DEVELOPMENT AND UTILITY OF HUFF CURVES FOR DISAGGREGATING PRECIPITATION AMOUNTS

Watershed models are becoming more sophisticated and require temporal inputs of precipitation to drive the modeled hydrologic processes. Short time increments of the order of minutes are particularly needed, but these are seldom available or do not have good spatial coverage. The most widely available precipitation data in the United States are total amounts for 24-h periods. Information on the actual intensity distribution within a period of precipitation is lacking and practitioners resort to approximate methods to distribute the precipitation in time (“disaggregation”). The most common approach to disaggregate total precipitation amounts has been to use “design storms,” fixed patterns of the time distribution of precipitation intensities within a period. “Huff curves” provide a method of characterizing storm mass curves. They are a probabilistic representation of accumulated storm depths for corresponding accumulated storm durations expressed in dimensionless form. The development of Huff curves is described in the present study using precipitation data from Coshocton, Ohio because the procedure has never been documented in the literature. The potential use of these curves, the state of knowledge, and research needs for advancing the utility of Huff curves for storm disaggregation are summarized. Three approaches for using Huff curves to disaggregate precipitation totals are described: design storms (fixed patterns of intensities), stochastic simulation of within-storm intensities, and a hybrid of these two approaches. Expanded use of Huff curves as described in the latter two approaches offer opportunities for maximizing the information contained in Huff curves. There is no meaningful correspondence between NRCS design storms (Types I, IA, II, and III) and Huff curves. A computer program is available to facilitate the development of Huff curves for stimulating research into their practical use.