Assessment and pre-assessment of compound hot and drought events over Yangtze River Basin

The severe compound hot and drought event (CHDE) in 2022 had serious impacts on water resources, agriculture, power supply, and ecosystems in the Yangtze River Basin (YRB). In this paper, we asked, have similar spatiotemporally overlapping compound events, like the one observed in 2022, occurred historically in the basin? And, if so, how can we pre-assess the impacts of such potential events on subseasonal timescales? To address these questions, regional CHDEs in the YRB since 1961 were systematically identified and comprehensively assessed using a modified intensity-area-duration technique and hazard assessment methods. Additionally, the subseasonal pre-assessment capability for CHDEs in the YRB using the China Meteorological Administration's third-generation climate model prediction system (CPSv3-S2S) was demonstrated. A total of 140 CHDEs occurred during 1961-2022, with the 21st century showing a remarkably high risk of such events. Among these, 2022 was the most intense year, with the event from July 26th to August 30th being unprecedented in severity. CPSv3-S2S effectively forecast this event's occurrence within a 1-25 lead days, particularly in pre-assessing its extensively impacted area and high-hazard centers in the upper and middle reaches of the main river course. This pre-assessment method serves as a valuable reference in decision-making to anticipate and mitigate the risks of hydropower supply shortages and heightened electricity demand during extremely high temperatures in upstream areas.