Quantifying the impact of infrastructure-based urban adaptation strategies on summer air temperature and heat exposure risk in Chinese cities

Infrastructure-based heat reduction strategies, such as using cool building materials (high albedo) and street greenery, can be effective methods for cooling cities. However, the effectiveness of different measures on near-surface air temperature and population heat exposure in cities remains unclear. This study used the Weather Research and Forecasting model coupled with the single-layer urban canopy model and conducted one control and four urban adaptation strategy simulations (cool roof, green roof, urban tree and full adaptation) with a convection-permitting scale of 3 km in eastern China during the warm season of 2022. Our findings reveal that these strategies notably decreased 2 m air temperature, with averaged cooling effects of daily air temperature in 37 cities reaching −0.4 °C (cool roof), −0.3 °C (green roof), −0.2 °C (urban tree) and −0.6 °C (full adaptation). The cooling effects in cities illustrated notable regional characteristics; that is, they were stronger in Central China, East China, South China and North China but weaker in Southwest, Northwest and Northeast. Based on the results of multiple linear regression, we attributed the dominant climate factor of each measure: Bowen ratio for cool roof and urban tree and full adaptation and downward shortwave flux for green roof. In addition, urban adaptation strategies greatly reduced extreme heat hours in 37 cities, with averages of 67 (cool roof), 47 (green roof), 22 (urban tree) and 88 h (full adaptation). Furthermore, urban adaptation strategies substantially reduced population heat exposure in populated cities, such as Shanghai (2.48 billion person-h), Guangzhou (1.48 billion person-h), Beijing (1.26 billion person-h) and Shenzhen (1.17 billion person-h). In summary, urban cooling measures can notably decrease air temperature and reduce heat exposure risk during the warm season in cities but vary in their effectiveness in various cities, which highlights the need for region-specific approaches for adaptation to climate change.