© Author(s) 2007. This work is licensed under a Creative Commons License. Natural Hazards and Earth System Sciences Extreme heat and runoff extremes in the Swiss Alps

Abstract. The hydrological response of Swiss river basins to the 2003 European summer heatwave was evaluated by a combined analysis of historical discharge records and spe-cific applications of distributed hydrological modeling. In the summer of 2003, the discharge from headwater streams of the Swiss Central Plateau was only 40%–60 % of the long-term average. For alpine basins runoff was about 60%–80% of the average. Glacierized basins showed the opposite be-havior. According to the degree of glacierization, the average summer runoff was close or even above average. The hydro-logical model PREVAH was applied for the period 1982– 2005. Even if the model was not calibrated for such extreme meteorological conditions, it was well able to simulate the hydrological responses of three basins. The aridity index φ describes feedbacks between hydrological and meteorologi