Analysis of 3-D unprecedented torrential and convective rainfall by high resolution X band radar precipitation

Cho Nyunt, Yoshihisa Kawahara, Ryota Tsubaki, Boris Kolar

Wednesday 1 july 2015

9:30 - 9:45h at North America (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Early warning systems

Parallel session: 8I. Extreme events - Flood Drought

Record-breaking torrential heavy rain surpassed its average of the whole month within three hours in the western Japan on 25 August, 2013 and the sudden localized downpour showed over 200 mm within the first three hours during the early morning of 20 August, 2014 in Hiroshima. Both unprecedented rains caused the flash flood, deadly landslides and damaged a lot of property and transportation facilities. Therefore, improving Quantitative Precipitation Estimates (QPE) by using a dense radar network with high temporal and spatial resolution is also a key component to mitigate the disaster evacuation. Moreover, this study is the preliminary study of high accuracy Quantitative Precipitation Forecast (QPF) using the Multiparameter radar at the X-band wavelength (MP-X radar) data assimilation coupling the Weather Research and Forecasting (WRF) model. The detailed analysis of the high temporal (1 min) and spatial resolution (250 m) 2D MP-X radar near surface rain and 3D mosaic rain gridded with 250 m in the vertical direction and 500 m in the horizontal direction is very important to use as the updated initial condition to couple with WRF. The analysis area covers the two radars named Ushioyama and Nogaibara in the western Japan. The pros and cons of X-band radar rainfall are compared to the rainfall observed by Radar- AMeDAS data which show 30 minute interval with 1 km resolution over the Japan. Moreover, 10 minutes accumulated rain by MP-X radar shows good agreement with the surface rain gauge when rain is less than 100 mm per hour and tend to underestimate over 100 mm due to the signal extinction area by the radar attenuation effect. But the accurate location and specific structures of heavy rain can be observed only by using 3D mosaic rain of MP-X radar with continuous time series analysis. This study investigated the two cases of rain events, torrential and convective rain, by using 2D and 3D mosaic rain for providing high-spatial and high-temporal MP-X radar rain to the implementation of high accuracy and short range QPF for early warning of disaster evacuation.