Water Watchers

By Holli Riebeek Design by Robert Simmon January 21, 2010

Dean Stevenson has farmed the plains of south-central Idaho most of his forty-seven years. Like all farmers, he worries about things like the price of sugar beets and malt barley or the cost of gasoline, but most of all, he worries about water.

He is right to worry. The 4,000 acres he farms with his father and brother receive on average a scant 10 inches of rain per year. The water that sustains the sugar beets, barley, wheat, and potatoes growing on Stevenson land is pumped from the Snake River Plain aquifer. Every drop is rationed.

Photograph of a farm in arid southern Idaho.
Agriculture is the largest industry in Idaho, but large areas of the state rely on irrigation to provide water for crops. Irrigated farms in southern Idaho use water from both the Snake River and the Snake River Plain aquifer. (Photograph ©2005 p.m.graham.)

Stevenson is part of a water district—the Magic Valley Ground Water—that helps manage water taken from the aquifer.In 2006, another irrigation district on the Snake River Plain, A&B, believed that some of the farms in its district had run short on water, resulting in a poor harvest. Because A&B has senior (older) water rights, Idaho law allowed them to issue a water call, a demand that junior water right holders, including Stevenson, draw less water from the aquifer.

NASA satellite image of the Snake River Plain.
Most of the farms strung out along southern Idaho’s Snake River Plain rely on irrigation. Annual rainfall as low as 10 inches (25 centimeters) per year, or less, isn’t enough to support crops in the region. (NASA image by the MODIS Rapid Response Team.)

The agency with the unenviable task of sorting out water calls is the Idaho Department of Water Resources. The agency keeps track of how much water is in the state’s rivers and ground water to ensure that Idaho has a viable water supply for all of its users—farmers, cities and towns, and natural ecosystems.

Idaho uses more water than any other U.S. state except California and Texas, the two most populous states. More than 90 percent of the water consumed in Idaho goes to irrigate 3.4 million acres of farmland, providing the economic base for the state. In recent years, some of the department’s most detailed information on how much water farmers consume has come not from water meters on the ground, but from innovative space-based estimates of the evaporation of water from soil and plants.

Photograph of irrigation in Idaho.
Throughout the U.S. West, including Idaho, water rights depend on seniority—people holding older rights have priority access to water over those holding younger rights. (Photograph ©2005 j o s h.)

The new method holds enough promise for Western water management—a challenge that population growth and climate change are likely to intensify in coming decades—that it influenced the design of the next satellite in NASA’s decades-old Landsat program, now jointly managed by NASA and the United States Geological Survey.

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