (1640 m a.s.l., IT). In the summer season, the UV
Index at La Thuile can reach values of 9 units. As a last step the erythema weighted UV
data have been converted to a VitaminD weighted dataset. This analysis facilitates the
mountaineers to weight the harmful against the beneficial effects of UV radiation.
Sanada I
Session
10:15 - 11:45
C4.5c
Methods and challenges of snow measurements
10:15 - 10:45
731
Variability in snow depth influencing sampling strategies
Steven Fassnacht1, Juan Igancio Lopez-Moreno2, Graham A. Sexstone3, Evan J.
Blumberg4, Amir H. Kashipazha1
ESS-Watershed Science, Colorado State University, Fort Collins, United States,
Pyrenean Institute of Ecology (Spanish Research Council), Zaragoza, Spain, 3EASCWatershed Science, Colorado State University, Fort Collins, United States,
4
Geosciences, Colorado State University, Fort Collins, United States
1
2
As we transition to improved remote sensing of snowpack properties we continue to rely
heavily on manual measurements to provide ground truth data. The collection of manual
snowpack data has been ongoing for a century, yet the representivity of measurements is
still uncertain. We collected snow depth measurement across a 1 km2 area about five
snow telemetry stations in four Western United States. Data were collected at one of
these locations on or about May 1st for five years. The data are approximately 200 sets
of measurements. Each measurement set contained multiple measurements and was
assumed to be representative of that particular location. The location was location with a
geographical positioning system and assumed to represent a single digital elevation
model (DEM) pixel (30-m resolution). The DEM data were used to derive a series of
terrain variables for each measurement location, including slope, aspect, curvature,
clear-sky solar radiation. Land cover and canopy density data were also extracted for
each measurement location. The terrain and vegetation data were used to assess 1) the
spatial distribution of mean snow depth, 2) the distribution of the variation in snow depth
(standard deviation and coefficient of variation per measurement location), and 2) the
number of individual measurements required to reduce uncertainty at each location.
There were similarities among stations for each snow statistic (mean, standard deviation
and coefficient of variation). However, there was limited similarity between the different
snow statistic s. There was a reasonable amount of inter-annual consistency for each
snow statistic at the station with five years of data.
11:00 - 11:15
801
Measuring liquid and solid precipitation with a modified tipping bucket
Reinhard Fromm1, Reinhold Steinacker2
Institute of Natural Hazards, Austrian Research Centre for Forests, BFW, Innsbruck,
Austria, 2Department of Meteorology and Geophysics, University of Vienna, Vienna,
Austria
1
Automated measurements of liquid and solid precipitation are a demanding task.
Therefore a standard tipping bucket is combined with an open-top collecting vessel. The
vessel is filled with a mixture of water and an antifreeze fluid. Solid and liquid
precipitation is collected in the vessel and induces an overflow, which is measured by the
tipping bucket and recorded by the data logger. A thin oil film avoids evaporation from the
fluid surface. No heating is necessary for this low-cost device, but liquid and solid
precipitation can be measured.
The different thermal properties of water, antifreeze fluid and the vessel, as well as the
temporal changes of the concentration of the mixture are considered for the
determination of the real amount of precipitation. Ordinary differential equations describe
the behavior of the depth of water and antifreeze fluid, the geometry of the vessel and the
calculated precipitation.
More specifically, a decrease of the temperature (above +4°C) originates a lower fluid
level. Subsequent precipitation fills-up the vessel before an overflow occurs. Otherwise,
warming may create an overflow whether precipitation occurred or not. An algorithm was
developed, which is able to deal with these circumstances.
Precipitation data were collected with the modified tipping bucket at different sites located
in alpine and pre-alpine terrain. The results are compared with data from heated
precipitation gauges and snow pillows.
11:15 - 11:30
1270
Merging observations, remote sensing, and modeling to delineate multi-scale snow
patterns
Anna M. Wagner1, Christopher A. Hiemstra1, Matthew Sturm1
Cold Regions Research and Engineering Laboratory (CRREL), Hanover, United States
1
The location of deep and shallow areas of snow tends to repeat from one year to the
next. Topography, land cover, and weather interactions produce persistent patterns that
change slowly compared with seasonal cycles of snow accumulation and melt. While
mean snow depth varies from year to year in most landscapes, relative snow depth
differences remain fixed. When snow patterns can be identified, understood, and
classified using ground observations, remote sensing, and/or models, an untapped
potential exists to expand and improve snow distribution assessments and predictions.
The repeatability of snow patterns at three nested scales has been demonstrated on
Alaska´s North Slope for the winters of 2010-2012. At the finest scale, snow
measurements occurred on a 1km2 study area grid. At the intermediate scale, a 6km2
area encompassing the 1km2 area was sampled by collecting measurements along 100
m lines scattered randomly in space and orientation across the area. At the coarsest
scale, a 21 km2 was sampled using 36 randomly distributed 200-m long lines distributed
over the entire area. For the same areas, we also collected a sequence of high-resolution
WorldView-2 and Quickbird satellite imagery for the 2011 melt sequence. We also
simulated the snow distribution in detail using SnowModel, which uses topography, land
cover, and meteorological data to realistically simulate snow accumulation, redistribution,
and ablation over the domain.
The three independent time series show striking repeatability in snow depth patterns at
all scales and among all years. For 2011, when the imagery dataset is largest, the spatial
agreement between satellite-derived snow cover and SnowModel is remarkable. Our
results indicate that there is a high degree of fidelity in snow patterns for this class of
snow, and that this fact could be used to a much greater degree in understanding and
predicting snow cover distribution and properties.
11:30 - 11:45
398
Experiences from 60 years of measuring snow accumulation on two Alpine glaciers
Andrea Fischer1, Kay Helfricht2
Institute of Interdisciplinary Mountain Research, Austrian Academy of Sciences,
Innsbruck, Austria, 2alpS Centre for Climate Change Adaptation Technologies, Innsbruck,
Austria
1
Measuring the accumulation of snow on Alpine glaciers and relating it to measurements
of precipitation always has been a challenge, and so far, a perfect monitoring set up has
not been developed. Within the basin of Hintereisferner, snow accumulation and
precipitation has been measured at four snow pits and six rain gauges for six decades.
The precipitation measured at the rain gauges correlates with a mean Pearson coefficient
of 0.77 with relations between 1.4 and 2.2 between the specific rain gauges. The
standard deviation of accumulation is between 21 and 26 % of the mean with no
significant dependence on distance or elevation. The standard deviation of the SWE in
the snow pits is 28% to 35%. Comparing snow pits and rain gauges, the mean Pearson
correlation coefficient is 0.58, the correlation between the specific snow pits is higher
(0.64).
At Hintereisferner multi-temporal LiDAR data of five accumulation seasons exist. The
surface elevation changes can be transferred into SWE using a linear regression
between snow depth and snow density.
The mean Pearson correlation coefficient between accumulation from LiDAR data and
precipitation measurements at the rain gauges is 0.62. Mean multiplication factors
between measured precipitation at the rain gauges and mean accumulation derived from
LiDAR data ranging from 3.0 and 1.7 with a mean standard deviation of 0.4.
On Jamtalferner, the snow water equivalent measured on the glacier is compared to
automatic and observer-based snow measurements as well as the precipitation
measured by rain gauges. During winter, automatic and observer measurements can
differ significantly.
For future monitoring strategies, a combination of continuous snow depth, point SWE and
spatially distributed snow depth measurements seems be most effective to get an reliable
estimate of SWE accumulated in the basin.
Wisshorn
Session
13:15 - 14:45
B2.2e
Extreme events under changing climate
13:45 - 14:00
576
Dependence of future changes in extreme winter precipitation on stratospheric vertical
resolution and model height in CMIP5 models
n. 5 foto
Robin Clark1, Simon Brown1
Met Office Hadley Centre, Exeter, United Kingdom
1
Excessive autumn and winter rainfall over northern Europe often results in flooding and
associated economic and societal impacts. Over the coming century, most climate
models predict increases in both the intensity and frequency of such events.
However, recent research suggests, a strong dependence in projections of winter rainfall
on the handling of stratosphere processes by climate models. Using data from upto 20
CMIP5 models with a variety of stratospheric representations we investigate this
dependence and its effect on future changes in extreme rainfall.
We find there is indeed a significant effect on the magnitude of changes but with less
clear implications on any geographical shift in rainfall patterns.
14:00 - 14:15
n. 3 foto
957
Projections of extreme precipitation events in regional climate simulations for Europe and
the Alpine region
Jan Rajczak1, Pardeep Pall2, Christoph Schär1
Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland, 2Lawrence
Berkeley National Laboratory, Berkeley, United States
1
Regional climate models from the ENSEMBLES project are analyzed to assess projected
changes in 21st century heavy and extreme precipitation over Europe. A set of 10 RCMs
with a resolution of 25 km is considered, driven by 6 GCMs under an A1B scenario. The
diagnostics include basic precipitation indices (mean, frequency, intensity and
percentiles) and application of generalized extreme value theory for return-periods up to
100 years. Changes between present (1970-1999) and future (2070-2099) conditions are
presented for Europe, and in detail for the Alps.
On the European scale, projections show increases (decreases) in mean and frequency
in northern (southern) Europe, with a seasonally oscillating pattern. Changes in extremes
exhibit similar patterns, but increases reach much further south. For instance, during
spring and fall, much of the Mediterranean is projected to experience decreases in mean,
but increases in heavy precipitation. Thus, changes in mean and extremes may show
different signals.
The inter-model spread is partly attributable to a GCM-dependent clustering of the
climate-change signal, but also affected by RCM uncertainties, particularly summer.
Despite these uncertainties, many projected changes are statistically significant and
consistent across models. For instance, for the Alps, many models project significant
intensifications of heavy events in fall.
14:15 - 14:30
941
Changes in European summer temperature variability revisited
Christoph Schär1, Erich M. Fischer1, Jan Rajczak1
ETH Zurich, Institute for Atmospheric and Climate Science, Zürich, Switzerland
1
In the recent decade, a sequence of unprecedented European heatwaves has been
observed, including the Great European Heatwave of 2003 and the Great Russian
Heatwave of 2010. It has been argued that some of these events are difficult to explain,
even when the mean observed warming of the last decades is accounted for, and it has
been suggested that variability increases on interannual to daily timescales might
contribute to past and future changes in heatwaves. More specifically, climate models
have projected increases in summer temperature variability in response to anthropogenic
greenhouse gas forcing, and studies have detected variability trends in observational
records.
Here we provide a review and a reassessment of projected variability changes. Based on
an unprecedented set of global and regional climate models from the ENSEMBLES
project, we assess the robustness of projections on interannual to daily time scales. In
comparison to previous analyses using PRUDENCE simulations, we find a more diverse
climate change signal for interannual summer temperature variability and a clear
dependence upon present-day model performance. Models that realistically represent
present-day variability tend to consistently project increasing interannual variability at the
end of the 21st century. We demonstrate that the partitioning of latent and sensible heat
fluxes controlled by soil moisture is crucial to understand the projected changes across
the multi-model experiment. The projected increase in daily summer temperature
variability is more robust and consistently simulated by all models. Likewise, all models
consistently project reduced daily temperature variability in winter. Thus, it is a robust
signal across the entire ensemble that in summer and south-central Europe hot extremes
warm stronger than the mean, and in winter and northern Europe cold extremes warm
stronger than mean temperatures.
Sanada I
Session
13:15 - 14:45
C4.2a
Forest-snow interactions
13:15 - 13:45
1227
Multi-scale observations of snowpack-ecosystem feedbacks: identifying tipping points in
forest response to climate change in the Western U.S.
n. 3 foto
Noah Molotch1, Ernesto Trujillo1, Leanne Lestak1
Institute of Arctic and Alpine Research INSTAAR, University of Colorado, Boulder,
United States
1
New remote sensing and in situ measurement capabilities afford improved understanding
of distributed ecohydrological processes in mountainous regions. In this regard,
distributed ecohydrologic instrument clusters allow us to observe micro-scale variability in
snow-vegetation interactions while remotely sensed data allow to observe integrated
ecosystem-scale response to water availability. Instrument clusters deployed in the
Central and Southern Rockies and the Sierra Nevada reveal the dominant role of
vegetation in controlling timing and magnitude of snow accumulation and snowmelt.
Vegetation structure largely controlled the distribution of snow accumulation with 29%
greater accumulation in open versus under-canopy locations. Snow ablation rates were
diminished by 39% in under-canopy locations, indicating increases in vegetation density
act to extend the duration of the snowmelt season. Similarly, differences in climate
altered snow-season duration, snowmelt infiltration and evapotranspiration.
Commencement of the growing season was coincident with melt-water input to the soil
and lagged behind springtime increases in air temperature by 12 days on average.
Similarly, the timing of peak soil moisture was highly dependent upon snow ablation.
Analysis of remotely sensed vegetation greenness data reveals a coherent signal with
regard to these plot-scale measurements. Observations of forest greenness from polar
orbiting satellites indicate strong forest and understory growth dependencies associated
with snow accumulation and snowmelt. Forest sensitivity to energy availability is also
evident in the satellite record whereby anomalously low snow accumulation combined
with anomalously high potential evapotranspiration result in anomalously low forest
greenness. Examples of these dependencies will be presented based on the 2012
drought in the Southwestern US. These relationships indicate that the sensitivity of
ecosystems to changes in climate is heavily dependent on snowpack processes. Given
potential future changes in the hydroclimatology of mountainous regions, the results of
these multi-scale measurements may identify tipping points regarding ecosystem
responses to water availability across gradients in physiography.
Aspen II
Session
16:15 - 17:45
A5.2
The response of glaciers to climate trends and climate variability: modern
observations, past reconstructions, and scale dependence
16:15 - 16:30
473
A 1600 year history of Alpine glacier equilibrium line altitude inferred from glacier length
records
n. 5 foto
Martin Lüthi1
VAW Glaciology, ETH Zurich, Zurich, Switzerland
1
Michèle
16:30 - 16:45
A new history of glacier equilibrium line altitude (ELA) for the time span 400-2010 is
inferred from the combined interpretation of length change records of seven glaciers from
the Alps with help of a macroscopic model of glacier dynamics. This history is a proxy for
summer temperature, and is fully independent of other instrumental or proxy data. The
temperature record thus obtained bears close similarity to a tree-ring based
reconstruction of central European summer temperature, and to a multi-proxy
temperature history. The glacier record shows a prominent low-ELA (cold) phase around
1330, corresponding to rapid glacier advance, which is absent in the other records.
The reconstructed ELA history is closely correlated to solar irradiance between 18001950, but shows significantly warmer temperatures after 1950. Furthermore, the
macroscopic glacier models yields glacier volume changes, and thus one major
component of the summer river discharge.
524
Climatic attribution of mountain glacier fluctuations
Andrew Mackintosh1, Brian Anderson1, Sam Dean2, James Renwick3, Andrew Lorrey4,
Ruzica Dadic1
Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand,
NIWA, Wellington, New Zealand, 3Geography, Environment and Earth Sciences, Victoria
University of Wellington, Wellington, New Zealand, 4NIWA, Auckland, New Zealand
1
2
Observed mountain glacier retreat during the late 20th and early 21st centuries is
considered to be one of the clearest signals of anthropogenic climate change. However,
few formal attribution studies have been carried out, and in several places (e.g. New
Zealand, the Karakorum), some glaciers gained mass and/or advanced during this
period. We develop a methodology for attributing changes in glaciers to climate
processes, whether it be natural variability in the climate system (e.g. ENSO) or
anthropogenic climate change. Multiple simulations with a regional-scale Energy Balance
Model (EBM) show that temperature change was the most important climatic variable
driving the glacier mass balance increase during the period 1980-2005, and that other
variables (precipitation, cloudiness, wind, etc) had a smaller influence. Using a suite of
CMIP5 climate models in conjunction with the EBM, we show that the advance of glaciers
in New Zealand occurs during cool periods associated with El Niño events and/or
significant equatorial volcanic eruptions. These cause anomalous southerly atmospheric
circulation in the New Zealand region, bringing colder than average temperatures to the
Southern Alps. It is demonstrated that for this period and this region, the signal of
anthropogenic greenhouse gas driven warming is overwhelmed by the ENSO/volcanic
driven variability. We suggest that our method could be applied more widely, and might
be useful in distinguishing between the anthropogenic and natural climate influences on
glaciers in other mountain ranges.
Sanada I
Session
16:15 - 17:45
C4.2b
Forest-snow interactions
16:45 - 17:00
675
Soil C and N response to changes of winter precipitation in a subalpine forest ecosystem,
NW Italy
n. 2 foto
Davide Viglietti1, Michele Freppaz1, Gianluca Filippa1, Ermanno Zanini1
Laboratorio Neve e Suoli Alpini and NATRISK Research Centre on Natural Risks in
Mountain and Hilly Enviroments, Università degli Studi di Torino, Grugliasco (TO), Italy
1
Among the potential effects of climate change on subalpine forest ecosystems during the
winter season, of particular interest are the shift of the snowline toward higher altitude
and the increase in frequency of rain events on the snowpack. We present the
implementation of a new, mid-to-long term study site located in a forest stand (Larix
decidua), at 2020 m a.s.l., in Piedmont (NW-Italy). From 2009 till 2011 we examined the
soil physical characteristics (temperature and moisture), and the soil and soil solution
chemistry (different C and N compounds and their changes in time) after the simulation of
late snowpack accumulation and rain on snow events. A late snowpack accumulation
determined a stronger effect on soil thermal and moisture regimes than rain on snow
events. Also the soil chemistry was significantly affected by late snowfalls simulation:
although microbial carbon and nitrogen were not susceptible to the induced soil freezing,
more labile soil carbon and nitrogen forms (DOC and DON) and inorganic nitrogen
increased when the soil froze. The response of soil solution was not simultaneous with
soil and was shifted to spring and summer seasons, when an increase of DON and NO 3occurred. This study highlights the potential N loss in subalpine forest soils under
changing environmental conditions driven by a changing climate.
17:00 - 17:15
LS-1
n. 5 foto
17:15 - 17:30
Snow avalanches in forested terrain: Potential changes in frequency and magnitude in a
changing environment
Presenter: Michaela Teich
672
n. 2 foto
Influence of soil moisture and temperature on snow gliding and loading under two
different forest stands
Davide Viglietti1, Margherita Maggioni2, Ermanno Zanini2, Freppaz Michele2
Laboratorio Neve e Suoli Alpini and NATRISK Research Centre on Natural Risks in
Mountain and Hilly Enviroments, Università degli Studi di Torino, Grugliasco, Italy,
2
Laboratorio Neve e Suoli Alpini and NATRISK Research Centre on Natural Risks in
Mountain and Hilly Enviroments, Università degli Studi di Torino, DISAFA – Chimica
Agraria e Pedologia, Grugliasco, Italy
1
The presence of a thick snowpack could interfere with forest stability, especially on steep
slopes with potential damages for young and old stands. The study of snow gliding in
forests is rather complex because this phenomenon could be influenced not only by
forest features, but also by snow/soil interface characteristics, site morphology,
meteorological conditions and snow physical properties. Our starting hypothesis is that
different forest stands have an influence on the snowpack evolution and on the
temperature (Ti) and moisture (Mi) at the snow/soil interface, which subsequently could
affect snow gliding processes and snow forces. The aim of this work is therefore to
analyse the snowpack evolution and snow gliding movements under different forest
covers, in order to determine the snow forces acting on single trees. The study site is
located in a subalpine forest in Aosta Valley (NW-Italy) and includes two plots with
different tree composition: Larch (Larix decidua) and Spruce (Picea abies). The plots
were equipped with moisture and temperature sensors placed at the snow/soil interface
and glide shoes for continuous monitoring of snow gliding. The recorded data, collected
during two subsequent winter seasons (2010 and 2011), were related to periodically
monitored snowpack and snow/soil interface properties. The snow forces on trees were
analytically calculated either from snowpack data and site morphology or also from
measured snow gliding rates.
Different snow accumulations were observed under the two different forest stands, with a
significant effect on Ti and Mi. The highest snow gliding rates were observed under Larch
and were related to rapid increases in moisture at the snow/soil interface. The calculated
snow forces were generally lower than the threshold values reported for tree uprooting
due to snow gliding, as confirmed by the absence of observed damages of tree damages
in the study areas during the monitoring period.
17:30 - 17:45
n. 3 foto
446
Energy dissipating effect of forests on the flowing avalanches - numerical simulation over
the terrain of Makunosawa valley, Myoko, Japan
Yukari Takeuchi1, Koichi Nishimura2, Abani Patra3
Tohkamachi Experimental Station, Forestry and Forest Products Research Institute,
Tohkamachi, Japan, 2Graduate School of Environmental Studies, Nagoya University,
Nagoya, Japan, 3Department of Mechanical and Aerospace Engineering, The University
at Baffalo, Baffalo, United States
1
Energy dissipating effect of forests on the flowing avalanches is considered to depend on
such as type and scale of the snow-avalanches, kinds, ages, stem diameters, and stand
density of trees consisting of the forests, and topographies. But, the relationships among
them have not been investigated. Then, the forest effects on the disaster reduction for
avalanches have been known empirically but are not known quantitatively. The largescale dry slab avalanche occurred in the Makunosawa valley in Myoko in February, 2008
and damaged many trees. It was found that the avalanche seemed to stop in the forest
and not pass through the forest. Then we could obtain a dataset of an avalanche with
forest damage.
In this study, avalanche flow was simulated over the terrain of the Makunosawa valley
using the numerical model TITAN2D, in order to verify the effect of forests on reducing
velocity and stopping the avalanche of the Makunosawa valley. In the simulations, forest
was distinguished from open area without forest by giving the larger bed friction angle.
The bed friction angle were regarded as 25 degrees in the forest and 13 - 14 degrees
without forest through trial and error according to the actual position of the farthest reach
of avalanche, avalanche paths and avalanche velocity estimated from the bending stress
of the broken trees. In result of the simulation, if the forest had not existed, the avalanche
might have reach 200 m farther than the actual reach in the forest. The distinct effect of
forest was shown.