Malaysia has 10 weather radar stations belonging to the Malaysian Meteorological Department (MMD) that can be used to estimate rainfall distribution. A new computer program called RaDeR ver1.0 was developed to estimate the radar-derived rainfall intensities from archived raw weather radar data. The RaDeR ver1.0 performs fast estimation more than 100 times of 3D-Rapic program currently used by MMD. Since Malaysia is a tripical country with more than 60% of land area covered by forest, using the limited number of rain gauges to determine the spatial distribution of rainfall in forested watersheds may not be representative, hence not the best technique. Therefore, a VRS-RaDeR system was developed to improve mapping of the rainfall spatial distribution using virtual rainfall stations (VRS) network and the RaDeR ver1.0 program. It was found that using the development system to estimate the rainfall distribution gives better watershed runoff result than using the traditional rain gauge data.