ALBERT

Description: Instationarity of the time series of annual peak discharge is demonstrated for the Enz River Basin/Black Forest, and the upper Danube Basin in Germany. The reason for this is a dramatic increase in frequency and persistence of the large-scale atmospheric circulation type “West cyclonic” (Wz) in winter (Dec.- Feb.). During the observation period (1926–1995) nearly all extreme flood events in the Enz and Danube River Basins have been caused by circulation type “Wz” during winter. For the atmospheric circulation nonparametric tests show that instationarity starts for the time series (1881–1995) of winter-Wz-frequencies (Dec.- Feb.) in the year 1972. The change-point of the time series of the annual peak discharges of the Enz River (1932–1995) and the upper German Danube Basin (1926–1995) can be detected for the year 1976. Thus instationarity is caused by a changed winter climate.