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In Tokyo metropolitan area, the flood risk is increasing due to social and environmental conditions including concentration of population and industry etc. In small urban watersheds, there exists a high risk of inundation by river flooding and/or inner water induced by heavy rainfall in a short time. To estimate river water level accurately in urban small rivers, it is critically important to obtain accurate rainfall data with high resolution of spatio-temporal distribution. X-band MP radar (X-band multi-parameter radar), providing high resolution of spatio-temporal distribution rainfall data, is expected to be made effective use of its advanced detailed data. However, few studies on the precision evaluation of 1-minute X-band MP radar data were performed. In this study, a precision evaluation of X-band MP radar data was conducted by comparing radar data to 1-minute ground observation data, which is densely deployed in Tokyo Metropolitan area, provided by Tokyo Integrated Information System on Water Disaster Management. In this study, 10 heavy rainfall events in 2013 were selected as target events in the upper Kanda River, one of the typical urban small rivers in Tokyo. As for rainfall intensity, 1-minute data of X-band MP radar expressed a better peak accuracy compared with 10-minute data. The peak values of 10-minute data were underestimated about 30% in some event. One-minute data of X-band MP radar were observed a few minutes earlier than ground observation data. The falling time of rain drops is considered as the major factor of the difference. This study showed that it is possible to obtain detailed rainfall characteristics such as precise rainfall intensity and its time of occurrence by utilizing 1-minute X-band MP radar rainfall, which are not sufficiently provided by 10-minute data and its extended resolution is anticipated to be practically useful in smaller urban watersheds.
1-minute data, ground observation rainfall data, Kanda Riverm, small urban watershed, X-band MP radar, XRAIN
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