Assessment of methods for obtaining rainfall intensity-duration-frequency ratios for various geographical areas

Abstract

Several procedures for obtaining rainfall intensity-duration-frequency (IDF) relationships for storm durations ranging from 10 min to 24 h and for several return periods were analyzed. The data recorded for the period 1966–1997 are from five different locations in southern Spain: one mountain, two inland, and two littoral stations. We analyzed the original equations of Wenzel, Bell, Chen and Témez, and other ones modified from the last two. The first step was to determine the parameters of each equation for each geographical location. Subsequently, the coefficient of variation (CV) and index of agreement (ia) of each equation were calculated in order to compare their estimations for rainfall durations of less than 2 h and less than 24 h. The results show that there is not one equation which is best suited for all the geographical areas or rainfall durations. The reference method, Wenzel apos;s equation, is the best for rainfall periods of less than 24 h, but only for the littoral and inland geographical areas. If Wenzel apos;s equation is not taken into account, the modified Témez equation proved to be the best at generating series for mountain areas and for the two rainfall periods studied. Therefore, in a regional study of rainfall durations of less than 24 h, where only 24 h data are available, and with littoral, inland and mountain areas, the modified Témez equation is strongly recommended.