Assessing the consequences of compound coastal–fluvial flooding under climate change: exposure, vulnerability and damage estimates in eastern England

Flood risk is projected to increase under climate change due to more frequent extreme events and expanding human development in hazard-prone areas. While large-scale assessments provide valuable overviews of emerging risk, they often lack the spatial detail and social-environmental integration needed to inform local adaptation planning. This study applies a high-resolution hazard-exposure-vulnerability framework to assess compound coastal–fluvial flood risk and evaluates how methodological choices affect estimates of exposure, economic damage and spatial risk. The framework is applied to the low-lying Broadland catchment in eastern England using UKCP18 convection-permitting climate projections under RCP8.5 to simulate compound flood scenarios for 1990, 2030, and 2070. Exposure is assessed using population and property data, while vulnerability is quantified across 31 social, economic, and environmental indicators statistically weighted via principal components analysis. The results show that methodological choices can substantially influence outcomes. In particular, building depth sampling methods and depth–damage assumptions can alter loss estimates by over 70%, while different population datasets affect estimated human exposure. By using the OpenPopGrid population dataset and the footprint-maximum depth, the estimated economic damages increase from £439 million in 1990 to £718 million in 2070, with risk concentrated in urban coastal locations where exposure and vulnerability converge. By integrating high-resolution climate projections with spatially explicit vulnerability analysis, this study demonstrates how local-scale assessments can provide spatially detailed evidence to inform adaptation planning. The framework is potentially transferable to other coastal and estuarine regions, although its implementation depends on the availability and local suitability of hazard, exposure and vulnerability data.