Enhancement of Global Flood Risk Due To Greater Flood Magnitude and Variability Under Anthropogenic Activities

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Abstract
Anthropogenic activities, including anthropogenic climate change (ACC) and historical water and land management (HWLM), have intensified hydrological extremes in recent decades, with potential increases in flood risk. However, uncertainties in hydrological models and a lack of consideration for HWLM in climate models have limited the estimation and attribution of the changes in global‐scale flood risks. Based on a multi‐model ensemble of daily discharge simulations and projections from the latest Inter‐Sectoral Impact Model Intercomparison Project (ISIMIP 3), our estimation shows that flood risks significantly increased (slightly decreased) in the north (south) of 50°N during 1971–2019 when considering the combined effects of ACC and HWLM. Under continuing global warming (from 1.5°C to 3°C), 59.6%–69.4% of the global land area would witness an increasing flood risk, with 71.9%–87.5% of basin‐level risks attributable to anthropogenic activities, particularly in arid/tropical zones. Meanwhile, the flood risk in 38.8% of the global land area shows the anthropogenic signals before 2065. This increase is enlarged by greater flood magnitude and variability in the future, with flood magnitude being the dominant factor in most regions. We suggest that hydrological services and policymakers should implement adaptive strategies that consider anthropogenic increases in flood magnitude and variability, utilizing detected signals to guide global flood‐risk mitigation.

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