Weather types and geographical distribution of intense rainfall

The spatial rainfall distribution is affected by the type of the prevailing weather situation as well as by local geographical factors, such us orography and latitude. The study of the areal distribution of rainfall is important especially when physiographic and climatological conditions vary over the same region causing different rainfall regimes. In this research, the influence of the prevailing weather type to the geographical distribution of the intense daily rainfall is studied. The study area is the Sterea Hellas region (Central Greece) and consists of three (among the fourteen) different water districts of Greece. The Pindos mountain chain in the west side of this region gives rise to heavy orographic rainfall and causes a wetter rainfall regime as compared with that of the east side. Daily data from 71 rain gages and hourly data from three rain recorders over a 20 year period are used. From these data sets, the intense rainfall events were extracted and analyzed. The intense rainfall days are classified according to the prevailing weather type using a daily calendar of synoptic weather types in Greece. Several methods (also including the available tools of a Geographical Information System) are used for the analysis and comparison of rainfall distributions. The results of these methods are statistically analyzed to trace similarities in geographical distribution of rainfall produced by a specific weather type, and dissimilarities in the distribution of rainfall produced by different weather types. Overall, the analysis shows that different weather types affect the location and other characteristics of rainfall in the study area.