Climate change overrides population dynamics in driving flood exposure in the Yangtze River Basin

Yangtze River Basin River floods expose large populations to life-threatening conditions, yet the joint influence of climate change and socioeconomic development on future flood exposure in the Yangtze River Basin remains poorly quantified. Here we assess population exposure to river floods by coupling the distributed hydrological model WEB-DHM-SG with Inter-Sectoral Impact Model Intercomparison Project phase 3b bias-correct climate projections under multiple Shared Socioeconomic Pathways. Exposure is evaluated for historical, near-future (2036–2065) and far-future (2071–2100) periods under SSP126, SSP370 and SSP585, as well as for global warming levels from 1.5 to 4.5 °C. We found that basin-wide exposure increases from about 30 million historically to roughly 50 million in the near-future across all scenarios, and remains about 35–40% above historical under SSP126 and SSP585 but nearly doubles under SSP370 by late century. High-exposure and strongly increasing sub-basins are consistently concentrated in middle- and lower-reach floodplains, whereas many upper-reach sub-basins show decreasing exposure, reinforcing existing upstream–downstream inequalities. Warming-level and decomposition analyses indicate that climate change shifts the basin from a low- to a high-exposure regime, while population dynamics mainly modulate exposure at low warming levels and play a minor or compensating role thereafter. These results highlight the middle and lower Yangtze as priority regions where spatially targeted adaptation and risk-informed development will be essential to limit future flood risk. • Climate change drives a shift to high flood exposure in the Yangtze River Basin. • SSP370 yields persistent, amplifying flood exposure hotspots in downstream areas. • A robust upstream-downstream contrast in flood exposure emerges across all scenarios. • Population dynamics modulate risk at low warming levels but diminish at higher levels. • Exposure jumps markedly at 1.5 °C warming but plateaus at higher temperatures.