Spatial patterns and time distribution of Central European extreme precipitation events between 1961 and 2013
Abstract
Precipitation extremes always have an area-related effect, emphasizing the need for a spatial assessment of extreme precipitation events that sometimes show similar behaviour in precipitation patterns due to recurring synoptic features. Our study investigates spatial patterns in the extreme precipitation events (EPEs) that occurred in central Europe between 1961 and 2013.
As many as 53 maximum events were selected by the weather extremity index (WEI), reflecting simultaneously the spatial extent and the return periods of t day precipitation totals within an event-adjusted study area. The extremity of the EPEs is further evaluated at two lower spatial levels, the main river basins (the Rhine, Weser/Ems, Elbe, Danube, and Oder) and 20 smaller subcatchments, which enables a more detailed study of the events' spatial structure and similarity.
A correlation analysis demonstrated that heavy precipitation occurs simultaneously not only in neighbouring subcatchments but also in rather distant regions with similar orientations of mountain ranges (e.g., in the Elbe-a and Danube-b subcatchments). In contrast, strong negative correlations appeared between several subcatchments in the Oder and Rhine River basins, which exclude heavy precipitation from occurring simultaneously in both basins.
Similar spatial patterns are obvious among precipitation extremes; using the relative WEI values as the similarity measure, agglomerative hierarchical clustering detected two well-separated groups of events, namely, W-CE and E-CE, affecting mainly the western and eastern parts of central Europe, respectively. A finer division of the EPEs distinguished five clusters of events with different spatio-temporal characteristics.
Only two clusters, ED (Elbe-Danube) and O (Oder), were represented among the top 10 central European EPEs, which occurred exclusively from the end of May to the beginning of September. Three other clusters consisted of generally lower extreme events rather equally distributed throughout the year.