The Estimation of Rainfall for Flood Forecasting Using Radar and Rain Gage Data

Abstract

Abstract : An inadequate knowledge of the magnitude and spatial distribution of precipitation is often a major limitation in developing accurate river-flow forecasts for use in reservoir operations Digitized weather radar data can provide useful information regarding the spatial distribution of rainfall, although radar-based estimates of rainfall may be in error due to several factors. The use of radar-rainfall data in combination with rain gage measurements may improve rainfall estimates over those based on either form of measurement alone. This improvement is accomplished by adjusting, or 'calibrating', radar-rainfall data with data from rain gages situated within the radar 'boundary'. A set of rainfall analysis software that incorporates this methodology has been developed by the U.S. Army Corps of Engineers Hydrologic Engineering Center to aid hydrologists in making real-time water control decisions. The rainfall-analysis software retrieves real-time radar-rainfall data from a National Weather Service RADAP II (Radar Data Processor), and rain gage measurements from data collection platforms via the Geostationary Operational Environmental Satellite (GOES). The radar data from the RADAP II is 'calibrated' with the rain gage data using a simple Kriging technique. Subbasin- average rainfall is then computed from the calibrated data and stored in a data base file subsequent use by a river-flow forecast model. Graphics programs aid in the evaluation of the data. This software system has been implemented for a few pilot watersheds in Oklahoma.