When extreme heat and drought coincide as concurrent hot and dry events (CHDEs), their combined impacts far exceed the damage brought by heatwaves or droughts in isolation. These compound extremes trigger widespread crop failures, deplete freshwater reserves, escalate wildfire likelihood, and elevate population mortality risks related to heat and dehydration. Against global warming, most prior research has centered on tracking how often CHDEs occur nationwide, yet few systematically unpack the physical drivers behind the growing severity, or intensification, of such events.
A new study led by Professor Qin Su's team at Yunnan University, China, addresses this critical research gap. The study confirms pervasive intensification of summer CHDEs across China and reveals that the identical-looking worsening hot-dry conditions stem from vastly different physical driving mechanisms with stark regional disparities. This research has recently been published in Atmospheric and Oceanic Science Letters .
The team systematically investigated the entirely separate physical mechanisms of intensifying trends of summer CHDEs in the two major high-risk zones: western China and east-central China.
"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."
Another striking supplementary finding is provided that areas witnessing the fastest growth in CHDE intensity are predominantly situated on the leeward sides of large topographic features.
This topographic pattern can be explained by adiabatic atmospheric processes. The 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 elevates air temperature and generates hot and dry air on the leeward sides. Under global warming, these inherently dry and hot baseline environments further amplify the increasing trend of heat and drought severity, making leeward regions particularly vulnerable to increasingly severe compound extremes. Su notes, "Topography cannot be ignored when projecting future hot-dry hazards, especially for mountainous and foothill regions."
These findings deliver solid theoretical foundations for developing early prediction and warning technologies for CHDEs, and provide critical scientific support for refined climate risk governance as well as targeted regional disaster prevention and mitigation strategies.
