Unequal potential to mitigate future urban heat for cities in different climates

Rising heat risks, driven by increasing urban temperatures and growing populations, pose significant challenges for cities worldwide. However, the potential for mitigating these risks across different climate zones remains insufficiently explored. Here, we use physical-based numerical urban climate simulations to provide a robust assessment of the potential to reduce future urban heat risks around 2050 for 2000+ cities worldwide across climate zones. The Weather Research and Forecasting model coupled with the urban canopy model (WRF-UCM), driven by two CMIP6 future climate and urban expansion projections, was run for ten summers to evaluate the influence of global warming, urban expansion and climate uncertainties. We implement widely recognized urban heat mitigation measures, including urban greening, cool roofs and pavements, and enhanced air conditioning efficiency, in the numerical model. As a result, we found the cooling potential for wet-bulb global temperature  or humid heat stress is strongly influenced by background climate and geolocations. In temperate and sub-tropical climates, cities generally exhibit greater cooling potential, with mean  0.33 °C and 0.63 °C, for daytime and nighttime, respectively, compared to tropical cities where the mean  values are only 0.08 °C and 0.27 °C. For cities in dry climate (summer precipitation < 300 mm), the proposed mitigation measures can reduce humid heat by 0.48 °C, whereas in wet climates (summer precipitation > 300 mm), the reduction is limited to 0.20°C. These results demonstrate unequal potential to mitigate future urban heat for cities in different climates and highlight the urgent need for heat mitigation innovations and climate mitigation actions, especially for tropical cities threatened by humid heat.