By Brian Charles Clark, Washington State Magazine
Until recently, a climate-change induced shift in water supply was the story of the Columbia River Basin’s future. But as researchers continue to fine tune climate models, shifting demand for water now must be accounted for, say Washington State University scientists.
Because the region depends on snowpack accumulation in winter to supply spring and summer irrigation water, the climate warming-induced shift in precipitation type had researchers and resource managers worried. If there’s more rain and less snow, how will there be enough melt water to feed the irrigation system through the warm times of the year?
Supply and demand are accounted for in a recent paper by WSU assistant research professor Kirti Rajagopalan and colleagues. Rajagopalan is a researcher with the Center for Sustaining Agriculture and Natural Resources in the College of Agricultural, Human, and Natural Resource Sciences. As WSU hydrologist and co-author Jenny Adam puts it, “The context of Kirti Rajagopalan’s paper is that we have to bring demand into the analysis.”
But that’s a big if. Rajagopalan and her colleagues are building a regional-scale climate model that attempts to embrace the complexity of the Columbia River Basin.
“For decision making at regional scales you really need to look at impacts of the changing climate on water supply and demand together,” Rajagopalan says, noting that most climate change impacts studies are at either the local or global scales, leaving a gap in the middle at the regional scale. Her new study looks at the implications of the changing climate on irrigation demands on a regional scale, the Columbia River Basin, for the next 20 years. “That’s the time frame in which infrastructure and other water-resource related decisions are made.”
“Most climate change and agriculture research focuses on cereal grains–they provide the most calories for most people in the world,” Rajagopalan says. “Or of late, there are people who are looking at high-value crops. But when you look at aggregate responses to water, the low-value crops are really critical.”
One of the innovative aspects of the new study produced by Rajagopalan and her colleagues is that they use information about what is being grown where to help determine water demand over the course of a growing season. This more specific mapping of cropping systems provides a much more realistic picture of water demand compared to models that base predictions on single crops.
Annuals, which include important Washington crops such as potatoes and wheat, will, in a warming regime, be planted and irrigated earlier. Once harvested, no more water is needed. Perennials, in contrast, which include apples and grapes, would likewise be harvested a little earlier but the trees and vines would need continued irrigation, so demand does not decrease as much over the course of a growing season.
Low-value crops include hay and alfalfa which “tend to extend for a longer season,” inasmuch as multiple cuttings of alfalfa can be produced in a season, Rajagopalan says. If growers decided to produce multiple cuttings of alfalfa over the course of a warmer and longer growing season, water use would go up.
Growers might potentially want to do something else with that water than irrigate a low-value crop. However, because of the current state of water rights, farmers often have little option with water except to use it or lose it. If that system of water rights management can be made more efficient, for example by better use of water markets in which water could be leased to another user without penalty to the rights holder, then farmers might benefit from that flexibility. And so would other uses, such as if the water is leased to support more flow for fish.
And it is likely that water rights management and governance will need to be reconsidered in the light of a warming climate. As Rajagopalan explains, “Water rights are given for a specific time,” typically April through October. “But if you’re thinking of planting earlier and need water earlier, there have to be changes to the system to allow that.”
“Impacts of near-term regional climate change on agriculture in the Columbia River basin” by Rajagopalan et alia appears in Water Resources Research, 54, 2125-2182.
The research was funded by the BioEarth project—Department of Agriculture, National Institute of Food and Agriculture, and the Forecast project—Washington Department of Ecology.
See a related story on the Columbia River from Washington State Magazine, “A River Rolls On.”