The Adjustment of Radar Estimates of Storm Mean Rainfall with Rain Gage Data

Abstract

Data from two dense rain gage networks in Illinois and Oklahoma were used to evaluate the feasibility of improving radar estimates of storm mean rainfall through the use of surface rain gage data to modify the radar-rainfall equation for specific storm conditions. Data were used from 19 storms and the evaluation restricted to warm-season, unstable precipitation and to the use of 10-cm radar. Evaluations were made of 1) the optimum accuracy which could be expected from radar measurements of rainfall on an ungaged area when rain gage data on adjacent gaged areas are used for adjustment of the radar estimates, and 2) the accuracy obtainable from adjustments of radar estimates with rain gage data from within the area of interest, based upon various rain gage densities in the sampling area. It was concluded that the normal climatic network is inadequate for modification of the radar-rainfall equation in warm-season storms in the Midwest if a relatively accurate estimate of storm mean rainfall is needed. However, comparison of isoecho and isohyetal patterns showed that the correspondence of radar and rain gage patterns was much better with 10-cm radar than it had been in earlier studies with 3-cm radar. It is recommended that future efforts be concentrated on improving direct measurements of rainfall from radar echo presentations.