Unveiling the dynamics of dry-and-humid, day-and-night, and compound heat waves across 209 Cities in China during 1974–2021

Abstract

Heatwaves (HWs) in China significantly impact human health and socioeconomic development, with these effects intensified by global warming and urbanization. This study provides an inter-comparison of the spatiotemporal variations and physical mechanisms of six HW types across 209 Chinese cities from 1974 to 2021: dry-daytime (DD), dry-nighttime (DN), dry-compound (DC), humid-daytime (HD), humid-nighttime (HN), and humid-compound (HC) HWs. We analyzed climatological data to assess the occurrence, duration, and intensity of each HW type, examining temperature anomalies, cloud cover, and atmospheric circulation patterns. We also evaluated the influence of climate change and urbanlization on HW dynamics. The findings demonstrated that DC and HC HWs exhibited longer duration and higher magnitude than other types across the China, 25.4 % of Central and Southwest cities transitioned to DC-dominant HWs (1974–2013), while 17.2 % of Northern and Western cities shifted to HC-dominant HWs (2014–2021). Furthermore, DC and HC are associated with larger spatial extent of positive temperature anomalies, negative total cloud cover anomalies, and stronger anomalous anticyclonic circulation compared to other HWs types. Additionally, both El Niño–Southern Oscillation and North Atlantic Oscillation were in positive phases, showing a synergistic correlation with increased durations of six HWs. In 1974–2013, DC and HC magnitude were increasing (0.15–0.35 /decade) at low- to very high- urbanization level; after 2014, HC/DD/DN/HN showed an increase (0.04 to 3.61 /decade) at low, moderate, and very high levels. HC (2.3 % at a moderate level) and HN (22.5 % at a very high level) had underscored the influence of urbanization on transfomation of HWs.