ICAS external seminar

ICAS external seminar - Wim Thiery (Vrije Universiteit Brussel)

“Irrigation versus global warming”

Followed by coffee and cake in the SEE Foyer


Irrigation sustains global food production and many regional economies. The practice thereby also affects climate conditions - and especially hot extremes - in various regions across the globe. Yet how the climatic effects of past irrigation expansion compare to other anthropogenic forcings is still largely unknown. Here we provide observational and model evidence that expanding irrigation has dampened historical anthropogenic warming during hot days, with particularly strong effects over South Asia. We show that irrigation expansion can explain the negative correlation between global observed changes in daytime summer temperatures and present-day irrigation extent. While global warming increases the likelihood of hot extremes almost globally, irrigation can regionally cancel or even reverse the effects of all other forcings combined. Around one billion people (0.79-1.29) currently benefit from this dampened increase in hot extremes, but only because irrigation massively expanded throughout the 20th century. This effect may however level off as irrigation efficiency improves and its areal spread stagnates, leading to accelerated warming in intensely irrigated regions. Our results therefore highlight that irrigation substantially reduced human exposure to hot extremes but suggest that this benefit may be lost towards the future.