Long-term assessment of bias adjustment in radar rainfall estimation

A comprehensive analysis of precipitation estimation by weather radar operated over hilly terrain is performed. The study is based on a nearly continuous 3-year database of weather radar observations and hourly rain accumulations from a dense rain gauge network located in southwest England. Radar rainfall processing scenarios associated with correction for systematic and range dependent errors are investigated. The focus of the study is in demonstrating the impact of radar range effects at short to medium (less than 70 km) distances and determining the significance of coupling mean-field and range-related bias adjustment in radar rainfall estimation. The investigation is performed on the basis of climatological radar rainfall statistics for selected radar sectors and radar-rain gauge comparisons over a densely instrumented medium size (135 km 2) basin located at 35-40 km from the radar. The application of the combined adjustment is shown to reduce overall error over the catchment by 24%. The analysis suggests that gauge-based radar adjustment can be properly applied only when homogeneity in the accuracy of the radar rainfall estimates with respect to range and scanning elevation is ensured.