This document summarizes a study on the impacts of climate change on hydrology in Switzerland. It finds that: 1) Snow cover depth will decrease and glacier melt will intensify as glaciers decrease in area due to rising temperatures. 2) The timing of peak annual river runoff is projected to occur 3-6 weeks earlier on average by the end of the century. 3) Annual river runoff is projected to decrease slightly (2.5-6.4% less than the reference period) in heavily glacierized catchments like the Engadin region by the 2070-2099 period despite large uncertainties from climate models.

1. Climate Change and Hydrology in Switzerland
Luzi Bernhard, Massimiliano Zappa and Norina Andres
Swiss Federal Institute for Snow, Forest and Landscape Research WSL | CH-8903 Birmensdorf Switzerland
Introduction
Methods and validation
Results
Conclusions
International Glacier Forum | Huaraz, Perú | 1 - 4 July 2013
0200400600800
Engadi n
MeanSWE[mm]
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008
PREV AH si m
203 Stations
133 Stations
110 Stations
0100200300400
Engadin: < 1500 m (4.74 % of the area)
MeanSWE[mm]
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008
0200400600800
Engadin: > 1500 m (95.26 % of the area)
MeanSWE[mm]
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008
Paul, F., Maisch, M., Rothenbühler, C., Hoelzle, M. & W. Haeberli, 2007. Calculation and visualisation of future glacier extent in the Swiss Alps by means of hypsographic modelling. Global and Planetary Change, 55
Stahl, K., Moore, R. D., Shea, J. M., Hutchinson, D. & A. J. 2008. Coupled modelling of glacier and streamflow response to future climate scenarios. Water Recources Research, 44
van der Linden, P. & J. Mitchell 2009. ENSEMBLES: climate change and its impacts: summary of research and results from the ENSEMBLES project. Met Office Hadley Centre
The projected climate change might have significant impacts on snow cover and glaciers, and thus on water resources in the European Alps. Apart from the actual climate scenarios, further rel-
evant basic conditions have to be considered for the calculation of the hydrological climate change impact. Rapid glacier retreat in the Alps since the middle of the 70ies had to be taken into ac-
count and it was necessary to consider the change in glacier area in this simulation experiment. For the coupled application with climate scenarios, this procedure is classifed as mandatory (Stahl
et al. 2008).
In this case study, the local meteorological changes and the resulting changes in the glaciation, the snow cover and the discharge for the time periods 2021 - 2050 and 2070 - 2099 are simulated
and compared to the control period 1980 - 2009.
We assimilated regional climate model data (ten scenarios) of the European project ENSEMBLES (van der
Linden et al. 2009), which base on the emission scenario A1B (moderate global warming). To reflect the
estimated local climate change in a large basin, the climate scenarios were fed into a hydrological model
by using the delta change method on a daily basis for the statistical downscaling of temperature and pre-
cipitation scenarios.
For future scenarios of the glaciation, the original state of 1973 was continuously reduced in five-year in-
crements with a shrinkage model of Paul et al. (2007). The model is based on the simple assumption that
the equilibrium line altitude (ELA) increases respectively to the increase of air temperature. Thereby the
area of the accumulation regions of the glaciers reduces, which results in a change of the glacier length.
The comparison with a recently developed snow product at the WSL institute for Snow and Avalanche Re-
search SLF (Jonas et al. 2009) shows a satisfying simulation result of the snow cover. The adjacent
figure shows the SLF-product and our simulation for the catchment of the Swiss river Inn. Snow-poor (e.g.
1990 and 1996) as well as snow-rich (e.g. 1982 and 1999) winters are well differentiated. Especially after
2000 the yearly simulated maximal Snow Water Equiwalent (SWE) value fits well the SLF-product.
Simulated (black) and observed (colored) mean snow water equivalent (SWE) in the Engadin
(top: whole region; middle: below 1500 m a.s.l.; below: above 1500 m a.s.l.)
The table below summarizes the annual mean of the calculations for the control period 1980 - 2009 as well as the
expected changes in the two scenario periods (2021 - 2050 and 2070 - 2099). Noticable is the change in the near
future regarding the percentage of the glacier melt compared to total runoff (-22.4%), which should even out for the
far future. On the contrary the percentage of the snowmelt will decrease in the first part of the current century (-
15.6%) and the negative trend will be increased in the second period (-38.6%). The changes in the yearly mean values
of the total runoff and the evaporation are small. Even though changes in the annual mean seem to be low, seasonal
changes and the resultant consequences of the climate signal on the water balance have relevant impacts.
Natural water balance in Switzerland for the control period and the two scenario periods (P-kor: corrected pre-
cipitation; EREA: evaporation; RGES: total runoff; GLAC: glacier melt; P-SME: snow melt; DS: change in storage)
The adjacent figures shows a bivariate map of the two variables snowmelt and total runoff; above for the control
period and below for the mean scenario period 2070 - 2099.
In the pixel map representing the control period 1980 – 2009, orange and reddish coloring can be observed in the north-
ern and northwestern part of Switzerland, which means that in these regions the total runoff is low and 20 – 60% of the
runoff originate from snowmelt. The low summer precipitations percolate and do not contribute to runoff. The regions of
the main chain of the Alps, the Engadin and the canton Valais show a totally different pattern. The valleys of the canton
Grisons and Valais contribute little to runoff, but runoff is highly characterized by snowmelt. By increasing altitude, on
the one hand snowmelt increases, because a high fraction of the yearly precipitation is snow and on the other hand
total runoff increases highly.
The scenario period 2070 – 2099 shows a similar pattern like the control period. Noticeable is mainly the general de-
crease of the percentage of snowmelt compared to the total runoff, which goes in line with the expected increase of
the snow line. Additionally, in precipitation-rich regions like the Prealps and the canton Ticino the contribution of snow-
melt to the total runoff will almost disappear, because even during the winter a close snow cover over a longer time
period will hardly be present.
Based on current climate predictions and glacier scenarios, the hydrological changes were calculated for the large catchments of Switzerland for the time periods 2021 - 2050 and 2070 - 2099. The
hydrological model PREVAH, which was successfully used since ten years in glaciated and snow-affected regions, shows also a good performance in this project.
Even though forecast of precipitation and glacier change are still connected with great uncertainties, clear statements about hydrology can be made: The snow cover depth will decrease, glacier melt
will intensify, glacier area will decrease and there will be distinctive change in the yearly hydrograph curve of the total runoff (the maximum will be 3 - 6 weeks earlier).
The adjacent figure shows the projections of the mean yearly runoff in the region Engadin as an example for the chang-
ing water balance. Quantitatively, highest runoff wil hardly change during an average year. But highest runoff will arrive
up to one month earlier, i.e. beginning of June instead of mean June to beginning of July. In a normal year (dependend on
the climate model chain), the whole yearly runoff will decrease for the near future (2.5%), resp. for the far future (6.4%)
compared to the reference period. The high spread shows the uncertainty due to the propagation of the ten climate
scenarios in the hydrologcical system.
Projection of the mean runoff of the river Inn close to Martina in the region of Enga-
din. Control period (1980 - 2009) in black, climate scenarios (2070 - 2099) in color
Canton Valais
Canton Grisons
Canton Ticino
Bivariate representation of water resources in Switzerland. Total runoff vs. frac-
tion of snowmelt (above: 1980 - 2009, below: mean scenarios 2070 - 2099)
Engadin