Generalized Rainfall - Duration - Frequency Relationships

Rainfall-duration-frequency estimates for engineering purposes are usually subject to large sampling errors and extensive generalizations of the basic data are therefore advantageous from the point of view of estimation efficiency. Relationships between high-intensity rainfall values for durations up to 2 hr and return periods up to 100 years are appropriately expressed by means of depth-duration and depth-frequency ratios. These ratios are shown to have surprisingly consistent values in such diverse places as Alaska, Hawaii, Puerto Rica, South Africa and Australia, as well as the contiguous United States, and it is suggested that a physical explanation exists for such consistencies. The data may be conveniently generalized with one of several alternative depth-duration-frequency functions which should be useful for estimates in regions of limited data.