Urban expansion weakens the contribution of local land cover to urban warming

Abstract

Previous studies have shown that changes in local land cover can significantly influence air temperature. What remains unaddressed is whether, and at which point, such within-city changes would become insignificant with cities continuing to expand. Here, we identify annual urban expansion and local land cover change in Beijing from 1985 to 2018, using time-series data of impervious surfaces. We further examine their impacts on temperature using multiple linear models. We found urban expansion and local land cover change jointly affected urban warming, but their relative contribution changed over time, showing the occurrence of three turning points. The first one occurred at the city size of 976 km2, before which the local land cover change was the predominant factor contributing to urban warming. Both factors significantly affected the mean temperature with city size growing from 976 km2 to 2272 km2, showing the relative importance of the local factor decreased, while the relative importance of the city-scale factor continued to increase, and became greater when the city was larger than 1646 km2. The local factor did not play any significant role when the city area exceeded 2272 km2. Results can provide insights on urban planning for heat mitigation and adaptation.