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Expert views - Hartmut GRA├čL (Former Director of the Max-Plank Institute, Germany and consultant of the Bavarian Government)

2012-03-12
 
Hartmut GRAßL (Former Director of the Max-Plank Institute, Germany and consultant of the Bavarian Government)

 

Will the Water Towers for Lowlands become less high?

Mountains are the water towers for lowlands. Even if total amount of precipitation might not shrink in a mountain range during the rapid ongoing anthropogenic climate change, two further climate processes will strongly impact on the river discharge, especially in lowlands: Firstly, higher evapo-transpiration caused by higher temperatures, amplified by above average warming at higher altitudes, will reduce river discharge on average and secondly, less solid precipitation might increase flood frequency and severity but not annual discharge.

For the European Alps with a projected tendency for less precipitation in the coming decades, most significant in summer, the consequences for the major rivers Danube, Po, Rhone and Rhine are: lower overall discharge, more threatening floods, more extreme low discharge in late summer and autumn. Overall, the Alps will become a less reliable water tower for the lowlands. Adaptation should start now and not only after the next new weather extreme developing into a regional catastrophe.