Urban heat islands in China enhanced by haze pollution

TLDR

Urban heat islands arise from biophysical changes in urban land surfaces. The study tests whether urban aerosol or haze pollution also contributes to the UHI. Satellite observations and urban climate model calculations were used to assess this effect. Nighttime UHI across China is significantly driven by urban–rural haze differences, adding an average of 0.7 ± 0.3 K, with a stronger impact in semi‑arid cities, indicating that haze mitigation can reduce urban heat stress.

Abstract

Abstract The urban heat island (UHI), the phenomenon of higher temperatures in urban land than the surrounding rural land, is commonly attributed to changes in biophysical properties of the land surface associated with urbanization. Here we provide evidence for a long-held hypothesis that the biogeochemical effect of urban aerosol or haze pollution is also a contributor to the UHI. Our results are based on satellite observations and urban climate model calculations. We find that a significant factor controlling the nighttime surface UHI across China is the urban–rural difference in the haze pollution level. The average haze contribution to the nighttime surface UHI is 0.7±0.3 K (mean±1 s.e.) for semi-arid cities, which is stronger than that in the humid climate due to a stronger longwave radiative forcing of coarser aerosols. Mitigation of haze pollution therefore provides a co-benefit of reducing heat stress on urban residents.