Regionalisation of Air-Mass and Frontal Precipitation Occurrence in Europe

Abstract

Spatial and seasonal variability in precipitation-prone factors in Europe leads to a variable frequency of each origin-based extreme precipitation type. This chapter synthesises the results of the occurrence of each of these. Cluster analysis of k-means method and carefully selected grouping variables were used to identify six groups of stations (regional groups) in each season characterised by different patterns of occurrence of origin-based extreme precipitation types. A clear spatial order of their occurrence suggests an existence of regularities that govern the occurrence of origin-based precipitation types in Europe. Some of the groups involve scattered stations, but such distribution, far from random, is a result of specific local influences on the processes leading to the development of extreme precipitation and on their volume. In summer, air-mass precipitation dominates three regional groups in Sothern Europe. In the southernmost of them the air-mass type accounts for nearly 70 % of extreme precipitation. Precipitation associated with the passage of different fronts represents the largest proportion of extreme precipitation in winter, when cyclone travel reaches its highest speeds.