Regional frequency analysis of heavy precipitation in the Czech Republic by improved region-of-influence method

The region-of-influence (ROI) approach is implemented for modelling the probabilities of heavy 1-day and 5-day precipitation amounts in the Czech Republic. Compared to the previous study for Slovakia (Gaál et al., 2008), an improved ROI methodology that makes use of a regional homogeneity test for assigning sites to pooling groups, is applied. Two basically different approaches to forming the pooling groups in which groups of sites are gradually built up and cut down, respectively, are combined. A sensitivity analysis, which examines the performance of the ROI models after changing the set of input site attributes that serve for determining the sites' similarity, is carried out. Finally, several frequency models that include the ROI pooling schemes, a conventional model based on fixed regions, and an at-site analysis are compared by means of Monte Carlo simulations. We conclude that, regardless of the duration of precipitation, the ROI pooling scheme based on the actual proximity of sites (latitude and longitude) outperforms the other frequency models in terms of the root mean square error of the growth curves.