Impacts of Continuously Increasing Urbanization Ratios on Warming Rates and Temperature Extremes Observed Over the Beijing Area

Abstract

AbstractEvaluations of the impacts of increasing urbanization ratios on air temperatures are less quantitative and accurate due to the lack of high‐resolution land cover data sets. Here, based on the latest released high‐resolution (30‐m) land cover data from 1985 to 2017, annual urbanization ratios around each station in Beijing were calculated. Warming rates and temperature extremes were compared between nonrural stations (17 stations with continuously increasing urbanization ratios) and purely rural stations (3 stations with continuous urbanization ratios of zero). Although urbanized areas only occupied 22.2% of the total area in Beijing, urbanization ratios at nonrural stations already reached an average of 62.4% (10 km2)−1in 2017, and their average rate reached 15.1% (10 km2)−1 decade−1. From 1985 to 2017, each 10% increase in the urbanization ratio with 10 km2had led to additional annual warming of 0.14 ± 0.11, 0.17 ± 0.08, and 0.30 ± 0.17°C at nonrural stations for daily maximum (Tmax), mean (Tmean), and minimum (Tmin) air temperatures, respectively. Meanwhile, each 10% increase in the urbanization ratio with 10 km2had led to additional changes of 11.6 ± 5.1, 12.7 ± 5.8, and −11.1 ± 5.2 days at nonrural stations for hot days, hot nights, and chilly nights, respectively. Additionally, the inner‐annual urbanization contributions to the warming increased significantly at rates of 10.7% decade−1and 14.1% decade−1forTmeanandTmin, and reached 49.0% and 52.6% in 2017, respectively. The inner‐annual urbanization contributions to the increasing hot nights and the decreasing chilly nights changed at rates of 16.7% decade−1and 15.6% decade−1, and reached 57.8% and 53.1% in 2017, respectively.