A new study reviewed how urbanization impacts water use. The work was done in Oregon's Willamette Valley and was conducted by Oregon State University economists. What they found is that urbanization doesn't necessarily mean an increase in water use.

The researchers modeled water use in the region for three metro areas, and what they found is that water use in growing cities in the region will stay about the same, or decline, when surrounding irrigated farmland is converted to housing.

The findings were published in the journal Land Economics.

The study involved modeling land and water-use changes in three urban areas in the valley. According to David Lewis, an economist at OSU's College of Agricultural Sciences and a co-author of the study, the work looked at land and water use for the next 70 years.

In a statement, Lewis noted that when people think about urban expansion and water use, "they think of a direct relationship. But that's not always the case," he says. "The doubling of population doesn't necessarily mean the doubling of water use."

The economists used historical data to develop a statistical model of land changes in three Oregon cities — Woodburn, Salem-Keizer and Eugene-Springfield.

Those three areas were chosen because of the surrounding ag land water-use types. For example, Woodburn is surrounded by farms with irrigated agriculture; Salem-Keizer has irrigated and rain-fed agriculture; and Eugene has very little irrigated ag in the area.

Effect depends on amount of water used
What they found is that the net effect of new development on water depends on the relative quantities of water consumed by farmers and urban households, and the key is irrigated ag. Study co-author Christian Langpap, an OSU economist, noted that "an acre of irrigated farmland uses more water than an acre of land for housing."

In modeling change over the next 70 years, the researchers took into account water law in the Western United States. Most Western states generally follow the late 19th-century prior appropriation doctrine. This is a seniority-based system that gives farmers the right to use water for irrigation as long as the land is use for agriculture.

When land is converted from ag to urban use, the new owner loses the ag water right, but can acquire other water rights that typically use much less water.

As state and regional planners look ahead at changing land-use types, this study offers insight on water issues.

The study was led by Daniel Bigelow, an OSU doctoral graduate who is now an agricultural economist at the USDA'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.

Source: Oregon State University