Characteristics of Boreal Summer Compound Hot-Drought Events in the Yangtze River Valley and Relationships with Indian Ocean Sea Surface Temperature

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Abstract

Compound hot-drought events (CHDEs) have drawn widespread attention for their severe impacts on ecosystems and human livelihoods. This study investigated the characteristics and driving mechanisms of boreal summer CHDEs in the Yangtze River Valley (YRV) during 1961–2022. Results showed that the most intense events were concentrated in Sichuan Province, with both the affected area and event severity exhibiting significant upward trends during the study period. A strong relationship was identified between CHDEs in the YRV and sea surface temperature (SST) anomalies in the Indian Ocean, independent of El Niño-Southern Oscillation (ENSO) influences. Cold SST anomalies cooled the tropical troposphere, triggering easterly winds over East Asia subtropical regions. Concurrently, increased precipitation over north-central India induced an upper-tropospheric anticyclone over the northwestern Tibetan Plateau. In turn, the propagated Rossby waves promoted anticyclonic conditions over East Asia and maintained a meridional dipole circulation pattern. Anomalous high-pressure systems over the North Atlantic and Europe-West Siberia amplified these patterns, which further altered surface radiation budgets, drying the land and enhancing sensible heat flux. The resulting land-atmosphere interaction sustained anticyclonic circulation, intensifying CHDEs in the YRV. Projections under the high-emission SSP5-8.5 scenario suggested that the frequency of these atmospheric circulation patterns was likely to increase, exacerbating CHDEs in the YRV and posing heightened risks to the environment and society.

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