This study analyses the uncertainty induced by the use of different
state-of-the-art climate models on the prediction of climate-change
impacts on the runoff regimes of 11 mountainous catchments in the
Swiss Alps having current proportions of glacier cover between 0
and 50%. The climate-change scenarios analysed are the result of
19 regional climate model (RCM) runs obtained for the period 2070?2099
based on two different greenhouse-gas emission scenarios (the A2
and B2 scenarios defined by the Intergovernmental Panel on Climate
Change) and on three different coupled atmosphere-ocean general circulation
models (AOGCMs), namely HadCM3, ECHAM4/OPYC3 and ARPEGE/OPA. The
hydrological response of the study catchments to the climate scenarios
is simulated through a conceptual reservoir-based precipitation-runoff
transformation model called GSM-SOCONT. For the glacierized catchments,
the glacier surface corresponding to these future scenarios is updated
through a conceptual glacier surface evolution model.
The results obtained show that all climate-change scenarios induce,
in all catchments, an earlier start of the snowmelt period, leading
to a shift of the hydrological regimes and of the maximum monthly
discharges. The mean annual runoff decreases significantly in most
cases. For the glacierized catchments, the simulated regime modifications
are mainly due to an increase of the mean temperature and the corresponding
impacts on the snow accumulation and melting processes. The hydrological
regime of the catchments located at lower altitudes is more strongly
affected by the changes of the seasonal precipitation. For a given
emission scenario, the simulated regime modifications of all catchments
are highly variable for the different RCM runs. This variability
is induced by the driving AOGCM, but also in large part by the inter-RCM
variability. The differences between the different RCM runs are so
important that the predicted climate-change impacts for the two emission
scenarios A2 and B2 are overlapping.