A More Efficient Rainfall Intensity-Duration-Frequency Relationship by Using an at-site Regional Frequency Analysis: Application at Mediterranean Climate Locations

Intensity-duration-frequency (IDF) relationships are the tools for obtaining design rainfall estimation. Their calculation requires rainfall data not commonly available in time. The scarce spatial information makes it difficult to perform a Regional Frequency Analysis (RFA). The objective of this paper was to establish a new method to obtain more efficient IDF relationships than those traditionally applied, by using at-site regional frequency analysis. An application to rainfall datasets from two Mediterranean climate locations (Spain and Chile) has been set up. Nine annual maximum rainfall data series (AMS) of duration from 10 min to 24 h were analyzed. The tests of Mann-Whitney for homogeneity, Wald-Wolfowitz for independence and Mann-Kendall for stationarity, were conducted to test the underlying assumptions in frequency analyses. The RFA tests identified the nine considered datasets from each location as a homogeneous region, and the suitable regional frequency distribution to establish the regional growth curves. Considering the regional index flood model, the regional growth curves were used to obtain the rainfall quantiles for the return periods and durations considered at each location Their combination with the equations obtained after correlating the mean values from the AMS and their durations permitted the obtainment of the new power-type IDF relationships.. The efficiency of the new model was evaluated by using several efficiency indexes, being more efficient and giving a better performance compared to traditional IDF models. The proposed method offers great application possibilities in Mediterranean climate areas located in the Mediterranean Catchment, California, Mexico, Central Chile, Australia and South Africa.