Radar rainfall error variance and its impact on radar rainfall calibration

The high degree of uncertainty in radar rainfall estimation is caused by the variability in the vertical profile of reflectivity, the errors in measurements of radar reflectivity, conversion of reflectivity to rainfall rate, and the error of using point rain gauge rainfall in representing mean-areal rainfall of a radar grid size in the radar rainfall calibration. Presented here is an approach that explicitly takes into account the variations in reliability of radar rainfall estimates associated with range from the radar in calibrating of Z-R relationship. The reliability of radar rainfall estimates is calculated from the proposed climatological variance of radar rainfall error model that accounts for rainfall intensity, nature of rainfall event and number of pulses averaged in obtaining a reflectivity pixel value. Modifications to the parametric and probability matching methods (PMM) are proposed to account for the reliability of the radar rainfall estimates at the gauge locations. Six months of reflectivity-rain gauge data from the Kurnell radar in Sydney, Australia are used to test the model. The result shows the improvements in accuracy of radar measurements of rainfall by incorporating the reliability of radar rainfall estimates in the PMM are about 10% and 5% compared with the conventional PMM and parametric Z-R relationship method, respectively. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.