Seasonality of mean and heavy precipitation in the area of the Vosges Mountains: dependence on the selection criterion

摘要

The seasonal distribution of mean precipitation and heavy rainfalls during 1960-2013 was analysed based on daily precipitation totals from 168 rain gauging stations in the Vosges Mountains area, north-eastern France. Concerning mean precipitation, an ancient Hrudika's index designed as a half-time of precipitation during a year, surprisingly well expresses the seasonality of precipitation and its clear correlation with the mean annual totals in the studied region. The annual course of mean precipitation leads to a distinction of four groups of stations with respect to the position of stations: MT, mountainous stations with maxima of precipitation in winter and an overall highest mean annual totals; LSp, stations situated on leeward slopes of the Vosges Mountains with two maxima of precipitation (primary in winter and secondary in summer); URP, leeward stations located in the Upper Rhine River Plain with the most humid summer season, and the lowest mean annual totals; WSd, windward stations not influenced by the Vosges Mountains, with relatively evenly distributed precipitation, and slight maxima in autumn. For the heavy precipitation, 1-10-days totals have been considered to be heavy' subsequent to applying the three common methods - peaks over threshold (POT), block maxima (BM), and return period estimates based on generalized extreme value distribution. Varying criteria have been employed. The BM method for annual maxima indicates that the heavy rainfall generally occurs during the most humid season although it can also occur anytime during the year. The POT and return period estimates methods reveal that the seasonality of extremes is threshold-dependent and that probably the threshold sensitivity is also related to the degree of orographic influence - higher occurrence of summer events in the lee while lesser occurrence of winter events in mountains, at higher threshold and shorter duration of event.