Variations in summertime compound heat extremes and their connections to urbanization in China during 1980–2020

Abstract

Summertime heat extremes are exceptionally harmful and destructive to human health and socio-economic systems. Based on 2419 meteorological stations, this study investigates the temporal and spatial characteristics of summertime extreme high temperatures across China and their response to urbanization over the period 1980–2020. The results show that (a) both the maximum temperature (TXx) and minimum temperature (TNn) in the summer have shown an upward trend in most parts of China during the past 40 years; significant upward trends are found in eastern China for independent hot days (IHDs), independent hot nights (IHNs) and compound hot events (CHE). (b) Extreme heat shows a positive spatial clustering pattern across China. The hot spots of the three compound heat events (including IHD, IHN and CHE) are mainly distributed in the north; while the cold spots are roughly distributed in the south. The spatial pattern of hot and cold spots of TXx exhibits an east-west orientation while that of TNn shows a southeast-northwest orientation. (c) The correlation between the heat extremes and urbanization level varies among regions, with most exhibiting linear and exponential relationships. Significant urbanization effects on TXx and TNn are detected in all sub-regions, with contributions ranging from 11% to 41% and 14% to 29%, respectively, while urbanization contributions to the three compound heat events vary significantly among the sub-regions. Our findings present the spatio–temporal patterns of summertime heat extremes, especially the spatial clustering pattern of the compound extremes, and thus enrich the understanding of these variations and their regional response to urbanization, which may have important implications for policy-making among distinct sub-regions.