Flash Flood Susceptibility Mapping in Phuket Province, Thailand: An Integrated Geo-Information Technology and Logistic Regression Approach

In the past 2 years, Phuket has experienced more frequent flash floods, resulting in significant damage to life and property for the people of Phuket. This research aimed to assess flash flood susceptibility using Geo-information technology (GIS) and logistic regression analysis in Phuket Province. The statistical results from the logistic regression analysis were subsequently processed using the geographically weighted regression method within GIS. The results of the study found that the factors with the most influence on flash flood occurrence were Topographic wetness index (TWI), Stream frequency (SF), Drainage density (DD), Infiltration number (IN), Slope, Distance to road, Mean annual precipitation, Elevation, Land use, Sediment transport index (STI), Stream power index (SPI), Distance to stream, and Geology, respectively. All these variables are shown from the exp β value coefficient, when compiled into a flash flood susceptibility map, it was found that very high flash flood susceptibility level covers an area of up to 43.40 km2 (8.04% of the total area). Most of it covers the areas along the major rivers of Phuket Island. The most obvious is the mountainous terrain with rivers flowing through it, the piedmont and intermontane plains in the northern part of Phuket, which is the Thalang District and Kathu Sub-district. The coastal plain landscape of the eastern part of Phuket Island also shows areas of very high flash flood susceptibility level scattered along major waterways in the Ko Kaew, Talat Yai, Talat Nuea, Wichit, Chalong, and Rawai sub-districts. However, the top three variables influencing flash flood occurrences in Phuket were the TWI, SF, and DD. This highlights the high susceptibility of the study area's coastal foothill regions to flash flooding, primarily due to their function as a confluence point for multiple stream branches. The findings of this research indicate that the TWI, SF, and DD are significant variables contributing to flash flood occurrences in terrains characterized by narrow coastal plains adjacent to major mountain ranges. The results of this research are to creat a flash flood risk map, intended to inform and enhance upcoming flood monitoring strategies.