Irrigation, the largest human intervention in the water cycle.

A food crisis is coming.

• About 2.3 billion people faced moderate or severe food insecurity in 2021. FAO, 2022
• Global food demand may double by 2050, about 30% from population growth and 70% from diets shifting toward meat. Tilman & Clark, 2015
• 42% of the world’s irrigated area is in just two countries, China and India, home to almost 40% of the world’s people. Szilagyi et al., 2020

We need irrigation to grow more food.

• Irrigated land is at least twice as productive as rainfed land. World Bank

But then we would have a water crisis.

• About 70% of the fresh water people withdraw goes to agriculture, and over 90% in parts of the Middle East and South Asia. Foley et al., 2011
• About 40% of the world’s irrigated area, and about 60% in the United States, relies on groundwater, and groundwater depletion roughly doubled between 1960 and 2000. Wada et al., 2010

• It can turn evaporation from limited by water to limited by energy, changing the land’s water and energy budgets. Taylor et al., 2012
• Groundwater-fed irrigation has raised downwind rainfall and streamflow by up to 30% in the US High Plains and California’s Central Valley. DeAngelis et al., 2010 Kustu et al., 2011
• Less obviously, large-scale irrigation can suppress rain over the irrigated area itself. Szilagyi et al., 2020
• It cools the hottest days of the year. Thiery et al., 2020; Lawston et al., 2020
• It can delay the onset of monsoons. Tuinenburg, 2013
• It can create humid heat waves beyond what people can tolerate. Raymond et al., 2020; Wang-Erlandsson et al., 2022