Drainage density in relation to precipitation intensity in the U.S.A.

Previous studies have suggested that drainage density D varies directly with precipitation intensity PI. However, an analysis of data from the U.S.A. indicates that the relationship between D and PI is inverse, at least where PI >50 mm24 hr. — that is, in all but desert climates. This inverse relationship is consistent with the direct relationship between PI and mean annual precipitation PM and the inverse relationship between D and PM reported in 1972 by Abrahams. Drainage density varies directly with PI and PM via runoff intensity and inversely with these precipitation variables via the vegetation and soil cover. Previous studies of the relationship between D and PI either held PM constant or adjusted for differences in PM. Because the vegetation and soil cover are closely related to PM, it is suggested that these studies inadvertently controlled for differences in the vegetation and soil cover. Consequently, the effect of PI on D was predominantly through runoff intensity and hence D was found to vary directly with PI.