Long-term flood exposure assessment using satellite-based land use change detection and inundation simulation: A 30-year case study of the Bangkok Metropolitan Region

The Bangkok Metropolitan Region (BMR), located in the Chao Phraya River basin delta, is particularly vulnerable to floods, with susceptibility heightened by geographical aspects and rapid urbanization. This study aimed to assess spatiotemporal flood exposure and allow proper flood-risk recognition among all stakeholders through a three-phase flood exposure assessment. First, land use and land cover (LULC) changes were identified based on a 30-year Landsat time series. Second, built-up areas that overlapped with past flood inundation maps were designated as flood exposure areas. Third, a rainfall-runoff inundation (RRI) model simulated the 2011 Thailand Flood, the largest on record, by analyzing inundation depth implications across three decades. The findings revealed a dramatic increase in the use of built-up areas and the associated flood exposure. In 1992, built-up areas accounted for approximately 20% of the total area, sharply increasing to nearly 45% by 2022, according to the LULC classification. The flood exposure increased from 648.83 km² in 1992 to 1681.26 km² by 2022, demonstrating a linear trend. Notably, the catastrophic 2011 flood did not inhibit urbanization in flood-prone areas, highlighting the need for robust policies, such as the segmentation of flood-risk zones, to mitigate future exposure in the region.