A comparison of gauge and radar-derived rainfall in a land falling typhoon in Taiwan

Precipitation data is generally collected from rain gauge stations. However, each measurement represents only the amount of rainfall at that particular spot, not precipitation in the surrounding area. Radar approaches are considered to offer a good spatial description of precipitation, but hardly predict precipitation quantities with acceptable accuracy. To enhance our understanding of the properties of precipitation in this study, high resolution radar-rainfall estimates are compared with ground observations for an extreme precipitation event. The Taipei City area and the Shihmen reservoir watershed, situated in northern Taiwan, were chosen as the study sites, and the passage of Typhoon Nari through these areas on September 16-18, 2001, was taken as the case study event. It was concluded that radar reflectivity from the Wufenshan radar station can be helpful for identifying precipitation variations during the passage of a land falling tropical cyclone. Spots with extreme rainfall can be identified when radar approaches are performed, but not based on gauge approaches, although compared to the gauge approaches to the radar-estimated rainfall over the investigated domain tended to be overestimated. The divergence between radar-rainfall and gauge-rainfall can be identified via subwatershed investigations.