On the possibility of the 2022-like spatio-temporally compounding event across the Yangtze River Valley

During July-September 2022, heatwaves, droughts, forest fires and floods hit the Yangtze River Valley (YRV) successively, constituting a spatio-temporally compounding event. Starting in mid-July, one of the most severe, sustained and extensive hot-drought took place over much of the YRV, leading to power outages and harvest failures in the electricity- and water-rich region. The hot-dry weather dried out forests, and sparked numerous wildfires. The hazard chain extended as some of the burned areas received heavy precipitation, where the flood and debris flow risks stayed high in the following months. The rapid sequencing of multiple extremes shortens relief windows, enhances exposure/vulnerability of natural and human systems to the next hazard(s), and therefore overwhelms their ability to respond. Understanding its risks matters to disaster preparedness.       The single-model initial-condition large ensembles (SMILEs) offer a broad range of physically plausible climates that better serve for exploring the possibility of extremes at a given warming level. To this end, we address the event possibility issue in the SMILEs framework. Through searching for event analogues in SMILEs, we report that the 2022 unprecedentedly widespread and intense hot drought might have occurred as early as in the 1970s, and would become increasingly possible and spatially extensive with warming. This tendency is also supported by the conventional multi-model (CMIP6) projection, especially evident in larger ensembles. Lower reaches of the valley and parts of Southwest China have greater chances of repeated exposure to the 2022-like heat—drought—fire—flood quadruple compound events. In the context of favorable internal variability in line with future warming, it is plausible to see more than half of the valley at simultaneous risk of similar quadruple compound events. Our possibility projections highlight the urgency of accelerating the existing univariate extremes—oriented adaptation measures to address emerging threats from unfamiliar compound hazards.