HIGH-RESOLUTION SURFACE WATER MAP OVER JAPAN AND ESTIMATION OF INUNDATION AREA CAUSED BY TYPHOON HAGIBIS

Abstract

 We have developed a method to estimate inundation ratio by microwave radiometers, and to downscale it into 15-second grid with the help of geospatial dataset in Japan. In this study, this method is applied to all land area in Japan (excluding some remote islands), then high-resolution surface water map (GSMaWS) is produced. GSMaWS is compared with simulated inundation area by Today’s Earth-Japan (TEJ) and it is found that GSMaWS tends to overestimate inundation ratio in urban area, in Hokkaido, and along the coast, but GSMaWS and TEJ show positive temporal correlation in many river basins in eastern part of Japan in October 2019. For the flood event caused by Typhoon Hagibis, inundation area estimated by GSMaWS and TEJ are evaluated with the reference of inundation map published by Geospatial Information Authority of Japan. Just after the peak of heavy rainfall, in early morning of October 13, GSMaWS shows similar estimates of inundation area with TEJ, while the accuracy becomes worse during heavy precipitation.