When extreme heat and drought coincide as concurrent hot and dry events, their combined impact far exceeds the damage caused by heatwaves or droughts on their own — triggering widespread crop failures, depleting freshwater reserves, escalating wildfire risk, and raising mortality risks tied to heat and dehydration. Most prior research on these compound extremes has focused on tracking how often they occur nationwide, but few studies have systematically unpacked the physical drivers behind their growing severity. A new study led by Professor Qin Su’s team at Yunnan University addresses that gap — and finds that identical-looking worsening conditions in different parts of China are being driven by very different mechanisms.

Published in Atmospheric and Oceanic Science Letters, the study confirms pervasive intensification of summer concurrent hot and dry events across China and reveals that this worsening stems from vastly different physical driving mechanisms depending on region. The team systematically investigated the separate physical mechanisms behind intensifying trends in the two major high-risk zones: western China and east-central China.

Two Regions, Two Very Different Stories

“For decades, researchers treated national CHDE trends as a uniform response to global warming, but our 40-year dataset proves this is misleading,” says corresponding author Prof. Qin Su. “Western China’s risk surge is driven purely by anthropogenic warming, while east-central China’s hazards stem from coupled monsoon decline, drought amplification, and heat feedback. Distinguishing these regional disparities is mandatory for precise climate risk mapping and tailored local climate adaptation plans.”

The study also turned up a striking supplementary finding: the areas seeing the fastest growth in intensity are predominantly situated on the leeward sides of large topographic features. That pattern can be explained by adiabatic atmospheric processes — air masses release precipitation as they ascend windward mountain slopes, leaving the air depleted of moisture. After crossing mountain crests, the descending air undergoes adiabatic compression, which rapidly raises its temperature and generates hot, dry air on the leeward side. Under global warming, these already dry and hot baseline environments further amplify the increasing trend of heat and drought severity, making leeward regions especially vulnerable to increasingly severe compound extremes.

“Topography cannot be ignored when projecting future hot-dry hazards, especially for mountainous and foothill regions,” Su notes. The findings, the researchers say, provide a solid theoretical foundation for developing early prediction and warning technologies for these compound events, and offer critical scientific support for refined climate risk governance as well as targeted regional disaster prevention and mitigation strategies.

The study, “Regionally distinct drivers of intensifying summer concurrent hot and dry events in China,” was published in Atmospheric and Oceanic Science Letters (DOI: 10.1016/j.aosl.2026.100858).