Estimation of Depth-Area Relationships using Radar-Rainfall Data

Abstract

Depth-area relationships, such as those published by the National Weather Service in TP 40 and the NOAA Atlas 2, enable conversion of point rainfall depths to areal average depths for the same storm duration and recurrence interval. This problem of conversion is most germane to hydrologic analyses for moderate to large drainage basins, where point rainfall depths are not representative of the spatial distribution of a storm event. Historically, depth-area relationships have been developed on the basis of data from dense networks of recording gauges. However, with the ongoing accumulation of radar-rainfall records, radar-rainfall data represent an alternative to gauging data. This paper summarizes what is believed to be the first study made under the auspices of the National Weather Service (NWS) for evaluation of the potential of NEXRAD radar-rainfall data for development of geographically fixed depth-area relationships. Objectives were to evaluate the use of radar-rainfall data for development of depth-area relationships and to identify potential obstacles that might hinder use of such data. Data analyzed for this study are those recorded for the Arkansas-Red Basin River Forecast Center (ABRFC), and span the period of time from May 1993, to September 2000. Conclusions of this study are that data heterogeneities and shortness of data records are major factors limiting development of depth-area relationships on the basis of radar-rainfall data. Possible biases in radar estimates of extreme rainfall are also of concern. Depth-area curves developed for the ABRFC, presented herein, are reasonably consistent with those presented in NWS publications but should only be considered as preliminary.