5th Swiss Geoscience Meeting, Geneva 2007
Grosser Aletschgletscher in the 21th century: Modelling
glacier evolution and stream-flow runoff
Matthias Huss, Daniel Farinotti, Andreas Bauder and Martin Funk
Versuchsanstalt für Wasserbau, Hydrologie and Glaziologie (VAW), ETH Zürich, ch8092 Zürich (mhuss@vaw.baug.ethz.ch)
Grosser Aletschgletscher is the largest glacier of the Alps and stores an ice
volume in the order of 15km3. Climate change in the 21th century will reduce
glacier extent significantly and alter the runoff characteristics of high alpine
catchment basins. We apply a combined glacier evolution-runoff model to the
highly glaciated catchment of Grosser Aletschgletscher. We present time-series
of mass balance, glacier extent and discharge in daily resolution for the period
2008-2100 using different scenarios for climate change.
Glacier mass balance and runoff is calculated using a distributed temperatureindex melt and accumulation model. An evaporation submodel is coupled to the
glacier model. Required input variables are temperature and precipitation in
daily time steps and a digital elevation model (DEM). The model is calibrated
using ice volume changes derived from 5 DEMs between 1880 and 1999 and
in-situ measurements of accumulation and ablation at stakes. We validate the
combined model by comparing calculated to measured monthly runoff volumes
(1922-2006). A glacier retreat model is applied in order to account for the
reduction of the glaciated area. It is based on mass conservation and
reproduces 3D spatial changes of the glacier surface geometry. The ice
thickness distribution is known from radio-echo soundings in the ablation area
of Aletschgletscher performed in the 1990s. We estimate the ice thickness for
regions not covered by measurements using a method based on considerations
of mass turn over and glacier surface characteristics.
Using a probabilistic distribution of different climate scenario runs for the
seasonal change in temperature and precipitation (Frei, 2005) we calculate the
runoff from the catchment of Grosser Aletschgletscher for the period 20082100. A stochastic internal climate variability is superimposed and provides
estimates of the uncertainty in modelled runoff due to the year-to-year
fluctuations of the meteorological variables. The annual discharge is increasing
in the next decades which is due to the release of water from glacial storage.
The enhanced future runoff in the summer months may pose an important
hazard potential especially when combined with heavy rainfalls which are
routed downstream immediately due to the low retention capacity of the bare ice
surface. In all climate projections the glacial area decreases dramatically.
However, Aletschgletscher will not have disappeared by the end of the 21 th
century. The fraction of discharge during spring and early summer increases
significantly. This shift in the peak runoff corresponds to a change from an icemelt dominated regime to a snow-melt dominated regime and may have
significant impact on the management of water resources.
REFERENCES
5th Swiss Geoscience Meeting, Geneva 2007
Frei, C. (2005). Die Klimazukunft der Schweiz - Eine probabilistische Projektion.
Available at http://www.occc.ch, 8pp.