The Study: McDonald, R. and E. Girvetz. 2013. Two challenges for U.S. irrigation due to climate change: increasing irrigated area in wet states and increasing irrigation rates in dry states. PLoS ONE 8(6): e65589. doi:10.1371/journal.pone.0065589.
The Questions: Climate change models forecast higher average temperatures that will cause crop-growing seasons in the United States to become hotter and drier. How will this impact the irrigation needs of agriculture in the United States? And how will farmers respond to drier conditions?
Study Nuts and Bolts: The authors (both Nature Conservancy scientists) looked at how farmers use of irrigation varied in response to weather changes over a 20-year period (1985-2005). The researchers calibrated data on farmers’ responses to moisture deficit (the shortfall of water needed for crops) with future climate change trends through 2090, using 16 GCMs (global circulation models) for climate change under various emissions scenarios.
What They Found: Climate change will bring increased moisture deficits across the United States, with the largest deficits in the South and Southwest. These deficits will produce two key changes in U.S. agriculture: Arid or “dry” states (such as Montana, Idaho and Colorado) will need to increase the amount of water needed for irrigation, while “wet” states (ie, Kansas and Texas) will need to start irrigating areas that are currently rain-fed. Nationally, the average amount of water needed for irrigation will go from 850,000 gallons/acre to 898,000 –1,110,000 gallons/acre in 2090 (an increase of 5-30%) and the total area irrigated will increase by 11-54 million acres (an increase of 19-94%).
However, the authors also note a historical trend toward greater irrigation efficiency — a trend that, if it continues, could offset most of the predicted future demands on irrigation.
What Does It All Mean? Agriculture in the United States will need to adapt to future conditions: Places that are already irrigating are going to need to increase the amount of water they’re using, and places that aren’t irrigating much now will need to irrigate more areas. States that need to start irrigating face the biggest challenges: They are not currently set up for complicated water rights management like the more arid states, and are also not providing incentives for farmers to improve irrigation efficiency.
The authors also call attention to the role of reducing emissions: By avoiding the release of 1 GtC, the U.S. can save roughly 17 billion gallons in irrigation water annually.
For more insights, read study author Rob McDonald’s blog about how farmers will adapt.