Southwest will be hit especially hard
Most agriculture in the southwestern U.S. is already marginal, possible only because U.S. taxpayers support cheap water for questionable crops. And because of global warming, the outlook is grim as the region continues to warm and dry.
By 2050, Arizona cotton production will drop to less than 10 percent of the crop yield under optimal irrigation conditions, a new MIT study projects. Similarly, maize grown in Utah, now only yielding 40 percent of the optimal expected yield, will decrease to 10 percent with further climate-driven water deficits.
Water shortages in the Great Basin will result in big drops to irrigated forage crops, including hay and grasses. By contrast, water stress could decrease in the Southern Plains, which could boost production of irrigated sorghum and soybean.
“In the Southwest, water availability for irrigation is already a concern,” says first author Elodie Blanc, a research scientist at MIT’s Joint Program on the Science and Policy of Global Change. “If we mitigate, this could prevent added stress associated with climate change and a severe decrease in runoff in the western United States. But it will be even worse in the future if we don’t do anything at all,” said Blanc, lead author of the research published in the journal Earth’s Future.
The study is unique because it tries to take into account how climate change will affect the water available for irrigation. The scientists also included factors like population and economic growth, as well as competing demands for water from various socioeconomic sectors, which are themselves projected to change as the climate warms.
The study modeled 99 river basins across the country, combining water data with simulations of economic, demographic, trade, and technological processes. The models also include the greenhouse gas emissions and other pollutants that result from these processes, and they incorporate all of that information within a global climate model that simulates the physical and chemical processes in the atmosphere, as well as in freshwater and ocean systems.
By 2050, the team projects that, under a business-as-usual scenario, in which no action is taken to reduce greenhouse gases, a number of water basins in the U.S. will start experiencing water shortages. Several basins, particularly in the Southwest, will see existing water shortages “severely accentuated,” according to the study.
The researchers said the basins that will be the most affected generally do not supply the largest areas of irrigated cropland. For example, though climate change will significantly reduce cotton production in the Southwest, the bulk of the country’s cotton production does not occur in this region.
“It may not matter too much for the total crop production of the U.S., but if you’re a farmer in that particular region that’s going to be impacted, that matters to you,” said co-author Erwan Monier. We also want to make clear that climate mitigation is better for U.S. irrigated agriculture than not doing anything.”
Going forward, the researchers plan to factor into their simulations various ways in which climate change drives adaptation, and how such adaptations in turn shape crop patterns and the agricultural landscape.
“In the real world, if you’re a farmer and year after year you’re losing yield, you might decide, ‘I’m done farming,’ or switch to another crop that doesn’t require as much water, or maybe you move somewhere else,” Monier said. “That’s the next step: How would the agricultural sector adapt?”