Three new high-profile studies led by Dr. Yi Yao (Vrije Universiteit Brussel and ETH Zurich) show that while irrigation may be seen as a tool to dampen heat extremes, its benefits will come with adverse impacts.
In a first study published in Nature Communications examining historical irrigation data over 1901-2014, the team looked at how expanding irrigation has affected extreme heat conditions. Using six state-of-art Earth System models, to increase the robustness of the results, they found that irrigation has helped reduce the frequency of very high air-temperatures (“dry heat” extremes) in heavily irrigated regions. However, because irrigation also raises air humidity, its damping effect on “humid-heat” stress (exact term is wet-bulb temperature) was much weaker. “We know that for people, humid-heat can be more dangerous than dry heat. For the same absolute temperature, the humidity level greatly affects their capacity of coping with the heat stress” states Dr. Yi Yao, lead author of the study and a researcher at ETH Zurich, who performed this research during his PhD at the VUB. “We show in the study that in certain parts of the world, irrigation has made humid-heat stress worse. This may endanger millions of people who live in these areas” he adds.
In a second study published also in Nature Communications, the researchers looked into the future and projected how future greenhouse-gas emissions and irrigation practices together will shape the risks of dry and humid heat stress over the course of this century. For this, they performed future simulations with an Earth System model with varying emission pathways and irrigation scenarios. They show that while irrigation can help moderate dry-heat extremes somewhat, it cannot counter the overall warming trend. “Projections show that people will face many more hours of extreme humid heat each year — in some tropical regions, over a thousand extra hours per year compared to the past. These conditions will be extremely challenging to adapt to.” warns Prof. Wim Thiery, climate scientist at the VUB and senior author of both studies. “The study worryingly shows that irrigation will tend to amplify those humid-heat risks in places such as South Asia, where today already, life-threatening heat waves occur year after year. In a previous study we have calculated that about three quarters of the children born in 2020 in India will live through unprecedented lifetime exposure to heatwaves assuming we continue on our emission track.”
In the third study published in Nature Water, the team examined how the global spread of irrigation has affected freshwater resources over historical timescales. “Using seven advanced Earth System models as part of a model intercomparison exercise, we found that irrigation expansion since 1901 has greatly increased water losses from land through increased evapotranspiration, a depletion which has not been compensated by chances in local rainfall” explains Dr. Yao. This implies that due to rapidly expanding irrigation for agriculture, more water is leaving the land than returning to it through precipitation. This imbalance has caused significant regional water losses, especially in hot spot areas for agricultural irrigation. In some of these regions, land water storage has declined by up to 500 mm from 1901 to 2014 over South Asia and Central North America in particular. “Our study is raising alarm bells on the fact that both irrigation and climate change are depleting soils, rivers, and groundwater, raising concerns about long-term water security” warns Dr. Yao. “What is concerning is that major irrigation regions are already on unsustainable paths and call for urgent adoption of water-saving technologies: efficient irrigation methods, for example by installing drip or sprinkler systems, and shifting towards crops that require less water, to prevent further depletion of vital freshwater supplies” concludes Prof. Thiery.
These findings send a clear message: irrigation cooling the air isn’t the full picture — when heat is paired with humidity, irrigation actually enhances human health risks. Adaptation planning for rising impacts of climate change on agriculture must therefore go beyond just expanding irrigation. It must improve irrigation efficiency so that water resources depletion as well as human heat stress escalation are limited. And perhaps most importantly, we must cut greenhouse-gas emissions, today, to limit the worst effects of rising global temperatures.
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 emissions- and irrigation-induced increases in humid-heat stress. Nat Commun 16, 9326 (2025). https://doi.org/10.1038/s41467-025-64375-1
Yao, Y., Thiery, W., Ducharne, A. et al. Irrigation-induced land water depletion aggravated by climate change. Nat Water (2025). https://doi.org/10.1038/s44221-025-00529-1
Journal
Nature Water