Nature Communications: US irrigation water use could rise up to 44% in 2040–2070

Climate change is likely to intensify water demand in the United States mainly in certain seasons and regions, according to a study published on 23 October in the journal Nature Communications. It was written by Joey Blumberg and Travis Warziniack of the Rocky Mountain Research Station of the U.S. Department of Agriculture's Forest Service in Fort Collins; Blumberg is also affiliated with the University of Tennessee. The researchers analysed high-frequency data on water withdrawals from 2000 to 2020 – the measured part of the work. Building on that, they calculated how demand could develop in the period 2040 to 2070.

The projections are based on 28 scenarios with warming of between 1.0 and 2.9 degrees Celsius and population growth of between 1 and 44 percent. Water use for crop irrigation rises most: depending on the scenario, the authors calculate an increase in annual water use of 32.1 to 43.6 percent. For public water supply, the range is from minus 10.7 to plus 28.9 percent. For cooling thermal power plants, by contrast, the model shows a decline of 19.9 to 27.9 percent. The ranges reflect the spread across the 28 scenarios; the summary gives no confidence intervals. The distinction between the two parts matters: the withdrawal data are observed, while all values for 2040 to 2070 are model calculations.

The authors stress that the calculated changes are "contingent on continued adaptive efforts." Climate stress on water supply is therefore not a uniform nationwide effect but shows up mainly as seasonal mismatches between supply and demand and as shifting regional stress – and can be influenced by adaptation. The study has so far been published as an early-access version that may still be edited. It covers only the United States, and no direct conclusions can be drawn for Europe. It does show, however, how strongly pressure on water resources can shift between agriculture, households and power generation in a large farming country.