Mountain Hydrology Workshop, Bucharest, Romania, 26 September 2003
THE IMPACT OF CLIMATE CHANGE ON THE HYDROLOGY
IN MOUNTAINOUS REGIONS
M. Verbunt, J. Gurtz
Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology, ETH,
Zurich, Switzerland, verbunt@iac.umnw.ethz.ch
The spatially distributed hydrological WaSiM-model (Water Flow and Balance Simulation
Model) has been applied to a snowmelt dominated Swiss Alpine catchment to make a detailed
hydrological analysis of possible climate change impacts.
The Dischma catchment (43 km2) is part of the upper Rhine basin and is situated in the
eastern part of Switzerland. Its altitude ranges from 1677 to 3139 m asl. The model, driven by
observation data, was calibrated to snow water equivalent measurements and hourly discharge
observations over 1981 to 1984. The validation period was 1985 to 2000. The comparisons of
computed runoff and snow water equivalent to their observations in both calibration and
validation period show the model’s capability to simulate the hydrologic processes in this
catchment.
Monthly climate change scenarios for precipitation, temperature, wind-speed, global radiation
and vapour pressure have been used to estimate climate change impacts on the water cycle
and snow hydrology. The study of possible consequences of climate change on the water
balance components and snow water equivalent has been made spatially distributed, including
analyses for different altitudes.
The results show that the monthly and annual water cycle change considerably. Although the
annual discharges decline, they clearly increase in winter as a result of increasing liquid
precipitation. The results show further a clear decrease of snow water equivalent and
consequently a shortening of the snow cover duration. A possible impact of climate change on
the nival runoff regime in this catchment, with highest discharges in early summer and lowest
water flows in winter, could be that the runoff peaks in spring and early summer are less
pronounced due to less available snowcover for the melt. The altitudinal analysis of climate
change impacts shows that the loss snow water equivalent is highest in the upper elevation
zones.