Comparison of nonstationary regional flood frequency analysis techniques based on the index-flood approach

Regional flood frequency analysis (RFFA) techniques are used in hydrological applications for estimation of design quantiles at ungauged sites or catchments with sparse observational records. The index-flood method, a popular approach for RFFA, is based on the assumption that the flood records within a homogeneous region are identically distributed, except for a site-specific index flood. Because of rapidly changing land-use patterns, human interventions, and climate change, recent studies proposed extension of the index-flood method to account for nonstationarity in flood records. This work compared index-flood–based nonstationary RFFA techniques, in both synthetically generated and real-world homogeneous regions, with sites marked by significant trends in flood records. From the data used in the analysis, it is evident that two recently proposed transformation-based approaches are more suitable compared to other methods, and can capture time-varying behavior of floods effectively.