Effect of Return Period on Normalized Rainfall Distributions in the United States

Abstract

The assumption that normalized 24-h rainfall distributions are independent of return period is investigated. The results of this study show that this assumption is justified in the interior region of the eastern United States, but in other parts of the country, notably the eastern coastal states and the western United States, the assumption can lead to errors of up to ±2% in rainfall amounts within various time intervals in the 24 h event. The greatest errors occur for short time intervals and for return periods that differ markedly from the return period used in deriving the normalized rainfall distribution. Caution should be exercised when applying regional Natural Resources Conservation Service (NRCS) 24-h rainfall distributions, which are based on 25-year return periods, to catchments at lower return periods, such as 1–1 years, with times of concentration less than 3 h.