When soaring temperatures coincide with high humidity, the atmosphere can become suffocating, resembling the oppressive heat of a sauna. According to Professor Miaoni Gao, a climate scientist at Nanjing University of Information Science and Technology, “It’s no longer merely hot—it’s dangerous.” Unlike dry heat, which the body can somewhat alleviate through evaporation of sweat, humid conditions significantly hinder the body’s natural cooling mechanisms. This physiological limitation increases the risk of heat-related illnesses such as heat exhaustion and heatstroke, especially among those less capable of thermoregulation, including the elderly and young children. In eastern China, the convergence of intense heat and high humidity—known as compound heat–humidity extremes or humid-heat waves—is becoming alarmingly common and severe.
Recent research published in Atmospheric and Oceanic Science Letters by Professor Gao’s team shows a troubling trend. These compound extremes are not only increasing in frequency but are also lasting longer than ever before. Using climate data spanning from 1961 to the present, the researchers found that the active season for humid-heat events has notably expanded, particularly in the Yangtze–Huaihe region and in southern China. Over the past decade, for example, South China has experienced an extension of the humid-heat season by approximately one month. This prolonged exposure amplifies health risks, particularly for vulnerable groups whose physiological resilience to extreme weather is already compromised. Such findings suggest that climate change is not only warming the planet but is also reshaping the seasonal calendar in ways that directly impact public well-being.
The key driver behind this intensification is the westward expansion of the Western North Pacific Subtropical High, a dominant atmospheric system in the region. This climatic shift enhances solar radiation and channels persistent heat and moisture into eastern China, reinforcing both the severity and duration of these heat–humidity episodes. As these changes persist, they are fundamentally altering the seasonal structure of summer across much of the country, with peak heatwaves arriving earlier, lasting longer, and affecting broader swaths of the population. The implications are far-reaching, as traditional forecasting models and public health preparedness strategies struggle to keep pace with the rapidly evolving climate dynamics.
Heatwaves, however, are not merely inconvenient weather events; they constitute serious public health emergencies. In 2023 alone, over 37,000 heat-related deaths were recorded across China, with a disproportionately high impact on seniors and children. Professor Gao’s study reveals that physiologically vulnerable groups now make up nearly 39% of the population exposed to compound heat–humidity extremes. Alarmingly, about one-third of this increased exposure stems directly from the lengthening of the humid-heat season. In southern China, where humidity levels are persistently high, the proportion of affected individuals in these vulnerable categories surges to 56%. With China’s population continuing to age—more than 200 million citizens are now aged 65 or above—this confluence of demographic fragility and intensifying climate threats presents an urgent and growing challenge.
To address this evolving crisis, the researchers urge a rethinking of how heat warnings and public health interventions are implemented. “We can no longer rely on fixed-schedule summer warnings,” emphasises co-author Xinyue Sun. “We need dynamic early-warning systems that adapt to the shifting timing of heatwave seasons, as well as targeted health measures designed specifically to protect the most vulnerable.” Without timely adaptation, the intersection of prolonged humid-heat conditions and a rapidly ageing population could catalyse a nationwide health emergency. As eastern China braces for more intense and prolonged summers, responsive and proactive strategies—grounded in robust climate science and compassionate public health policy—are essential for safeguarding the well-being of millions.
More information: Miaoni Gao et al, Prolonged seasons of compound heat–humidity extremes amplify vulnerable population exposure in eastern China, Atmospheric and Oceanic Science Letters. DOI: 10.1016/j.aosl.2025.100663
Journal information: Atmospheric and Oceanic Science Letters Provided by Institute of Atmospheric Physics, Chinese Academy of Sciences
