Climate-driven spatiotemporal dynamics and exposure risks of global soil moisture drought–flood abrupt alternation events

Drought–flood abrupt alternation (DFAA) events, characterized by rapid transitions between drought and flood conditions, pose severe challenges to agricultural production, water resource management, and infrastructure systems. While previous studies have characterized such events predominantly using precipitation, runoff, or composite indices, soil moisture–driven DFAA (SMDFAA) remains understudied, despite its critical role in regulating land–atmosphere interactions and surface hydrological stress. Here, we develop a novel daily-scale framework to detect SMDFAA events and track their historical trends since 1983. We further assess their projected future trajectories under four Shared Socioeconomic Pathway (SSP) climate scenarios and quantify national-scale exposure risks. Cross-dataset assessments demonstrate high consistency in identifying SMDFAA hotspots in regions including the Central United States, southern South America, the Mediterranean, South Asia, and eastern Australia. Drought-to-flood (DTF) transitions are consistently more frequent than flood-to-drought (FTD) globally. Under the high-emission SSP5-8.5 scenario, global root-zone DTF and FTD frequencies are projected to increase by approximately 7.59% and 19.64%, respectively, by the end of the 21st century relative to the 1985–2014 baseline. DTF intensification is particularly pronounced across regions outside western central Asia, northern North America, northern South America, and central Africa, while FTD increases are most marked in high-latitude regions. Globally, 93 to 129 countries are projected to experience elevated SMDFAA exposure risk by 2071–2100. These findings underscore intensifying compound soil moisture extremes under climate change, providing a critical evidence base for informing adaptive water management and climate-resilient risk mitigation.