Impact analysis of ISO signals on the compound High-Temperature and Drought disaster event in Southwest China during August–September 2024

From mid-August to mid-September 2024, a typical compound high-temperature and drought disaster occurred in Southwest China, significantly impacting local economies and people"s livelihoods. While such compound disasters in this region have been linked to intraseasonal oscillations (ISOs) originating from various areas, conventional statistical analyses fail to distinguish the specific roles of different ISOs in driving these events. This study employs ISO signal-driven WRF lateral boundary forcing numerical simulations and reveals: The ISO signal triggered by mid-latitude westerly belt wave trains in the upper troposphere predominantly influenced the northern part of Southwest China, elevating regional temperatures by 1.10°C on average and exacerbating drought conditions in the Sichuan Basin and its northern areas. The ISO signal associated with teleconnection wave trains in the lower troposphere exerted more pronounced impacts on the entire region, driving an average temperature increase of 1.93°C. During the early stage of disaster development, the region was primarily affected by mid-latitude westerly belt wave trains from the northern boundary, with negative vorticity transport gradually establishing subsidence conditions conducive to temperature escalation. In the mid-late phase, warm advection induced by the westward extension and northward shift of the western Pacific subtropical high, coupled with positive anomalies in tropospheric geopotential height fields, collectively drove regional temperature increases and soil moisture depletion. These findings enhance understanding of the mechanisms behind compound high-temperature-drought disasters and provide foundational insights for their subseasonal prediction.