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OSU model sees ‘modest’ water use growth in Willamette Valley


In Oregon’s Willamette Valley, urbanization doesn’t necessarily correspond to an increase in water usage, according to economists at Oregon State University.

Instead, they predict that water use in growing cities in the valley will stay about the same, or decrease, when surrounding irrigated farmland is converted to housing.

The findings are published in the journal Land Economics.

When the researchers simulated land use and water use changes in three urban areas in the Willamette Valley over the next 70 years, their model predicted only modest growth in water use despite large projected population increases, said David Lewis, an economist in OSU’s College of Agricultural Sciences and one of the study’s co-authors.

“When people think about urban expansion and water use, they think of a direct relationship. But that’s not always the case,” Lewis said. “The doubling of population doesn’t necessarily mean the doubling of water use.”

The net effect of new development on water depends on the relative quantities of water consumed by farmers and urban households. The key is irrigated agriculture, said Christian Langpap, an OSU economist and study co-author.

“What really matters is the type of land the city is expanding into,” Langpap said. “An acre of irrigated farmland uses more water than an acre of land for housing.”

The economists used historical data, to develop a statistical model of land-use change in three urban areas – Woodburn, Salem-Keizer and Eugene-Springfield. The model focused on those three areas because each is surrounded by different landscapes – Woodburn by irrigated agriculture, Salem-Keizer by irrigated agriculture and rain-fed agriculture, and Eugene, with very little irrigated agriculture.

For this model, the researchers looked at population growth, income and agricultural commodity markets, among other things. The model’s framework could be used to predict water use in other growing urban areas, Lewis said.

In their modeling, the researchers took into account water law in the western United States. Most western states generally follow the late-19th century prior appropriation doctrine, which is a seniority-based system that gives farmers the right to use water for irrigation as long as the land is used for agriculture. When land is converted from agriculture, the new owner loses the agricultural water right but can acquire other water rights that typically use much less water.

The study was led by Daniel Bigelow, an OSU doctoral graduate who is now an agricultural economist at the U.S. Department of Agriculture’s Economic Research Service. Also co-authoring the study was Andrew Plantinga, a former OSU economist who is now at the University of California, Santa Barbara.

The National Science Foundation funded the research through its Water Sustainability and Climate Program.

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