Effect of Rainfall Temporal Distribution on the Conversion Factor to Convert the Fixed-Interval into True-Interval Rainfall

Abstract

In this study, the Weiss approach to derive the CF (the conversion factor to convert the fixed-interval annual maximum rainfall into the true-interval one) was examined and revised to consider the rainfall temporal distribution. As examples, several rainfall temporal distribution models currently being used in the rainfall-runoff analysis, along with several simple distributions such as triangular or pentagonal, were considered to derive the CF. The resulting CFs were then compared with the CFs estimated by analyzing the observed rainfall data, both in Korea and in several other countries, such as the United States, the United Kingdom, Australia, and New Zealand. The findings from this study can be summarized as follows. First, the effect of the temporal distribution of rainfall is very significant on the estimation of the CF. The CF for the impulse rainfall was the smallest at 1.0, and that for the uniformly-distributed rainfall was the highest at 1.333. Second, the CFs derived for the temporal distribution models considered in this study were higher than the empirical CFs used worldwide. Finally, it was found that, among simple distributions and temporal distribution models analyzed in this study, the quadratic functional form and the Keifer and Chu method provide the most similar CF value to the empirical CF values used in many countries mentioned above.