Precipitation areal-reduction factor estimation using an annual-maxima centered approach

The adjustment of precipitation depth of a point storm to an effective (mea n) depth over a watershed is important for characterizing rainfall-runoff r elations and for cost-effective designs of hydraulic structures when design storms are considered. A design storm is the precipitation point depth hav ing a specified duration and frequency (recurrence interval). Effective dep ths are often computed by multiplying point depths by areal-reduction facto rs (ARF). ARF range from 0 to 1, vary according to storm characteristics, s uch as recurrence interval; and are a function of watershed characteristics , such as watershed size, shape, and geographic location. This paper presen ts a new approach for estimating ARF and includes applications for the 1-da y design storm in Austin, Dallas, and Houston, Texas. The approach, termed "annual-maxima centered," specifically considers the distribution of concur rent precipitation surrounding an annual-precipitation maxima, which is a f eature not seen in other approaches. The approach does not require the prio r spatial averaging of precipitation, explicit determination of spatial cor relation coefficients, nor explicit definition of a representative area of a particular storm in the analysis. The annual-maxima centered approach was designed to exploit the wide availability of dense precipitation gauge dat a in many regions of the world. The approach produces ARF that decrease mor e rapidly than those from TP-29. Furthermore, the ARF from the approach dec ay rapidly with increasing recurrence interval of the annual-precipitation maxima. (C) 2000 Elsevier Science B.V. All rights reserved.