NEXRAD Radar for Flood Prediction in Houston

Due to a number of hydrologic and meteorologic factors, Houston, Texas, is subject to major flooding problems. The National Weather Serviceʹs (NWS) WSR-88D radar (NEXRAD) was used to estimate the areal and spatial distribution of rainfall for three storms over the Brays Bayou watershed in Houston for hydrologic modeling purposes. Rainfall rates estimated from the NEXRAD radar compared favorably to the point rainfall measurements at the operating rain gauges in the watershed for the large October 1994 storm, but tended to overpredict the point rainfall measurements at the rain gauges for two smaller events. Using HEC-1, two model runs were made using the unadjusted NEXRAD-estimated rainfall rates and also using the rain gauge network, and the modeled outflow hydrographs were compared to the measured hydrograph for all three storms. The results from the radar proved to be as accurate, and in some cases more accurate, than the rain gauge model when predicting runoff volume, peak flow, and time of peak. Results from this research are being used to create a local flood warning system on the Brays Bayou watershed using real-time NEXRAD radar.