A derived flood frequency distribution for correlated rainfall intensity and duration

A derived flood frequency distribution (DFFD) combines a stochastic rainfall model with a deterministic rainfall–runoff model to obtain a physically based probability distribution of flood discharges. Previous DFFD studies have either assumed that rainfall intensity and duration are independent or negatively correlated. This study is more general than previous studies because it accommodates both positive and negative correlations between rainfall intensity and duration. Rainfall–runoff processes are modeled using a φ-index infiltration model and a geomorphoclimatic instantaneous unit hydrograph. Applications to four Indian watersheds and one US watershed demonstrates that (1) the correlation of rainfall intensity and duration has an important impact on the DFFD and (2) the DFFD provides a potentially useful alternative for estimating flood flow quantiles at ungaged sites.