Abstract
Abstract. The Central European floods of July 1997 and August 2002 spotlighted the need for systematic research of the relationships between synoptic-scale conditions and heavy large-scale rainfalls. Creating a set of historic events underlies such research. We defined the criterion for their selection, which is based on daily areal precipitation amounts in predefined sub-regions. To stress the hydrological responses of precipitation, the criterion expresses the temporal distribution of daily areal precipitation in a three-day period. We applied the criterion to clusters of the Czech Republic river basins that were affected by high areal precipitation almost simultaneously during individual events. Finally, we selected events with the ten highest criterion values within each cluster during the warmer half-years from 1951 to 2006. Regarding the spatial extent of heavy rainfalls, we identified a few events during which a substantial part of the Czech Republic was affected. The events include, for instance, the floods of July 1997 and August 2002 that were unique in terms of precipitation totals. The uniqueness of the event in 2002 is that it consisted of two episodes that occurred in rapid succession and demonstrated heavy rainfall that affected almost the same area. Regarding the spatial distribution of precipitation, we identified several groups of events in which heavy rainfall affected similar sub-regions of the Czech Republic. This attribute was most likely related to similar synoptic-scale conditions. In terms of the seasonal variability, the most significant events were concentrated in high summer, which is typical of orographically exposed clusters. Interannual variability of the events was characterized by two main ten-year periods with a rather low frequency of occurrence followed by the years with increased frequency. The analysis of both the hydrological responses and synoptic-dynamic conditions of the events will be the object of further research.
Highlights
Flooding is one of the most damaging natural hazards and is a complex hydrological event whose origin and development are influenced by a range of meteorological and nonmeteorological factors
Regarding the spatial extent of heavy rainfalls, we identified a few events during which a substantial part of the Czech Republic was affected
While winter floods are often caused by the combined effect of both heavy rains and the intense melting of snow, the saturation of river basins by antecedent precipitation may play a significant role during the warmer half-year (Brazdil et al, 2005)
Summary
Flooding is one of the most damaging natural hazards and is a complex hydrological event whose origin and development are influenced by a range of meteorological and nonmeteorological factors. Two main types of rain floods can, be distinguished: (i) Flash floods, usually only in the small streams, caused by convective torrential rain and (ii) floods in the major rivers produced by intense long-lasting large-scale rainfalls The latter type is conditioned by the occurrence of extensive precipitation bands associated with extra-tropical cyclones and/or atmospheric fronts (Matejka et al, 1980). We take into account precipitation amounts, and the extent of the affected area and the time concentration of precipitation Each of these factors plays a significant role in the hydrological response of precipitation in the case of large-scale floods in Central Europe. In winter, the hydrological effect of precipitation is often reduced because of the prevailing solid state of precipitation
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