This paper aims to determine the accuracy of composite polarimetric variables, horizontal polarization (Z_H), differential reflectivity (Z_DR), and specific differential phase shift (K_DP), and rainfall rates derived from a network of four X-band polarimetric radar stations during localized convective precipitation over Tokyo on 28 September 2010 by comparison with data from a Joss–Waldvogel disdrometer and a surface rain gauge network. The four X-band polarimetric radars were complementary with respect to signal extinction, and they yielded composite maps of the polarimetric radar parameters and rainfall rates. The composite maps were validated by cross-comparison of data from the four individual radar stations, and by ground-truthing with surface observations. The raindrop size distribution (median volume diameter and normalized number concentration) was estimated from the composite maps of polarimetric parameters, and validated by the disdrometer data. We found that composite polarimetric radar parameters can provide useful information, not only for hydrological applications, but also for microphysical analysis.