ABSTRACTS
CIRMOUNT SESSIONS AGU 2012
Global Environmental Change (GC)
TALKS
Session title: Geomorphology, Ecology, and Climate Coupling in Mountain
Environments
Spatiotemporal characteristics of climatic forcing of erosion – examples from the southern Central
Andes and the Himalaya
Bodo Bookhagen1, Manfred R Strecker2
Dept Geography, UC Santa Barbara, Santa Barbara, CA, United States.
2
Earth and Environmental Sciences, University of Potsdam, Potsdam, Germany.
1
The windward flanks of the southern Central Andes and the Himalaya are characterized by steep climatic,
tectonic, and vegetation gradients. In these regions, orographic rainfall causes some of the wettest places
on Earth that are closely linked with pronounced runoff and erosion. However, the higher-elevation flanks
of both orogens become progressively drier, until arid conditions are attained in the orogen interiors (i.e.,
the Tibetan and Altiplano-Puna plateaus). Some of the world’s largest rivers with high sediment loads
emerge from these mountain belts, and understanding the relation between climate and erosion is key in
predicting mass fluxes, assessing the effects of climate variability, and long-term climate forcing of
erosion on landscape evolution in these tectonically active mountain belts. Here, we present the
spatiotemporal effects of climatic gradients on erosion and mass fluxes. We rely on new sedimentary
archives, digital topography, and cosmogenic nuclide basin-wide erosion rates from the Andes (n=50) and
the western Himalaya (n=30).
We make three key observations that underscore the importance of climatic parameters on the voracity of
surface processes in both areas. (1) First-order spatial erosion patterns can be explained by a simple
specific stream power (SSP) approach. Importantly, we explicitly account for discharge by routing highresolution, satellite-derived rainfall downstream. This is important as the steep climatic gradient of both
orogens results in a highly nonlinear (and non-power law) relation between drainage area and discharge,
one of the key assumptions for deriving energy expenditure in fluvial systems. This simple, but robust
approach allows us to compare similarly steep catchments from the wet windward sectors along the flanks,
with the dry internal parts of the orogens. (2) The derived relation between SSP and basin-wide erosion
rates indicates that erosion (E) scales with E ~ SSP2 on cosmogenic-nuclide time scales. (3) The use of
late Pleistocene and Holocene sedimentary archives (lacustrine sediments related to landslide damming of
river valleys) from both regions furnishes valuable information on the temporal variation of erosion rates.
These records reveal that the high-relief arid sectors of both environments, which are characterized by
low present-day and millennial-scale erosion rates, may have increased sediment flux by an order of
magnitude during wetter periods on longer time scales in the past. Overall, these findings underscore (1)
the fundamental importance of climate-driven processes in the long-term landscape evolution of
tectonically active mountain belts; (2) the importance of climatic forcing on sediment production, mass
transfer, and permanent vs. transient sediment storage in orogens; and (3) the importance of climate
variability in intensifying erosion and sediment-flux rates on millennial time scales.
Modeling climate change effects on the hydrology of Pacific Northwest wetland ecosystems
Alan F Hamlet1, Se-Yeun Lee1, Maureen Ryan1
University of Washington, Seattle, WA, United States.
1
Climate change is arguably the greatest conservation challenge ever encountered by the ecological
management community. Local governments and land management agencies are being asked to
systematically assess vulnerability of diverse wetlands habitats to climate change impacts, and to develop
sustainable adaptation strategies to mitigate projected impacts. These activities are generally hindered by
lack of appropriate information and data resources for decision-making. We developed hydrologic
projections of climate change impacts on wetlands in the Pacific Northwest (PNW) to help develop
targeted climate adaptation strategies for a broad range of species reliant on wetland habitats. Using
1/16th degree soil moisture simulations from the Variable Infiltration Capacity (VIC) for three soil layers
and correlation analysis, we identified which soil layers are the best predictors of wetland response for a
range of different wetland sites and types. We then fit regression equations between the best predictors of
wetland response and observed wetland volume or water depth. These simple empirical models reproduce
historical wetland response at a number of different sites Mt. Rainier, WA and Trinity Alps Wilderness,
CA for the summer drawdown season quite well overall. Finally, we use these same regression models to
characterize wetland response to climate change. Simulations of future wetland response for wetland sites
on Mt. Rainier, for example, show that warmer and drier summers are likely to cause earlier drawdown, a
more rapid recession rate, and reduced water levels in summer. The results from the different case studies
are also analyzed to identify robust predictors of the calendar date of drying of ephemeral wetlands,
which can then be used to assess impacts over large geographic areas. These encouraging initial results
will be extended in future work to assess the performance of these kinds of tools over different ecoregions in the Pacific Northwest using data collected via improved field studies and remote sensing, and
will include estimates of water temperature as well.
Biogeochemical responses of two alpine lakes to climate change and atmospheric deposition, Jasper
and Banff National Parks, Canadian Rocky Mountains
William Hobbs1, 2, Rolf D Vinebrooke3, Alexander P Wolfe2
1
St. Croix Watershed Research Station, Science Museum of Minnesota, Marine on St. Croix, MN, United
States.
2
Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada.
3
Biological Sciences, University of Alberta, Edmonton, AB, Canada.
The sensitivity of remote alpine ecosystems to global change has been documented by 20th century
changes in climate, glacial recession, and terrestrial and aquatic ecosystems. In many cases the magnitude
and dominance of abiotic drivers on recent changes in alpine lakes is often mediated by processes within
the hydrologic catchment. Here we present sedimentary records of biogeochemical responses in two
alpine lake ecosystems to multiple environmental drivers over the last ~ 500 years in Banff and Jasper
National parks. We combine paleoecological measures of primary production (fossil microbial pigments)
and diatom community structure with geochemical proxies of reactive N (Nr) deposition to describe the
nature and rate of recent ecosystem changes. Curator Lake in Jasper shows a strong diatom response to
the limnological effects of climate warming (e.g. thermal stratification), but little evidence of changes in
Nr cycling over the last ~500 years. The response of McConnell Lake in Banff to climate change is
strongly mediated by glacial activity within the catchment, and changing inputs of Nr. Our findings
highlight the range of limnological responses that may be expressed by similar ecosystems subjected to
comparable abiotic stressors, while further documenting the magnitude of the ecological footprint
associated with recent environmental change in mountain park environments.
Coupled modeling of geomorphology and ecohydrology: Topographic feedbacks driven by solar
radiation
Erkan Istanbulluoglu1, Javier H Flores Cervantes1, Omer Yetemen1
1
Civil and Environmental Eng., Univ of Washington, Seattle, WA, United States.
There is a two-way coupling between geomorphic processes and vegetation dynamics. To examine the
role of vegetation on landform development, landscape evolution models (LEMs) have used relatively
simple theory of erosion-vegetation interactions and vegetation dynamics based on field evidence and
conjecture. Such modeling studies have described “with broad strokes” the control of vegetation on
landscape relief, drainage density, and sediment yields in a range of model sensitivity studies, often
without any direct field confirmation. For improved predictions of climate-landscape relations in realworld cases, and identify the need for future model development, there is strong need for field
confirmations of ecohydrologic LEMs. In this talk, we first discuss some of the key findings of recent
LEM studies that incorporate vegetation. Second, we introduce the role of solar radiation on
ecohydrologic processes in the CHILD LEM, and confirm model predictions against observations. Using
the model we examine how solar radiation control the spatio-temporal dynamics of soil moisture,
vegetation biomass, and their feedback on landform development in a semi-arid climate across a latitude
gradient. We identify that at the catchment scale while the initial greening usually takes places relatively
uniformly in space, the growing season takes longer on north facing slopes leading to higher overall
biomass on north aspects. Through eco-geomorphic feedbacks, this leads to steeper north facing slopes,
and increased valley asymmetry in the modeled landscapes. These findings are important to improve the
predictions of climate change impacts on the landscape system.
Precipitation intensity and vegetation controls on geomorphology of the central Andes
Mairi Louise Jeffery1, Christopher J Poulsen1, Todd A Ehlers2, 1, Brian J Yanites1
1
Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, United
States.
2
Department of Geosciences, Universität Tübingen, Tübingen, Germany.
Field observations and landscape evolution models indicate that landscape processes in active mountain
belts are strongly dependent on vegetation and climate. In fluvial landscapes, erosional efficiency is
commonly thought to depend on the intensity, frequency, and duration of precipitation events. We use
Tropical Rainfall Measuring Mission (TRMM) observations to test the importance of precipitation
intensity in determining geomorphology at the mountain belt scale. Precipitation metrics, including mean
annual precipitation, and the mean intensity, duration, and frequency of precipitation events, are derived
from the TRMM 3B42v7 product. The new precipitation datasets are then compared with different
topographic metrics of the central Andes. Statistical analyses, including multiple linear regression, are
used to quantify the importance of different precipitation metrics in controlling the regional topographic
characteristics. In addition to climate properties, spatial variations in tectonic regime, bedrock lithology,
and the amount and type of vegetation cover are accounted for in the statistical analyses.
Our analysis indicates that in regions with high vegetation cover (>80%), mean precipitation intensity and
mean interval correlate most strongly with mean hillslope (r = -0.51 and r = -0.66 respectively). In these
regions, mean hillslope decreases from ~25° to ~ 10° with increasing mean event precipitation intensity
(from 10 to 40 mm/day). In contrast, in sparsely vegetated (<40%) or shrub-dominated landscapes,
precipitation intensity does not correlate with mean hillslope (r < 0.1). In regions with high vegetation
cover, mean annual precipitation is weakly correlated with mean hillslope (r = 0.24). However, mean
hillslope increases with increasing mean annual precipitation (r = 0.52) when all vegetation cover is
considered.
We interpret the results as evidence that vegetation is a key control on critical erosion thresholds at the
landscape scale. Furthermore, the property of precipitation that governs surface processes is dependent on
the amount and type of vegetation cover. Both grass and trees effectively increase erosion thresholds and
act to stabilize the landscape. Only precipitation events that are capable of exceeding the erosion
threshold set by the vegetation can do geomorphic work. High mean slopes (15 - 33°) develop where the
mean precipitation intensity is low (<20 mm/day) and vegetation cover is high (>80%). In contrast,
regions that are dominated by shrubs or that have sparse vegetation cover have a lower erosion threshold,
and a greater proportion of precipitation events are effective erosion agents. Vegetation cover is also
dependent on climate but is more closely correlated with mean annual precipitation and mean event
duration than precipitation intensity. Precipitation controls on topography are therefore complex and
mediated by vegetation cover but are evident at a mountain belt scale.
What controls the long-term sediment flux from headwater catchments in the low mountain ranges
of central Europe?
Annegret Larsen1, 2, Hans-Rudolf Bork1, Tobias Heckmann4, Joshua Larsen3
1
Ecosystem Science, University of Kiel, Kiel, Germany.
2
University of Sydney, Sydney, NSW, Australia.
3
University of New South Wales, Sydney, NSW, Australia.
4
Universitaet Eichstaett-Ingolstadt, Eichstaett, Germany.
During the Medieval Period, agricultural expansion into steeper catchments of central Europe led to a
well documented increase in slope erosion. This in turn has been used to explain the apparent rapid
aggradation of downstream floodplains, as well as the possible conversion of river regimes from multithread to meandering. However, both a long term context in which to place this period of increased
erosion, and an appropriate quantification of the sediment fluxes, remain largely undetermined from these
headwater catchments. In order to address some of these knowledge gaps, we examined a small (42 ha)
headwater gully system in the Spessart mountains of central Germany. Detailed measurements and
chronology were obtained from all major sediment sources and sinks, including the slope catena, gully
thalweg, gully fan, and the floodplain of the adjacent trunk stream (Elsava River). Our results demonstrate
the ability of the gully thalweg to effectively store the bulk of eroded sediment derived from slope
instability during periods of diminished vegetation cover (Younger Dryas, Medieval Period). Interestingly,
sediment export does not occur in our catchment until slopes are re-stabilized by vegetation, as was the
case for most of the Holocene, and the last ~ 500 years, following recovery from Medieval deforestation.
This suggests that whichever forcing controls vegetation removal, climate (Younger Dryas), or humans
(Medieval Period), also determines slope erosion, but not the export of this sediment to downstream
floodplains. Likewise, the development of sufficient vegetation cover to reduce slope sediment supply is
the critical condition which determines the ability of the gully to incise, and export sediment to trunk
streams. In terms of the sediment budget, the recent (last ~500 years) release of silty sediment stored in
the gully thalweg (derived from Medival slope erosion) was 4.3 ± 0.32 kt. Compared to Holocene
sediment flux, whose cumulative export is not greater than the error range of the mass balance, the recent
activity represents the largest phase of sediment export in the last ~12 000 years. This also corresponds to
the only record of stratigraphic inter-connection between the gully fan and floodplain of the trunk stream,
which has also become silt dominated. This study provides a clear process understanding of the links
between the dominant controls on headwater catchment erosion, and downstream floodplain activity, and
has implications for how climate and human impacts are interpreted in the Holocene sedimentary records
of the mountain landscapes of central Europe.
Sharing the rivers: Balancing the needs of people and fish against the backdrop of heavy sediment
loads downstream from Mount Rainier, Washington
Christopher S Magirl1, Jonathan A Czuba1, Christiana R Czuba1, Christopher A Curran1
1
U.S. Geological Survey, Tacoma, WA, United States.
Despite heavy sediment loads, large winter floods, and floodplain development, the rivers draining Mount
Rainier, a 4,392-m glaciated stratovolcano within 85 km of sea level at Puget Sound, Washington, support
important populations of anadromous salmonids, including Chinook salmon and steelhead trout, both
listed as threatened under the Endangered Species Act. Aggressive river-management approaches of the
early 20th century, such as bank armoring and gravel dredging, are being replaced by more ecologically
sensitive approaches including setback levees. However, ongoing aggradation rates of up to 8 cm/yr in
lowland reaches present acute challenges for resource managers tasked with ensuring flood protection
without deleterious impacts to aquatic ecology. Using historical sediment-load data and a recent reservoir
survey of sediment accumulation, rivers draining Mount Rainer were found to carry total sediment yields
of 350 to 2,000 tonnes/km2/yr, notably larger than sediment yields of 50 to 200 tonnes/km2/yr typical for
other Cascade Range rivers. An estimated 70 to 94% of the total sediment load in lowland reaches
originates from the volcano. Looking toward the future, transport-capacity analyses and sedimenttransport modeling suggest that large increases in bedload and associated aggradation will result from
modest increases in rainfall and runoff that are predicted under future climate conditions. If large
sediment loads and associated aggradation continue, creative solutions and long-term management
strategies are required to protect people and structures in the floodplain downstream of Mount Rainier
while preserving aquatic ecosystems.
Northern rocky mountain wildfires and debris flows: Millennial-scale interactions among climate,
fire, vegetation, and geomorphic response
Jennifer L Pierce1, Kerry E Riley1, Kerrie Weppner1
1
Geosciences, Boise State University, Boise, ID, United States.
As summer droughts and rising temperatures in the Western U.S. continue to fuel large wildfires,
understanding the role of fire in mountain ecosystems becomes increasingly relevant. Past relationships
among fire, climate, and vegetation change may help place recent fires within a historic context. In
addition, post-fire floods and debris flows contribute large amounts of sediment to rivers and streams.
Quantifying fire-related sediment inputs is important for disciplines ranging from stream ecology to
landscape evolution.
We examine evidence of fires and related hillslope erosion through 14C dating of alluvial charcoal
fragments preserved in Holocene fire-related deposits in alluvial fans and stream sediments throughout a
range of ecosystems in Idaho, USA. In addition, we measure sediment yields from recent fire-related
debris flows and extrapolate the contribution of fire-related sediment inputs to streams over millennial
timescales.
Over Holocene timescales, independent records of forest-fires and fire-related erosion from ecosystems
ranging from sagebrush steppe, pinion-juniper, ponderosa pine, lodgepole pine and mixed conifer forests
indicate that sedimentation rates and processes on alluvial fans vary temporally with Holocene climate,
and spatially with vegetation type. Despite variations in ecosystem type and associated fire regimes, many
sites show similar broad-scale patterns. During the Pleistocene-Holocene transition large fires burned
across many ecosystems. The mid-Holocene (~4-8 ka) is characterized by few fire-related deposits;
however, this relatively fire-free interval is punctuated by fire peaks and associated sheetflooding ~7-6 ka.
Since regional paleoclimatic reconstructions indicate the mid-Holocene was generally warm and dry the
lack of fire is somewhat counterintuitive; however, decreased fuel loads, combined with perhaps a more
stable climate may reduce fire and storm intensity and frequency. The late Holocene (last ~3 ka) cooler,
wetter and more variable climates are characterized by an increase in fire activity at all sites, and a
general increase in large debris flows. Medieval droughts correspond with major fire and debris flow
peaks ~1000-800 cal yr BP; decadal to annual droughts during the generally cooler and wetter LIA also
promote fire peaks ~500-300 cal yr BP. The last ~ 3 ka also corresponds with the arrival of fire-prone
pine species at several of the study areas.
In the Middle Fork Salmon River of central Idaho, > 40% of the watershed has burned in the last 30 years
and erosion from severely burned hillslopes produced many large fire-related debris flows. Fire-related
deposits compose 74 ± 25% of total alluvial fan thickness in upper wetter ecosystems versus 41 ± 33%
recorded in lower drier basins. Recent (1997-2008) moderate to high-severity fires produced debris flows
in tributary basins underlain by easily erodible Idaho Batholith granites. Sediment yields from these
debris flow range from ~1,450-34,550 Mg/km2. Over the last 6 ka, we estimate fire-related debris flows
have contributed ~30-100 Mg/km2/ yr of sediment to the Middle Fork Salmon River.
POSTERS
Session title: Climate Change in Mountain Environments
New measurements of particulates in glacial snow and ice in the Cordillera Blanca Mountains of
Peru
John All1, Carl Schmitt2, Aaron J Celestian1, Melinda Rucks1, William P Arnott3, Rebecca Cole4
Western Kentucky University, Bowling Green, KY, United States.
2
NCAR, Boulder , CO, United States.
3
University of Nevada, Reno , NV, United States.
4
INSTAAR, Boulder , CO, United States.
1
During the local dry season (June/July) of 2011 and 2012, the American Climber Science Program
(organized with the assistance of the American Alpine Club) conducted scientific expeditions in
Huascaran National Park in Peru. The Park is located in the Cordillera Blanca mountain range and
contains the world’s largest collection of tropical mountain glaciers. One component of the environmental
research program was sampling particulates on glacier surfaces by means of snow collection and filtration.
Over 150 samples were collected during the two expeditions by volunteer climbers working with
scientists in the field. Glacier snows were collected on over fifteen peaks throughout the range at altitudes
from 4800 to nearly 6800 meters. Snow samples were kept frozen until the climber-scientists returned to
basecamp - at which point they were rapidly melted and then immediately filtered through 0.7 micron
PallFlex tissuequartz filters. The particulates captured on the filters have been analyzed for their bulk heat
absorption properties as well as to determine the properties of individual particles through X-ray
diffraction for bulk mineral identification, and Raman microscopy for chemical mapping of minerals.
Preliminary results indicate that snow age, altitude, as well as geographic location (with respect to urban
areas, mines, and predominant wind direction) all play significant roles in the amount and types of
contaminants. Multiple locations were sampled during both expeditions as well as at different times
during the same climbing season. Results include the relative heating capacity of the samples at various
wavelengths as well as mineral composition information across the range. Local weather patterns and
geographic observations will be used to identify potential sources of contaminants. Sampling will
continue under the American Climber Science Program in 2013 and beyond.
Elevation, substrate, & climate effects on alpine & sub-alpine plant distribution in California’s high
mountains: preliminary data from the California GLORIA Project
Adelia Barber1, Constance I Millar2, Jim Bishop4, Catie Ann Bishop4, Christopher Kopp3, Ann Dennis4
Dept. of Ecology & Evolutionary Biology, Univ. of California Santa Cruz, Santa Cruz, CA, United
States.
2
Pacific SW Research Station, USDA Forest Service, Albany, CA, United States.
3
Section of Ecology, Behavior & Evolution, Univ. of California, San Diego, San Diego, CA, United
States.
4
California Section, Global Observation Research Initiative in Alpine Environments (GLORIA), Oroville,
CA, United States.
1
Plant distribution varies with elevation, substrate, and climate. Documenting plant response to global
climate change, in sensitive zones such as the alpine, is a major goal for global change biology.
Understanding how plant communities reflect elevation and substrate is critical to analyzing plant
response to climate change on regional scales. In California’s alpine zone, community composition can
change over as little as 25 meters in elevation, and multiple substrates are found in close proximity. Basic
information on alpine plant distribution by elevation and substrate provides a basis for anticipating which
species may be reduced with a warming climate, which likely to persist, and which could replace those
that decline.
The Global Observation Research Initiative in Alpine Environments (GLORIA) is a worldwide effort to
document vegetation changes over time in alpine settings using permanent multi-summit plots.
Established in North America in 2004, we currently monitor six permanent GLORIA target regions,
composed of 21 high summits in California’s alpine and subalpine zone. High resolution plant occurrence
and cover data from the upper 10 meters of each summit is presented, from 4325 meters in elevation to
3250 meters. The summits span the ranges of eastern-central California, ranging in substrate from
dolomite to granite, to argillized acidic volcanics. Additionally, plant frequency and cover are assessed at
25 meter elevation intervals, with 100-meter belt transects on contour, overlapping profiles, extending
downward from four summits in the White Mountains.
Species richness varies 10X over our 1000-meter elevation range. Plants from our data can be generally
divided into 3 groups: 1. Summit specialists (ex: Polemonium chartaceum) only on top of the highest
peaks, 2. Alpine plants (ex: Phlox condensata and Astragalus kentrophyta) predominantly within the
alpine zone but sometimes into the upper sub-alpine zone, and 3. Broadly distributed plants (Elymus
elymoides and Chrysothamnus viscidiflorus) from the alpine zone to the valleys. Rock substrate and
microsite soil development have a strong effect on plant community composition and species richness (ex.
volcanic rocks were found to support 2x more species than dolomite).
Impacts of climate change on plant communities will be assessed by repeating the GLORIA protocol
every 5 years and recording soil temperature on all four aspects at each summit. We present the first set of
5-year resurvey and temperature data from 18 summits and 4 down-slope belt transects. We have
documented considerable annual variation in species presence/absence at almost all sites. Consistent with
the expectation of rising global temperatures, our soil temperature loggers have documented a rise of 1degree Celsius at most of our sites. This data (2004 through 2012 for different sites) is a baseline dataset
for assessing bioclimatic shifts and future plant composition in California's alpine zone.
Modeling the impact of climate warming on the range of brook trout in the Blue Ridge Mountains,
USA
Marshall G Bartlett1
1
Physics, Hollins University, Roanoke, VA, United States.
Brook trout in the Eastern United States (Salvelinus fontinalis) thrive in a relatively narrow range of
stream temperatures. Over the past several centuries, the introduction of competitive species has pushed
brook trout to the cooler, upstream margins of what use to be a much more extensive range within most
drainages. Over the next several decades, climate change may put further thermal pressure on the species,
increasing the fragmentation of their distribution and shrinking their present range. Because the size and
connectivity of habitats seem to influence the persistence of local populations, climate warming leading to
increased fragmentation of remaining habitats could accelerated species decline. Using the Regional
Hydrological and Ecological Simulation System (RHYSSys), I modeled the projected habitat changes for
a group of native brook trout streams in the Blue Ridge Mountains of South-Central Virginia, USA. The
modeling process is illustrative of the need for better understanding of the couplings that exist between
geomorphology, hydrology, and ecology, particularly in mountain environments. Model results are
quantified according to the degree of decrease in stream-miles of habitat and the increase in the
fragmentation of the habitat as a function of the warming rate (degrees per decade). These results may
help inform habitat management strategies for the coming several decades in the region, and the modeling
process helps highlight the need for more refined understanding of climate change’s impacts on
habitability.
Quantifying thermal constraints on carbon and water fluxes in a mixed-conifer sky island
ecosystem
Zev Braun1, 2, Rebecca L. Minor2, Daniel L Potts3, Greg A. Barron-Gafford2
Biology, Grinnell College, Grinnell, IA, United States.
2
Biosphere 2, University of Arizona, Tucson, AZ, United States.
3
Biology, Buffalo State, Buffalo, NY, United States.
1
Western North American forests represent a potential, yet uncertain, sink for atmospheric carbon.
Revealing how predicted climatic conditions of warmer temperatures and longer inter-storm periods of
moisture stress might influence the carbon status of these forests requires a fuller understanding of plant
functional responses to abiotic stress. While data related to snow dominated montane ecosystems has
become more readily available to parameterize ecosystem function models, there is a paucity of data
available for Madrean sky island mixed-conifer forests, which receive about one third of their
precipitation from the North American Monsoon. Thus, we quantified ecophysiological responses to
moisture and temperature stress in a Madrean mixed-conifer forest near Tucson, Arizona, within the
footprint of the Mt. Bigelow Eddy Covariance Tower. In measuring a series of key parameters indicative
of carbon and water fluxes within the dominant species across pre-monsoon and monsoon conditions, we
were able to develop a broader understanding of what abiotic drivers are most restrictive to plant
performance in this ecosystem. Within Pinus ponderosa (Ponderosa Pine), Pseudotsuga menziesii
(Douglas Fir), and Pinus strobiformis (Southwestern White Pine) we quantified: (i) the optimal
temperature (Topt) for maximum photosynthesis (Amax), (ii) the range of temperatures over which
photosynthesis was at least 50% of Amax (Ω50), and (iii) each conifer’s water use efficiency (WUE) to
relate to the balance between carbon uptake and water loss in this high elevation semiarid ecosystem. Our
findings support the prediction that photosynthesis decreases under high temperatures (>30°C) among the
three species we measured, regardless of soil moisture status. However, monsoon moisture reduced
sensitivity to temperature extremes and fluctuations (Ω50), which substantially magnified total
photosynthetic productivity. In particular, wet conditions enhanced Amax the most dramatically for P.
menziesii, elevating rates by 590%, while Ω50 grew most substantially for P. strobifomis (by 180%).
Interspecific differences in temperature optima (Topt) elucidated possible species dominance predictions
for seasonal and gradual temperature changes. P. menziesii may out-perform the pine species in the event
that temperatures rise in conjunction with abundant summer moisture. However, if monsoon rains fail to
accumulate, P. menziesii may remain at subsistence levels of photosynthesis. Together, these data will
enable the parameterization of models to approximate the productivity and, ultimately, the composition of
Madrean sky island mixe d-conifer forests under forecasted climate conditions of increased temperatures
and more frequent drought.
A GIS based geomorphic assessment to quantify spatially distributed groundwater recharge in
mountain watersheds
Devin William Cairns1, James M Byrne1, Daniel L. Johnson1
University of Lethbridge , Lethbridge, AB, Canada.
1
Groundwater recharge and flow originating in mountain watersheds is difficult to quantify due to
challenges in data collection to characterize the local geology. Groundwater subroutines should be
included in more hydrological models, as groundwater controls many aspects of water quantity and
quality. We propose a method for developing a spatially distributed groundwater recharge model for
mountain environments. This work will utilize available digital elevation models and satellite imagery to
complete surface analyses of the watershed. The surface analyses will be used to estimate the local
hydrogeology based on the geomorphic properties throughout the watershed. Spatially distributed
groundwater flow-related variables will be estimated to simulate the rate of groundwater recharge over
time based on inputs from the hydrometeorological model.
Large-scale simulation of the effects of climate change on runoff erosion following extreme wildfire
events
Gregory Gould1, Jennifer C Adam1, Michael E Barber1, Joe W. Wagenbrenner2, Peter R Robichaud2, Lili
Wang3, Keith Aric Cherkauer3
1
Washington State University, Pullman, WA, United States.
2
USFS, Moscow, ID, United States.
3
Purdue University, Purdue, IN, United States.
Across the western U.S., there is clear concern for increases in wildfire occurrence, severity, and post-fire
runoff erosion due to projected climate changes. The aim of this study was to advance our capability to
simulate post-fire runoff erosion at scales larger than a single hillslope to examine the relative
contribution of sediment being released to larger streams and rivers in response to wildfire. We applied
the Variable Capacity Infiltration-Water Erosion Prediction Project (VIC-WEPP), a newly-developed
physically-based modeling framework that combines large-scale hydrology with hillslope-scale runoff
erosion, over the Salmon River basin (SRB) in central Idaho. We selected the SRB for this study because
of recent research that suggested that forest wildfires are likely contributing the majority of coarser sands
that settle in downstream navigation channels and in reservoirs, causing adverse impacts to aquatic life,
navigation, and flood storage. Using the Normalized Burn Ratio (NBR), burn intensity and severity maps
show the regularity of wildfire occurrence in the SRB. These maps compare pre-fire images to next
growing season images from the Landsat Thematic Mapper multispectral scanning sensor. Rather than
implementing WEPP over all hillslopes within the SRB, we applied a representative hillslope approach. A
monofractal scaling method downscales globally available 30 arc second digital elevation model (DEM)
data to a 30 m resolution for simulations. This information determined the distribution of slope gradients
within each VIC grid cell. This study applied VIC-WEPP over the 1979-2010 period and compared an
ensemble of future climate simulations for the period of 2041-2070. For future scenarios, we only
considered meteorological impacts on post-fire erosion and did not incorporate changes in future fire
occurrence or severity. We ran scenarios for a variety of land cover and soil parameter sets, particularly
those that relate to pre and post-fire characteristics, such as vegetative cover, interrill and rill erodibility
factors, and saturated hydraulic conductivity. Evaluation of runoff erosion at experimental sites, observed
by the U.S. Forest Service, involved using Disturbed WEPP which showed reasonable first post-fire year
annual erosion predictions. We evaluated VIC-WEPP by comparing sediment observations downstream
of the SRB with simulated yields for both pre and post-fire conditions. Generation of maps showing
erosion over the SRB for each of the scenarios show specific areas within the SRB to be high, moderate,
or low runoff-induced post-fire erosion regions. Our methodology will enable forest managers in the
region to incorporate the impacts of changes in meteorological events on runoff erosion into their
strategic management plans.
Diatom community changes in five sub-alpine mountain lakes in northern California
Briana Johnson1, Paula J. Noble1, Kerry Howard1, Alan Heyvaert2
1
Department of Geological Sciences & Engineering, University of Nevada, Reno, Reno, NV, United
States.
2
Division of Hydrologic Sciences, Desert Research Institute, Reno, NV, United States.
Sediment cores and/or phytoplankton sampling of five sub-alpine lakes within three northern California
mountain ranges show a major shift in diatom phytoplankton communities over the past 20-60 years;
however, specific causes of these changes are still under investigation. Diatom analysis of a 20-cm
sediment core taken from Castle Lake, a meso-oligotrophic lake located on the eastern slope of the
Klammath Mountains, shows the phytoplankton community shifted from being cyclotelloid-dominated to
having a larger component of araphids beginning around 1997. In the lower 14 cm of the core, the
phytoplankton are dominated by centric diatoms, including the Discostella stelligera-pseudostelligera
group (>50% of total diatoms), and the Cyclotella occelata-rossii-tripartita complex (9-18%). The top 6
cm show an increasing shift towards araphids, including Asterionella formosa and the Fragilaria tenerananana group, which is consistent with phytoplankton in the lake’s epilimnion today. Fallen Leaf Lake
(FLL), located at the southern end of the Lake Tahoe basin, has also undergone a similar shift. Presently,
A. formosa, the F. tenera-nananna group, and Tabellaria dominate the phytoplankton. Examination of a
sediment core from FLL indicates that A. formosa has been present in high abundances since at least 1812.
The most prominent shift in the FLL diatom population began in the 1950s when the centric diatoms (eg.
Aulacoseira subarctica) declined significantly in favor of araphids. The F. tenera-nanana group was
present in trace amounts before 1812 and dramatically increased in abundance after the 1950s. Sediment
accumulation rates have increased steadily since 1950 and coincide with increases in lake development
and recreational use. A. formosa is also present today in Gilmore Lake, a minimally human-impacted lake
located in the watershed above FLL, and in the heavily impacted Manzanita Lake in the northwestern
corner of Lassen Volcanic National Park (LAVO) at the southern end of the Cascade Range. Of the 16
LAVO lakes surveyed, Manzanita Lake was the only lake dominated by A. formosa during the spring
bloom. Widow Lake, a remote lake less impacted by humans in the northeastern corner of LAVO was
dominated by the F. tenera-nanana group. Recent shifts to an A. formosa-dominated diatom community
have been attributed to atmospheric nitrogen (N) deposition in remote sub-alpine lakes in western North
America and Canada. The dominance of A. formosa in these N. California lakes may indicate a similar
phenomenon; however, at least in the FLL watershed, water quality data suggests that spring pulses of N
appear to be related to flushing of the upper watershed, not wet N deposition in snowpack. Furthermore,
the A. formosa shift in FLL predates the phenomenon elsewhere, and the F. tenera-nanana shift in FLL
that began 60 years ago coincides best to increases in lake development and recreation. Likewise, in
LAVO, the lake with the highest recreational impact shows the greatest abundance of A. formosa.
Presently, no unifying cause can be pinpointed to explain the increase of A. formosa in the N. California
lakes sampled. Other factors besides atmospheric nitrogen deposition will need to be explored to explain
the recent increases of A. formosa and the F. tenera-nanana group, including changes in land use
throughout the watersheds, fish manipulations, and climate variability.
Effects of climate change on hydrology and water management in the Skagit River Basin
Se-Yeun Lee1, Alan F Hamlet1
Civil and Environmental Engr., University of Washington, Seattle, WA, United States.
1
Based on global climate model (GCM) scenarios from the Intergovernmental Panel on Climate Change
Fourth Assessment Report (IPCC AR4) and subsequent hydrologic modeling studies for the Pacific
Northwest, the impacts of climate change on hydrology in the Skagit River Basin are likely to be
substantial under natural (unregulated) conditions. To assess the combined effects of increasing extreme
flows (floods and low flows) and dam operations that determine impacts to regulated flow, a new
integrated daily time step reservoir operations model was built for the Skagit River Basin. The model
simulates current reservoir operating policies for historical flow conditions and for projected flows for the
2040s and 2080s using five different GCMs with the A1B emissions scenarios, and estimates sediment
loading. By simulating alternative reservoir operating policies that provide increased flood storage and
start flood evacuation one month earlier, prospects for adaptation in response to increased flood risks are
considered. Results from the daily time step reservoir operations modeling show that regulated hydrologic
extremes in the basin will likely become more intense. The regulated 100-year flood is projected to
increase substantially in the future in comparison with historical regulated 100-year flood (23% by the
2040s and 40% by the 2080s). The regulated extreme 7-day low flows (7Q10) are also projected to
decrease by about 30 % in the future. Alternative flood control operations (earlier and larger drafting of
reservoirs) are shown to be largely ineffective in mitigating the increased flood risks in the lower Skagit,
supporting the argument that climate change adaptation efforts will need to focus primarily on improving
management of the floodplain, rather than focusing on modifying flood control operations in existing
headwater projects. Projected changes in the Skagit River’s flow regime are shown to have dramatic
effects on estimated total suspended sediment load in the basin. Peak winter (DJF) sediment loadings
increased by a factor of 3.7 on average, and mean annual loadings increased from 2.4 to 5.8 million
metric tons per year by the 2080s. These changing sediment regimes have important management
implications for the Skagit floodplain and delta, and for Puget Sound.
Seasonal accumulation and depletion of localized sediment stores of four headwater catchments in
the Sierra Nevada Mountains, California.
Sarah Elizabeth Martin1, Martha H Conklin1, Roger C Bales1
University of California, Merced, Merced, CA, United States.
1
Seasonal turbidity patterns and event-level hysteresis analysis of turbidity verses discharge in four 1 km2
headwater catchments indicate localized in-channel sediment sources and a seasonal accumulationdepletion pattern of stream sediments. Our hypothesis is that during low-flow periods, sediment
accumulates at the toe of banks and is entrained and transported downstream during high-flow events,
with successive storm events depleting sediment stores. Turbidity signals were analyzed during fall rain
events, early to mid-winter snow-melt events, spring snow-melt, and summer dry periods. Two
catchments in the American River basin at approximately 1580 m elevation and two catchments in the
Merced River basin at approximately 1760 meters elevation were used in this study. All study catchments
are characterized by a Mediterranean climate with a distinct wet and dry season and are in the rain-snow
transition zone, with snow making up roughly 40 to 60 percent of average annual precipitation. Turbidity
events tend to be infrequent and of short duration in these basins. Seasonal patterns within the four
catchments include more turbidity events associated with fall rainstorms and early to mid- winter melt
events than associated with peak snow-melt. When multiple discharge events occurred in succession, the
largest turbidity spike was often associated with the first event and not necessarily associated with the
largest discharge event. This pattern is indicative of a seasonal depletion of localized sediment stores,
with the majority of accumulated sediment being transported in the first storm, leaving less available for
subsequent events. Turbidity spikes were also seen during base-flow periods when no discharge events
were occurring, likely from the buildup of organic matter rather than the movement of mineral-based
materials. An examination of hysteresis loops for individual storm events showed that a clockwise pattern,
where turbidity peaks before discharge, was dominant suggesting a localized sediment source. In
successive storm events, hysteresis loops shifted from a clockwise pattern to a more random pattern, with
turbidity and discharge peaking concurrently. This delay in the turbidity peak suggests that sufficient flow
energy must be reached to start entraining the more consolidated bank/bed sediment or that the dominant
sediment sources may be shifting to less localized areas such as hill slopes. Both of these scenarios
support our hypothesis of seasonal accumulation and depletion of local sediment stores.
Thermal and hydrologic attributes of rock glaciers and periglacial talus landforms; Sierra Nevada,
California, USA
Constance I Millar1, Robert D Westfall1, Diane L Delany1
1
PSW Research Station, USDA Forest Service, Albany, CA, United States.
To explore thermal regimes and hydrologic capacity of rock glaciers and related periglacial talus
landforms, we deployed mini-thermochrons in and around potentially ice-embedded features of the Sierra
Nevada. Results from studies at 13 rock glaciers and 8 taluses indicate that outlet springs from these
landforms generally do not desiccate but persist year-round as ice (frozen) in winter and flowing water in
the warm season. Temperatures of water (liquid and ice) in rock-glacier outlet springs had an annual
mean of -0.2°C and mean of 0.6°C during the warm season with very low diurnal fluctuation. These and
other attributes suggest the existence of internal ice and/or permafrost supplying the springs. Air
temperatures of rock-glacier matrices (1 m below the surface) versus surface air corroborate the
periglacial nature of internal environments: annual air temperatures of matrices were below freezing
(mean, -0.8°C). Compared to surface air, especially during the warm season, matrix air temperatures were
significantly colder and fluctuated less. Talus landforms followed a similar pattern, although water- and
matrix air temperatures were warmer, and contrasts with surface air were not as strong as for rock glaciers.
For rock glaciers and talus slopes, matrix air temperatures showed resistance (buffering) to changes in
external air temperatures. Unique geomorphic conditions of rock glaciers and periglacial taluses in the
Sierra Nevada appear to maintain cool-buffered thermal regimes at least partly decoupled from external
air. Springs support persistent wetlands and lakes at their snouts, retaining water in otherwise semi-arid
high cirques, and contribute as hydrologic reserves and critical habitat for alpine biota. Daily and seasonal
lags and buffering effects suggest that ice within these landforms might resist surface warming on the
longer term, which could make these landforms increasingly important as regional climates change.
Physiological stresses of limber pine seedlings at and above treeline immediately following natural
and experimentally advanced snowmelt
Andrew B. Moyes1, Matthew J Germino3, Lara M Kueppers1, 2
UC Merced, Merced, CA, United States.
2
Lawrence Berkeley National Laboratory , Berkeley, CA, United States.
3
US Geological Survey, Boise, ID, United States.
1
Treeline positions are anticipated to shift uphill in response to climate warming, a prediction which
depends on future seedling recruitment at and above the current distribution limits of subalpine trees. To
examine the role of cold temperature in seedling establishment at treeline, we measured physiological
performance of limber pine seedlings after surviving their first winter in heated and ambient temperature
plots within the Alpine Treeline Warming Experiment. Fluorometric measurements of maximum
photosystem II efficiency (Fv/Fm) indicated severe photoinhibition 10 days following melt (Fv/Fm near
0), but photoinhibition diminished over the subsequent 10 days. Over the same period, seedlings showed
highly variable degrees of moisture stress in midday stem water potentials (Ψ), possibly related to frost
drought and freeze-thaw embolism, despite consistently abundant afternoon soil moisture. Many
seedlings would not exude water under maximum measurement pressure (Ψ < -5 MPa) across all
sampling dates (up to 60 days following melt), indicating high spatial variability in cold-associated
moisture stress, and possibly limited xylem conduit refilling. Net CO2 assimilation appeared to be
independently limited by photoinhibition and moisture stress. Although these stresses were not
significantly impacted by the timing of snowmelt or whether seeds were sourced from high or low
elevation provenances, the observation of severe cold stress indicates that seedling establishment above
treeline will be sensitive to future patterns of snowmelt and air temperature.
Using sensitive montane amphibian species as indicators of hydroclimatic change in meadow
ecosystems of the Sierra Nevada, California.
Ryan Peek1, Josh Viers1, Sarah M Yarnell1
1
Center for Watershed Sciences, UC Davis, Davis, CA, United States.
Climate change can affect sensitive species and ecosystems in many ways, yet sparse data and the
inability to apply various climate models at functional spatial scales often prevents relevant research from
being utilized in conservation management plans. Climate change has been linked to declines and
disturbances in a multitude of species and habitats, and in California, one of the greatest climatic concerns
is the predicted reduction in mountain snowpack and associated snowmelt. These decreases in natural
storage of water as snow in mountain regions can affect the timing and variability of critical snowmelt
runoff periods—important seasonal signals that species in montane ecosystems have evolved life history
strategies around—leading to greater intra-annual variability and diminished summer and fall stream
flows. Although many species distribution models exist, few provide ways to integrate continually
updated and revised Global Climate Models (GCMs), hydrologic data unique to a watershed, and
ecological responses that can be incorporated into conservation strategies. This study documents a novel
and applicable method of combining boosted regression tree (BRT) modeling and species distributions
with hydroclimatic data as a potential management tool for conservation. Boosted regression trees are
suitable for ecological distribution modeling because they can reduce both bias and variance, as well as
handle sharp discontinuities common in sparsely sampled species or large study areas. This approach was
used to quantify the effects of hydroclimatic changes on the distribution of key riparian-associated
amphibian species in montane meadow habitats in the Sierra Nevada at the sub-watershed level.
Based on modeling using current species range maps in conjunction with three climate scenarios (near,
mid, and far), extreme range contractions were observed for all sensitive species (southern long-toed
salamander, mountain yellow-legged frog, Yosemite toad) by the year 2100. Among many environmental
and hydroclimatic variables used in the model, snowpack and snowmelt (runoff) variables were
consistently among the most informative in predicting species occupancy. Few sub-watersheds contained
greater than 50% probability of species occupancy throughout the modeled time period; however several
core areas were identified as more resilient to climate change for each species. There was overlap among
species in areas that were predicted to remain hydroclimatically stable, particularly in sub-watersheds that
contain high meadow density. Quantifying these areas of habitat stability, or “resiliency”, may ultimately
be the most useful outcome of BRT modeling, with the flexibility to utilize multiple GCMs at varying
scales. Ultimately managers need to consider both short term and long term conservation goals by
identifying and protecting suitable habitat areas most resilient to climate change to give multiple species
the best chance to persist. This approach provides a unique tool for conservation management which can
be easily applied to a variety of data and species, and provides useful knowledge at both near and long
term time scales.
The influence of surface characteristics on lapse rates and temperature profiles in areas of complex
terrain
Nicholas C Pepin1, Gary Pike1, Daniel Fower1, Martin Schaefer1
Dept Geography Buckingham Bldg, Univ Portsmouth, Portsmouth, United Kingdom.
1
Temperatures near the ground are often decoupled from free-air equivalents, particularly in areas of
complex relief and at high latitudes where cold air drainage occurs particularly when radiation balances
become negative. This means that it is hard to predict spatial patterns of surface temperature in such
regions. In this study several years of intensive field measurements in complex terrain in northern Finland
(Kevo) and Sweden (Abisko) allow detailed examination of the interaction between land surface
characteristics (including cryosphere), vegetation, and local/micro-climate in mountain basins.
Temperature and vapour pressure were measured every 30 minutes for 5 years (2007-2012) at 60 sites at
Kevo and for a winter season (September-June) at 52 sites in Abisko, ranging over 300/600 metres of
elevation respectively. In Finland lapse rates vary considerably both seasonally and diurnally, the relative
importance of seasonal and diurnal forcing changing throughout the year. The results show intense (up to
+80 °C/km) and persistent inversion events during the winter months (NDJ) which are broken up by
mechanical effects since there is no diurnal cycle. In the transition from winter into spring (FMA) these
inversions still occur but increasing radiation imposes a diurnal pattern on their formation and destruction.
As snow cover peaks in spring the interaction between surface albedo, land cover and radiation serves to
amplify the diurnal cycle in lapse rates. Daytime lapse rates peak in spring because of an increase in
albedo with elevation as dark trees give way to reflective snow. At night inversions rapidly reform.
Summer lapse rates are modified (usually weakened) by the presence of open water at low elevations. In
Abisko similar processes are shown to be at work, although since the valley system is more open and at a
larger spatial scale, the range of lapse rate variability is slightly less and the influence of surface
characteristics more subdued.
Taken together these results suggest that expected land cover (reduced snow season, later freeze-up and
earlier melt) and synoptic changes (stronger westerly storm track) due to regional warming in the Arctic
will act to decrease the frequency and intensity of inversion formation, steepening mean lapse rates and
therefore increasing the relative amount of warming in valley floor locations above regional mean
warming.
Species-specific and seasonal differences in chlorophyll fluorescence and photosynthetic light
response among three evergreen species in a Madrean sky island mixed conifer forest
Daniel L Potts1, Rebecca L. Minor2, Zev Braun2, 3, Greg A. Barron-Gafford2
1
Biology, Buffalo State College, Buffalo, NY, United States.
2
B2 Earthscience, Biosphere 2, University of Arizona, Tucson, AZ, United States.
3
Grinnell College, Grinnell, IA, United States.
Unlike the snowmelt-dominated hydroclimate of more northern mountainous regions, the hydroclimate of
the Madrean sky islands is characterized by snowmelt and convective storms associated with the North
American Monsoon. These mid-summer storms trigger biological activity and are important drivers of
primary productivity. For example, at the highest elevations where mixed conifer forests occur, ecosystem
carbon balance is influenced by monsoon rains. Whereas these storms’ significance is increasingly
recognized at the ecosystem scale, species-specific physiological responses to the monsoon are poorly
known. Prior to and following monsoon onset, we measured pre-dawn and light-adapted chlorophyll
fluorescence as well as photosynthetic light response in southwestern white pine (Pinus strobiformis),
ponderosa pine (Pinus ponderosa), and Douglas fir (Pseudotsuga menziesii) in a Madrean sky island
mixed conifer forest near Tucson, Arizona. Photochemical quenching (qp), an indicator of the proportion
of open PSII reaction centers, was greatest in P. strobiformis and least in P. menziesii and increased in
response to monsoon rains (repeated-measures ANOVA; species, F2,14 = 6.17, P = 0.012; time, F2,14= 8.17,
P = 0.013). In contrast, non-photochemical quenching (qN), an indicator of heat dissipation ability, was
greatest in P. ponderosa and least in P. menziesii, but was not influenced by monsoon onset (repeatedmeasures ANOVA; species, F2,12 = 4.18, P = 0.042). Estimated from leaf area-adjusted photosynthetic
light response curves, maximum photosynthetic rate (Amax) was greatest in P. ponderosa and least in P.
menziesii (repeated-measures ANOVA; species, F2,8= 40.8, P = 0.001). Surprisingly, while the monsoon
positively influenced Amax among P. ponderosa and P. strobiformis, Amax of P. menziesii declined with
monsoon onset (repeated-measures ANOVA; species x time, F2,8 = 13.8, P = 0.002). Calculated as the
initial slope of the photosynthetic light response curve, light-use efficiency (AQE) was similar among P.
strobiformis and P. ponderosa and least in P. menziesii (repeated-measures ANOVA; species, F2,8 = 13.83,
P = 0.002). Across all three species, monsoon onset increased AQE (repeated-measures ANOVA; time,
F1,8= 10.04, P = 0.01). Likewise, P. strobiformis and P. ponderosa shared a similar, greater light
compensation point than P. menziesii (repeated-measures ANOVA; species, F2,8 = 5.89, P = 0.02).
However, across species, monsoon onset did not influence light compensation points. These results
support the hypothesis that the monsoon has species-specific effects on evergreen physiological
performance and are broadly consistent with predictions of stress tolerance based on species' latitudinal
and elevational range distributions. Moreover, with year-to-year rainfall variability predicted to increase
under future climate scenarios, species-specific functional traits related to stress tolerance and
photosynthesis may promote ecosystem functional resilience in Madrean sky island mixed conifer forests.
Stochastic analysis of multi-year runoff, recharge, and climatic water deficit in geologically varying
watersheds
Stuart B Weiss1, Alan L Flint2, Lorraine E Flint2
Creekside Center for Earth Observation, Menlo Park, CA, United States.
2
California Water Science Center, Sacramento, CA, United States.
1
Numerous climate futures are now available from downscaled global climate models. The translation of
monthly precipitation and temperatures into hydrologically and ecologically meaningful outputs for
managers and planners is the next frontier. The Basin Characterization Model (BCM) is used to generate
time series of annual runoff, recharge, and climatic water deficit (CWD) at the scale of small planning
watersheds in the San Francisco Bay Area. These watersheds differ in climate, soils, bedrock permeability,
and human use. We examine the occurrence of droughts in historical and projected climate records, and
develop metrics based on multi-year running averages. Projected droughts are compared with historical
droughts (1976-77, 1987-1992, and 2007-2009), providing analogs and benchmarks within recent
experience. Bedrock permeability affects runoff to recharge ratios, and soils produce fine-scale variability
in storage. Rising temperatures and potential evapotranspiration drive higher CWD even when average
annual precipitation increases, leading to greater stress on terrestrial and aquatic ecosystems. Quantifying
probabilities of drought stress by using time series analysis, extreme value statistics, and stochastic
simulation defines risks at fine spatial scales relevant to water and land managers, and can be
incorporated into existing water supply and flood management frameworks.
Assessment of the impacts of dynamic soil properties and vegetation cover on soil erosion using
distributed hydrological model
Tan Zi1, Gerard Kiely2, John D Albertson1
Civil and Environmental Engineering, Duke University, Durham, NC, United States.
2
Civil and Environmental Engineering, University College Cork, Cork, Ireland.
1
The challenges in soil erosion modeling are mainly attributed to the heterogeneity of the soil properties
and the complex interactions between vegetation cover and soil erosion processes. Current process-based
soil erosion models apply empirical adjustment factors to account for the influences of vegetation cover
and land managements. Most of soil erosion models assume that the temporal changes of soil properties
are negligible over temporal scale ranging from several days to decades. Physically meaningful model
representations of soil erosion processes require deep understanding of the mechanisms through which
vegetation cover influences the soil particles detachment and transport, as well as the temporal-spatial
changes of soil properties.
In this study, the dynamic changes of soil properties in soil erosion modeling were investigated, through a
distributed soil erosion model (GEOTOP-erosion). Specifically, spatially distributed and dynamical soil
variables are introduced into the soil erosion model. Soil particles associated with different grain sizes
experience different transport processes. Soil textures and organic matter (OM) contents are updated daily
according to the feedbacks on erosion and deposition processes. Other related soil properties are derived
by the updated soil textures and OM contents. The influences of vegetation cover are represented by four
major mechanisms: (1) modifying net rainfall and raindrop energy by canopy interception, (2) reducing
runoff generation by transpiration, (3) retarding overland flow by increasing surface roughness, and (4)
increasing soil cohesion by root system.
The simulations of this soil erosion model show appropriate interactions between vegetation cover and
soil erosion processes. The erosion process could also be dynamically adjusted by the evolution of soil
properties.
An experimental catchment in Ireland was selected to test the soil erosion model. The simulation results
show a good agreement between estimated and observed soil loss in complex land surface conditions. The
simulations incorporated dynamic soil properties demonstrate more accurate soil erosion simulation. The
coupled model could be extended to more broad applications, such as evaluation of anthropogenic
activities, estimation of influences of soil disturbances and long term soil evolution.