Delineation of homogeneous regions for regional frequency analysis using statistical depth function

•Introducing statistical depth function in the delineation step of RFA procedure.•Comparing the homogeneity of region obtained by traditional and depth methods.•Improving the results by including depth in both RFA steps.

SummaryThe aim of regional frequency analysis (RFA) is to estimate extreme hydrological events at sites where little or no hydrological data are available. The delineation of sub-regions and the regional estimation within these sub-regions are the two main steps of RFA. As currently practiced, the delineation step is unrobust and subjective. To overcome these limitations, the present paper aims to propose a new robust approach for delineating homogeneous sub-regions. The proposed approach is objective and based on the concept of depth function. A data set from three geographical regions in the North-West of Italy is used to apply and compare the proposed approach with a traditional one. Results indicate that the proposed Depth-based approach leads to more homogeneous sub-regions in terms of H heterogeneity measure, and leading to more efficient quantile estimations in terms of relative bias and relative root mean square error, than those obtained by the traditional approach.