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Rudolph, James V ¹ ; Friedrich, Katja ²

¹ University of babyÖ±²¥app, Dept. of Atmospheric and Oceanic Sciences (ATOC)
² University of babyÖ±²¥app, Dept. of Atmospheric and Oceanic Sciences (ATOC)

A 21st century precipitation forecast for seven Swiss river basins is generated by linking high resolution (2 x 2 km2) radar-estimated precipitation observations to a global climate model (GCM) via synoptic weather patterns. The use of synoptic patterns characterizes the effect of changes in large scale circulation, or dynamic effects, on expected precipitation. In each basin observed total daily precipitation received during advective synoptic patterns is shown to be dependent on the basin’s general topographic aspect. Across all basins convective synoptic patterns follow the same trend in total daily precipitation with cyclonic patterns consistently producing a larger amount of precipitation than anticyclonic patterns. Identification of synoptic patterns from a GCM for the 21st century (Community Climate System Model Version 3.0, CCSM3) shows increasing frequency of anticyclonic synoptic patterns, decreasing frequency of cyclonic patterns, and constant frequency of advective patterns over Switzerland. When coupled with observed radar-estimated precipitation for each synoptic pattern, the changes in synoptic pattern frequencies result in an approximately 10-15% decrease in decadal precipitation over the course of the 21st century for seven Swiss river basins. The study results also show an insignificant change in the future (21st century) probability of exceeding the current (2000-2008) 95th quantile of total precipitation. The lack of a trend in exceeding the 95th quantile of precipitation in combination with a decreasing trend in total precipitation provides evidence that dynamic effects will not result in increased frequency of heavy precipitation events, but that heavy precipitation will account for a greater proportion of total precipitation in Swiss river basins by the end of the 21st century.