Concurrent droughts and heatwaves, known as compound hot-dry events (CHDEs), have been increasing globally in recent decades. The increasing frequency and intensity of CHDEs pose significant risks to crop yield, water resources, and ecosystem services. In the summer of 2022, simultaneous drought and heatwave emerged in many regions of China, especially the Yangtze River Basin (YZB). Approximately 360 million people experienced temperatures exceeding 40 °C at some point during this summer in China. Moreover, the extremely hot and dry conditions brought serious threats to the national electric system and water security, cascaded into other hazards including wildfires and crop yield losses, and caused numerous heat-related deaths.
In this study, Associate Prof. Bo Qiu and Prof. Weidong Guo’s group investigated the role of land-atmosphere feedback in the development of this CHDE using reanalysis data and soil moisture-temperature coupling index. In summer 2022, long-lasting temperature extremes continuously consumed soil water, leading to substantial water loss . Then, large amounts of surface net radiation were partitioned to sensible heat instead of latent heat as the soil moisture-temperature coupling pattern shifted from energy-limited to water-limited under low soil moisture conditions, forming positive land–atmosphere feedback and leading to unprecedented hot extremes in August. The distribution of extremely high temperatures in YZB exhibited significant spatial heterogeneity, which was largely modulated by the land–atmosphere coupling strength. Furthermore, changes in the frequency and intensity of CHDEs in the YZB over the past 40 years were closely linked to changes in the local land–atmosphere coupling strength. This study improves the understanding of the development of CHDEs from the perspective of land-atmosphere interaction, reveals the influence of land–atmosphere coupling strength on the timing, intensity, and spatial distribution of CHDEs, and enables more effective early warning of CHDEs.
This study is published in Environmental Research Letters, entitled “Shift of soil moisture-temperature coupling exacerbated 2022 compound hot-dry event in eastern China”. Graduate student Yueyang Ni is the first author, Associate Professor Bo Qiu and Professor Guo Weidong are the corresponding authors. Other co-authors include Dr. Xin Miao, doctoral student Lingfeng Li and Jiuyi Chen. This research is jointly supported by the Frontiers Science Center for Critical Earth Material Cycling of Nanjing University, the Fundamental Research Funds for the Central Universities (14380191, 14380172), the National Natural Science Foundation of China (42175136 , 42305033), and Jiangsu Collaborative Innovation Center for Climate Change.
Reference:
Ni, Y., Qiu, B., Guo, W. et al. (2024). Shift of soil moisture-temperature coupling exacerbated 2022 compound hot-dry event in eastern China. Environmental Research Letters. https://doi.org/10.1088/1748-9326/ad178c
Figures (a)-(f) show three-day-averaged YZB-mean anomalies of soil moisture and net radiation versus (a, b) temperature, (c, d) surface sensible heat flux, and (e, f) surface latent heat flux from July 28 to August 20 in 1982–2022 (8 dots per year). Figure (g) shows the evolution of the YZB-mean standard deviations of the five variables throughout July and August.