To reflect two severe climate-induced changes in land cover, Nina Köplin, Bruno Schädler, Daniel Viviroli and Rolf Weingartner applied scenarios of glacier retreat and forest cover increase for the period 2074 - 2095. The respective climate scenarios were derived from ten regional climate models. Altogether, 15 mountainous catchments in Switzerland were analysed, exhibiting different degrees of glaciation during the control period (1984 - 2005) and different degrees of forest cover increase under scenarios of change.
The results show that even an extreme change in forest cover is negligible with respect to changes in runoff. But on the other hand this change is crucial as soon evaporation or soil moisture are concerned. For changes that concern 35 % of the catchment area or more, the effect of forest change on summer evapotranspiration is equally or even more important than the temperature change. For catchments with a glaciation of 10 % or more in the control period, the glacier retreat significantly determines summer and annual runoff.
The most important source of uncertainty in this study, though, is the climate scenario. The authors, in their article in Hydrology and Earth System Sciences, therefore highly recommend to apply an ensemble of climate scenarios in impact studies. The novel way of additionally including glacier and forest cover changes in hydrological climate-impact studies provides insight into the question whether or not it is necessary to account for land cover changes as part of climate change impacts on hydrological systems.
