Weather Patterns and Hydro-Climatological Precursors Of
Meteorologische Zeitschrift, Vol. 21, No. 6, 531–550 (December 2012) Open Access Article Ó by Gebru¨der Borntraeger 2012 Weather patterns and hydro-climatological precursors of extreme floods in Switzerland since 1868 Peter Stucki1,*, Ralph Rickli1, Stefan Bro¨nnimann1,2, Olivia Martius1,2, Heinz Wanner1,2, Dietmar Grebner3 and Ju¨rg Luterbacher4 1Institute of Geography, University of Bern, Switzerland 2Oeschger Centre, University of Bern, Switzerland 3Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland 4Department of Geography, Justus-Liebig-University Giessen, Germany (Manuscript received February 21, 2012; in revised form October 30, 2012; accepted October 31, 2012) Abstract The generation of 24 extreme floods in large catchments of the central Alps is analyzed from instrumental and documentary data, newly digitized observations of precipitation (DigiHom) and 20th Century Reanalysis (20CR) data. Extreme floods are determined by the 95th percentile of differences between an annual flood and a defined contemporary flood. For a selection of six events between 1868 and 1910, we describe preconditioning elements such as precipitation, temperature, and snow cover anomalies. Specific weather patterns are assessed through a subjective analysis of three-dimensional atmospheric circulation. A focus is placed on synoptic-scale features including mid-tropospheric ascent, low-level moisture transport, propagation of cyclones, and temperature anomalies. We propose a hydro-meteorological classification of all 24 investigated events according to flood-generating weather conditions. Key elements of the upper-level synoptic-scale flow are summarized by five types: (i) pivoting cut-off lows, (ii) elongated cut-off lows, (iii) elongated troughs, (iv) waves (with a kink), and (v) approximately zonal flow over the Alpine region.
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