Climate and land-use drivers of future flood exposure and damage in the Cagayan River Basin, Philippines

Study region. The Cagayan Valley Region (Region II) in northern Luzon, Philippines, includes the Cagayan River Basin, the country’s longest river system and largest catchment. The basin is a major rice- and corn-producing area, but recurrent tropical-cyclone and monsoon floods cause damage almost every year. Study focus. This study assesses future flood hazard, exposure, and private-sector damage by integrating climate, land-use, and population scenarios within a common time frame. Climate forcing came from three CMIP6 GCMs – ACCESS-CM2, CanESM5, and EC-Earth3-Veg-LR – under four SSPs, and bias-corrected rainfall drove the RRI model. Future land use was projected by combining Land Change Modeler susceptibility scores with population- and crop-area demand constraints, while population distribution was estimated from government projections and spatial covariates. By overlaying projected land use, population, and inundation, the study quantifies crop-specific exposure, separates climate- and land-use-driven contributions, and evaluates land-use regulation. New hydrological insights. This integrated assessment shows that simulated peak discharge increases across all future SSP scenarios because rainfall events exhibit higher short-duration intensity and sharper temporal peaks. The 100-year inundated area increases by more than 31% under higher-forcing scenarios. Under the medium population scenario, exposed population increases by about 100%, from approximately 1 million at present to 2 million by 2070. Climate change mainly increases frequent-flood exposure, whereas land-use expansion amplifies rare-flood exposure and damage. Risk-informed land-use regulation reduces future housing losses by up to 154 million PHP yr −1 .