Researchers, including Professor Iestyn Woolway, a NERC Independent Research Fellow at Bangor University, have published a paper examining these “compound heatwaves” in Nature Geoscience.
A heatwave is defined as an extended period of hot weather relative to the expected conditions of the area at that time of year.
As record-breaking heatwaves disrupt global water, energy, and food systems, the study analysed 796 river basins in the United States and Central Europe to find out what was happening.
By combining water quality observations with an AI deep learning model, they discovered that compound heatwaves have increased by about 0.40 events per decade since the 1980s. Forty years ago, these events occurred less than once a year on average. Today, they occur more than twice a year, meaning they have become around three times more frequent.
This trend coincides with the rapid intensification of heatwaves in rivers, which have increased in frequency (114%), duration (148%), and intensity (95%) between 1981–1990 and 2010–2019, far outpacing changes in atmospheric heatwaves.
Compared with isolated heatwaves in rivers, compound heatwaves drive an additional 16% rise in water temperature and a further 2.9% decline in dissolved oxygen. The study warns that under a high-emissions scenario, 98.5% heatwaves in rivers will coincide with heatwaves in the atmosphere by 2100.
Professor Iestyn Woolway said, “The findings of this study highlight the escalating threats of compound heatwaves to freshwater ecosystems and the need to incorporate their dynamics into future water risk assessments. Global temperature records continue to be broken, intensifying heatwave risks to public health, energy infrastructure and global economies. Atmospheric heatwaves are becoming more frequent, longer-lasting and more intense worldwide.
“Recent evidence, including the intense 2024 heatwave across the Western US, illustrates the growing potential of atmospheric heatwaves to elevate wildfire risk and amplify social and economic impacts. As climate warming continues, heatwaves in the atmosphere are projected to further escalate, making heatwaves a heightened feature of future climate risk. Rivers are highly sensitive to climate change. Excessive river warming can threaten aquatic life, disrupt ecosystem metabolism and exacerbate chemical pollution.”
Other institutions involved in the study include Hohai University, Nanjing, the Ministry of Water Resources, China, Yangzhou University, the University of Science and Technology of China, the Chinese Academy of Sciences, the University of California, USA, and Utrecht University, the Netherlands.
All authors contributed equally to this work.