See how half of the Treasure Valley’s farmland could disappear by 2100

Boise children visit sheep farm

Cleo and Duane Gallinger love sharing their farm and their sheep with children in this September 2009 video.
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Cleo and Duane Gallinger love sharing their farm and their sheep with children in this September 2009 video.

When the Census Bureau announced in December that Idaho was the fastest-growing state in the nation, it hardly came as a surprise to the Treasure Valley’s increasingly crowded and cranky residents.

It’s obvious where today’s new arrivals are – filling the streets, spurring Downtown Boise construction, setting up households in new developments where there once was open space. Just think Meridian. The big question, though, is where tomorrow’s newcomers will end up.

A group of Boise State University researchers has some ideas about that, along with a warning or two. In a detailed study and a series of online maps, they lay out possible scenarios for urban growth in this decreasingly agricultural region.

“Our projections demonstrate that urban expansion replaces agriculture, wetlands, forested areas, and sagebrush-steppe, with the largest losses [occurring] in agricultural areas,” says the report, “Projecting Urban Expansion in the Treasure Valley to 2100.”

Ada and Canyon counties today are home to 669,830 people, according to the Community Planning Association of Southwest Idaho. The Boise State study estimates that the region could grow to between 1.25 million and 1.75 million people by 2100.

In the scariest scenario, between 59 percent and 64 percent of the region’s farmland will disappear by 2100. That’s between 190,000 and 220,000 acres lost to low-density development, about four times the size of Boise.

A rosier picture could be attained in part through careful planning and construction that goes up, not out, according to the researchers, who are part of a program funded by the National Science Foundation called MILES, or Managing Idaho’s Landscapes for Ecosystem Services.

That would cut farm loss more or less in half, the researchers predict, with just 31 percent of the region’s current agricultural land turning into urban space in the next 80 or so years. An estimated 110,000 acres would be lost.

An animated GIF in the researchers’ online mapping project shows a time lapse of Ada and Canyon counties and environs. The background map portrays craggy mountains, brown high desert and green agricultural land and forest.

The starting point is a 1938 slide. It shows tiny blue-colored splotches of urban development, mostly around Boise, Nampa and Caldwell. By the time 2020 rolls around, the urban blue has spread into a mass that envelops Boise, Meridian, Eagle, Nampa and Caldwell.

By 2100, one huge, nearly solid blue splash reaches from Lucky Peak Reservoir west to Parma, with a little lacy green farmland around the edges. Thin blue threads of development wend their way into arid high desert southeast of Kuna and Melba.

Treasure Valley 1938
In 1938, urbanized Treasure Valley was miniscule, represented by the blue splashes in this map. Jenna Narducci and Ana Costa Boise State University

Treasure Valley 2014 (2)
By 2014, thousands of acres of farmland had been gobbled up by development, as seen in blue, spurred by the Treasure Valley’s growing population. Jenna Narducci and Ana Costa Boise State University

Treasure Valley 2100
If the most dramatic projections come to pass, the Treasure Valley population could grow to 1.25 million and as many as 220,000 acres of farmland could disappear. Jenna Narducci and Ana Costa Boise State University

“The main takeaway is, if we keep developing in a business-as-usual fashion, we could lose a lot of the amenities and qualities of Boise that people have grown to love and why people move here,” said Jenna Narducci, a BSU geosciences graduate student and lead author of the report. Narducci worked under the direction of Jodi Brandt, an assistant professor and head of Boise State’s land-use lab.

The study was the first step in a larger effort to understand how water resources in the region will change in the future. A website and conference focusing on water resources in the West are in the works for spring.

“It’s pretty shocking to see all that ag land going away,” said Shawn Benner, a professor of geosciences at Boise State. “This is a plausible outcome. It gives people something to point to – we’re going to lose half of our agricultural land.”

That’s the bad news. The good news, Benner said, “is that, depending on how we develop and grow, the relative consumption of ag land in our valley is dramatically different. … Those differences in growth will have dramatic impacts on water supply, air pollution and infrastructure costs.”

This story has been corrected. An earlier version misstated the combined populations of Ada and Canyon counties. Maria L. La Ganga: 208-377-6431, @marialaganga

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