TRMM Rainfall Estimates and Typhoon Rainfall Risk in the Western North Pacific Basin

Freshwater and storm surge flooding often devastate many countries in the Western North Pacific (WNP) basin each typhoon season with economic damages amounting to billions of US Dollars. Although storm surge is one of the main causes of coastal and inland flooding due to landfalling tropical cyclones (TCs), in many cases heavy rainfall also contributes to flooding and often land/mud slides. For assessing the impact of TCs on lives and properties, one has to therefore properly quantify TC flood risk from the rainfall. The quantification of TC flood hazard is therefore highly related to the quality and completeness of TC best-track data. In this study basin-wide TC best track data for the Western North Pacific basin is used to create a relatively complete best-track data set by supplementing the Joint Typhoon Warning Center (JTWC) best-track data with data from multiple sources. TC best-track data from the JTWC, Japan Meteorological Association (JMA), and Shanghai Typhoon Institute of the China Meteorological Administration (STI-CMA) are analyzed to create a best-track data set more complete amongst all the data sets in space and time for the period 1945-2014. The supplemented best-track data set created is relatively complete over land and over the northwestern Pacific Ocean off the coast of northeast Japan where the original JTWC data is incomplete. Using the original and supplemented JTWC best-track data the study aims to differentiate TC generated rainfall totals and fresh water flood risk when TCs make landfall in the WNP basin. The total rainfall accumulated for each TC track during the 1998-2014 TC seasons is calculated using the 3-hourly Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) data. In general the TC annual average rainfall (AAR) estimated using the supplemented best-track data is 30% to 40% higher along coastal and inland China, Vietnam, and Thailand than the AAR from the original JTWC best-track data. In Japan the AAR estimated using the supplemented best-track is about 20% to 30% higher than the AAR from the original JTWC data. The impact of this difference in TC accumulated rainfall is estimated using a basin-wide typhoon risk model.