Increasing exposure to potential flooding in high-mountain catchments

Abstract Exposure to flood hazards in high mountain catchments is expected to increase alongside natural hazards, driven by climate change, glacier retreat, and landscape evolution, yet temporally consistent, high-resolution exposure data remain scarce. Here we quantify changes in the exposure of buildings and people to flooding in Nepal and transboundary regions of India and China. Validation against a manually derived reference dataset revealed considerable differences in accuracy and completeness across five building footprint products. Google Open Buildings Temporal 2.5D (OBT) displayed the highest median accuracy (F1 = 0.68), followed by Google Open Buildings V3 (F1 = 0.62). We assessed exposure relative to river channels using the height above nearest drainage (HAND) metric and modelled glacial lake outburst flood (GLOF) inundation extents. Building area within 0–50 m vertical proximity to channels increased by 46% between 2016 and 2023, while those located within modelled GLOF extents increased by 77%. Population projections indicate continued growth in areas of potential flood exposure, with 18% ( n = 293,800) of the study-area catchment population estimated to reside within 0–50 m HAND in 2026. Our results demonstrate rapidly increasing exposure in Himalayan catchments and highlight the importance of validated, multi-temporal exposure datasets to inform disaster risk reduction.