High-resolution spatial analysis of the variability in the subdaily rainfall time structure

Abstract

The paper is motivated by the generally large variability in the rainfall time structure during the events with high subdaily precipitation totals in Czechia, which should be taken into account when designing water management systems to handle precipitation. The presented spatial analysis of the variability in the rainfall time structure is based on the regional frequency analysis of the 6-h totals with a spatial resolution of 1 km. The totals are quantified with the synergy method using the weather-radar-derived precipitation intensities and the totals measured by rain gauges. The frequency analysis employs the progressive and robust region-of-influence method. Instead of only one design storm hyetograph, each site is characterized by the possible occurrence of six hyetographs that are synthetized from the heavy rainfalls in Czechia. The percentage of individual hyetographs for a given design precipitation depth is assessed through the combination of the frequency analyses of the totals with respect to and regardless of the course of precipitation. The spatial heterogeneity in the percentages is significantly affected by the topography and amplifies with the increasing return period of the totals. The six synthetic hyetographs are represented relatively evenly in the lowlands. In contrast, the mountainous areas are characterized by a notable increase in the percentages of events of long-lasting steady rain, which are triggered by their circulation causes together with the significant role of the orographic precipitation enhancements, particularly through the windward orographic lifting, which is mainly on the northern and eastern slopes of the mountains. Future research on the dependence between the return period of the events of a specific precipitation course and the magnitude of the antecedent totals might be even more applicable to hydrological modeling in small catchments.