Performance evaluation of high-resolution rainfall estimation by X-band dual-polarization radar for flash flood applications in mountainous basins

Different relations between surface rainfall rate R and high-resolution polarimetric X-band radar observations were evaluated using a dense network of rain gauge measurements over complex terrain in Central Italian Alps The specific differential phase shift K-DP rainfall algorithm (R-KDP) although associated with low systematic error It exhibits low sensitivity to the spatial variability of rainfall as compared to the standard algorithm (R-STD) that is based on the reflectivity-to-rainfall (Z-R) relationship On the other hand the dependence of the reflectivity measurement on the absolute radar calibration and the ram-path radar signal attenuation introduces significant systematic error on the Rem rainfall estimates The study shows that adjusting the Z-R relationship for mean-field bias determined using the R-KDP estimates as reference is the best technique for acquiring unbiased radar-rainfall estimates at fine space-time scales Overall the bias of the R-KDP-adjusted Z-R estimator is shown to be lower than 10% for both storm cases while the relative root-mean-square error is shown to range from 0 6 (convective storm) to 09 (stratiform storm) A vertical rainfall profile correction (VPR) technique is tested in this study for the stratiform storm case The method is based on a newly developed VPR algorithm that uses the X-band polarimetric information to identify the properties of the melting layer and devices a precipitation profile that vanes for each radar volume scan to correct the radar-rainfall estimates Overall when accounting for the VPR effect there is up to 70% reduction in the systematic error of the 3 degrees elevation estimates while the reduction in terms of relative root-mean-square error is limited to within 10% (C) 2010 Elsevier B V All rights reserved