Global urban impacts of future climate extremes: Projections of heatwaves, droughts, and floods

Cities worldwide face increasing threats from Extreme Climate Change, as hazards such as heatwaves, droughts, and floods pose growing risks to urban populations and infrastructure. However, global regional assessments of exposure to extreme climate hazards under worst-case scenarios remain limited. This study presents a global assessment of regional exposure to heatwaves, droughts, and floods by the end of the century using upper-quartile projections from 20 CMIP6 climate models under the SSP5-8.5 emissions scenario. Changes in these hazards were evaluated individually and in combination across thousands of cities. Results indicate heatwave frequency will increase by over 90% in many tropical and coastal urban areas, and temperature extremes up to 12.7 °C above historical values will occur in high-latitude cities. Over 120 cities are projected to exceed critical wet-bulb temperature thresholds for human health. Drought severity is projected to intensify significantly in South America, Africa, and Southeast Asia, becoming up to 3.2 times more severe than historical extremes. Flood risks, measured by river discharge, are projected to increase substantially in South America and Asia, with increases up to 85 times historical levels. Compound hazard analysis further identifies significant overlapping exposure in cities across Africa, Southeast Asia, and South America. These findings highlight substantial regional exposure to extreme climate hazards and emphasise the urgent need for targeted urban adaptation and resilience planning worldwide.