Elucidating the Varied Characteristics of Compound Hot–Drought From Two Distinctive Extreme Events in the Yangtze River Valley

Abstract

Compound hot-drought events exert profound impacts on ecosystems, agriculture and public health, highlighting the need to understand their characteristics and driving mechanisms for effective climate change mitigation and adaptation strategies. This study reveals that the severity of summer hot–drought events in the Yangtze River Valley (YRV) significantly increased during 1961–2022. Among these, 2013 and 2022 represent two distinct types of hot-drought events: High-temperature and both high-temperature and deficient precipitation dominated. In both years, the eastward expansion of the South Asian High and the westward extension of the Western Pacific Subtropical High established persistent high-pressure systems over the YRV. In 2013, cooler sea surface temperature (SST) anomalies in the Northwestern Indian Ocean promoted the anomalous westerly, reducing the southwest water vapour transport to the region. Concurrently, the Western North Pacific anticyclone (WNPAC) positioned over the East China Sea facilitated limited moisture inflow from the Pacific. This configuration, mainly governed by persistent high-pressure systems, resulted in high-temperature-dominated compound events. In contrast, the 2022 event displayed greater complexity. Warmer SST anomalies in the Bay of Bengal intensified convective activity, enhancing the local Hadley circulation and promoting descending motion over the YRV. Strengthened easterly, influenced by the Matsuno–Gill response, contributed to the westward extension of the WNPAC and altered tropical water vapour transport, causing pronounced tropospheric descent and moisture deficits over the YRV. Negative tropospheric potential vorticity anomalies further exacerbated the compound event through land-atmosphere interactions, including scarce precipitation, soil drying and increased surface sensible heat flux. Consequently, the 2022 event was more severe and multifaceted than that in 2013.