Many studies have been conducted on the use of weather radar in urban hydrology driven by the desire for rainfall measurements at high spatial and temporal resolution. Hydrological data for selected flood events in the Cranbrook urban catchment (approximately 910 ha) near London, UK were used to investigate the impact of different spatial and temporal resolutions of radar rainfall estimates on urban hydrology. In this study, the radar rainfall in raw polar format was converted to different high spatial resolution Cartesian formats, ranging from 250-m to 1-km spatial resolution. For each spatial resolution, the rainfall data were resampled to various temporal resolutions. The preliminary results showed that precipitation data in the polar cells and converted Cartesian grids at different spatial resolutions were fairly similar in the time and frequency domains. This precludes the exploitation of higher resolution data in urban modeling because of the lack of additional information content in the dual-polarization radar signal. Recommendations for applying high-resolution Cartesian precipitation data to real-time flood forecasting on an urban catchment are provided and suggestions for further investigation are discussed.