Hardly a month goes by without a heatwave occurring somewhere on our planet: January? Australia. February? Brazil. March? Central Asia. And so on. These prolonged periods of intense heat stress are becoming increasingly frequent, posing severe threats to human health, economic productivity, livestock, and ecosystems in a world that is getting warmer – and more humid.
One critical but often overlooked aggravating factor of heatwave impacts is air humidity: High humidity limits the ability of the human body to cool down through sweating, significantly increasing heat stress. This is especially the case in already hot and humid tropical regions because physiological thresholds may be crossed more often there. Compounding this issue, populations are also especially vulnerable in these regions: limited capacities for heatwave prediction, little access to healthcare, drinking water, and electricity, etc. Despite these risks, the underlying drivers of heatwaves remain poorly understood.
Addressing this knowledge gap, UKCEH researchers Dr Guillaume Chagnaud, Prof Christopher Taylor, and Dr Cornelia Klein, in collaboration with researchers at the University of Leeds, used a high-resolution, pan-African climate model simulation to study how localised soil moisture variations influence heatwaves. They showed that under favourable large-scale atmospheric conditions, areas with unusually wet soils spanning just a few 10s of kilometres across – reflecting the width of a typical rain event – can amplify heatwaves locally by 0.5–0.6 degree C.
Lead author Dr Guillaume Chagnaud said: "Importantly, the study suggests that this amplifying mechanism is at work in locations around the world where the first hundred metres of the atmosphere are strongly influenced by the soil moisture state, regions such as the Sahel in Africa, Northwestern India, Northern Australia and the Southeastern US which are vulnerable to hazardous heatwaves.
"Our research opens a promising avenue to exploring heatwave forecasting for such regions at lead times ranging from a few hours up to one day by combining weather model information with near-real time satellite observations of the land surface state."
Jemimah Gacheru, Principal Weather Forecaster at the Kenyan Meteorological Department (KMD) and Visiting Scientist at UKCEH under the NC-International programme, underscored the need for such tools. "There is limited awareness in Kenya and elsewhere regarding heatwave risks and impacts among a wide range of practitioners and society in general," she said.
Ongoing and future UKCEH work in collaboration with national weather services in tropical regions (including GMet in Ghana, ANACIM in Senegal, and KMD) will support efforts to increase awareness and build capacity – crucial steps towards mitigating the adverse consequences of heatwaves.
Related links
Full study: Chagnaud, G, Taylor, C M, Jackson, L S, Birch, C E, Marsham, J H, & Klein, C. (2025). Wet-bulb temperature extremes locally amplified by wet soils. Geophysical Research Letters, 52, e2024GL112467. https://doi.org/10.1029/2024GL112467