Global agricultural practices exacerbate heat stress and pressure on water resources, warn VUB researchers
With population growth and rising food demand, the area of land equipped for irrigation has increased almost six-fold worldwide since 1900. New research, published in three scientific papers led by the Vrije Universiteit Brussel (VUB) and ETH Zurich, shows that this rapid expansion of irrigation is having increasing effects on the health of populations, due to more intense wet heat stress and increased pressure on water resources. These results underline the need to improve irrigation efficiency worldwide, particularly in regions subject to water scarcity and high agricultural demand. They also serve as a reminder of the importance of reducing greenhouse gas emissions in order to limit the impact of climate change on agricultural production and food security.
Three major studies, led by Dr Yi Yao (Vrije Universiteit Brussel and ETH Zurich), show that while irrigation is often perceived as a means of mitigating heat extremes on agriculture, its benefits are accompanied by significant negative effects.
In a first study published in Nature Communications, the researchers analyzed historical irrigation data over the period 1901-2014 to assess the influence of its expansion on extreme heat conditions. using six Earth System models, ensuring the robustness of the results, they found that irrigation reduced the frequency of very high air temperatures - the extremes of ’dry heat’ - in heavily irrigated areas. However, by also increasing air humidity, irrigation mitigated humid heat stress (measured by wet bulb temperature) much less. we know that for human beings, humid heat can be more dangerous than dry heat. For the same temperature, humidity levels strongly influence the body’s ability to cope with heat stress’, explains Dr Yi Yao, lead author of the study and a researcher at ETH Zurich, who carried out this work as part of his thesis at VUB. ’ We show in the study that, in some parts of the world, irrigation has exacerbated wet heat stress. This could endanger millions of people living in these areas’, he adds.
A second study, also published in Nature Communications, looks to the future and examines how greenhouse gas emissions and irrigation practices will together influence the risks of dry and wet heat by the end of this century. The researchers carried out simulations with an earth system model incorporating several emissions and irrigation scenarios. They show that, while irrigation can help moderate dry heat extremes somewhat, it cannot counteract the overall warming trend. ’ Projections indicate that populations will have to cope with many more hours of extreme wet heat each year - in some tropical regions, more than a thousand hours more than in the past. These conditions will be extremely difficult to cope with’, warns Prof. Wim Thiery , climatologist at the VUB and senior author of both studies. ’ The study shows worryingly that irrigation tends to amplify the risks associated with humid heat in regions such as South Asia, where life-threatening heatwaves already occur year after year. We have calculated in another recent study that around three quarters of children born in 2020 in India will experience unprecedented exposure to heat waves in their lifetime if we continue our current emissions trajectory’, he adds.
In a third study, published in Nature Water, the team looked at the effects of the global spread of irrigation on freshwater resources through time. ’ Using seven advanced earth system models as part of a comparison exercise, we found that the expansion of irrigation since 1901 has significantly increased terrestrial water losses through evapotranspiration, a loss not compensated for by increases in local precipitation ’, explains Dr Yao. In other words, due to the rapid expansion of agricultural irrigation, more water is escaping from the land than is returning through rainfall. This imbalance has led to significant regional water losses, particularly in key agricultural areas. In some of these areas - notably South Asia and north-central North America - terrestrial water reserves declined by up to 500 mm between 1901 and 2014. ’ Our study sounds the alarm: irrigation and climate change are depleting soils, rivers and water tables, jeopardizing long-term water security’, warns Dr. Yao. what is particularly worrying is that the main irrigated regions are already following unsustainable trajectories. There is an urgent need to adopt water-saving technologies: more efficient irrigation methods - such as drip or sprinkler systems - and less water-intensive crops, to avoid further depletion of essential freshwater resources ’, concludes Prof. Thiery.
This work sends out a clear message: cooling the air through irrigation only tells part of the story. When heat is accompanied by humidity, irrigation actually increases the risks to human health. Adaptation planning in the face of the growing impacts of climate change on agriculture must therefore go far beyond simply expanding irrigation. It must aim to improve its efficiency in order to limit both the depletion of water resources and the intensification of heat stress. Above all, it is imperative to reduce greenhouse gas emissions now, to contain the worst effects of global warming.
References
Yao, Y., Ducharne, A., Cook, B.I. et al. Impacts of irrigation expansion on moist-heat stress based on IRRMIP results.Nat Commun 16, 1045 (2025) . https://doi.org/10.1038/s41467-025-56356-1
Yao, Y., Satoh, Y., van Maanen, N. et al. Compounding future escalation of emissionsand irrigation-induced increases in humid-heat stress.Nat Commun 16, 9326 (2025). https://doi.org/10.1038/s41467-025-64375-1
Yao, Y. et al, Nature Water (2025), xxxx.
