Regional extreme rainfall estimation in the Middle Black Sea Region, Turkey

The occurrence probabilities of heavy rainfall that cause flood events have an essential role in designing water-related structures and water resource management. In many cases, data for analysis are either not available or are insufficient for reliable design of water-related structures. Regional frequency analysis is usually preferred to provide design information in sites with especially inadequate data available. Our study applied L-moment procedures to annual maximum rainfall series from 70 gauging stations in the Middle Black Sea Region (MBSR) of Turkey to estimate regional rainfall quantiles. The first attempt for regionalization aimed to evaluate the entire area as an homogeneous region. The sub-regions were initially defined with the ward’s clustering algorithm due to the presence of discordant sites under a presumption of a single homogeneous region. In compliance with the results of the discordancy and heterogeneity measures, the most promising classification was achieved with six clusters (sub-regions) that satisfied the homogeneity condition as “acceptably homogeneous”. It was decided that the GEV and GLO distributions in five sub-regions, the GNO distribution in four sub-regions, and the PE3 distribution in three sub-regions, were acceptable as regional frequency distributions. In comparison, GPA was not a candidate distribution in any of the six sub-regions.