EVALUATION OF FLASH FLOOD SUSCEPTIBILITY IN RELATION TO LAND USE CHANGES IN CHIANG RAI, THAILAND

Abstract

Flash floods are among the most destructive natural hazards in mountainous regions, characterized by their rapid onset and severe impact on lives and infrastructure. This study assessed the spatio-temporal evolution of flash flood susceptibility in Chiang Rai Province, Thailand, by integrating remote sensing, Geographic Information Systems (GIS), and hydrological modeling. Using the Flash Flood Potential Index (FFPI), the study analyzed the impact of land use and land cover (LULC) changes on flood risk across three distinct periods: 2007, 2012, and 2018. The model incorporated terrain slope, soil hydrological groups (derived from HYSOGs-250m), land use, and Curve Number (CN) values to generate comprehensive risk susceptibility maps. The results revealed that the entire province falls within Moderate to High-risk categories, with a complete absence of Low-risk zones. A significant shift in susceptibility was observed over the study period, driven primarily by land-use transitions. While the conversion of woodland to agriculture moderately elevated risk levels between 2007 and 2012, the subsequent rapid urbanization of agricultural lands (2012–2018) led to a drastic escalation in vulnerability. Notably, high-risk zones within urban areas increased fivefold (+500%) during this latter period. The FFPI model was validated based on the historical flash flood records from 2019 to 2023, demonstrating a strong spatial correlation between analyzed high-risk areas and actual flash flood occurrences. These findings underscored that anthropogenic land-use changes, particularly uncontrolled urbanization and deforestation, are the primary accelerators of flash flood potential, necessitating rigorous land-use planning and targeted flood-control infrastructure.