Study: Summer water supply to dwindle

Population growth will ramp up demand for water in arid Eastern Washington over the next 20 years, even as climate change alters flows in the Columbia River and its tributaries, a new study says.

By 2030, cities are expected to divert 24 percent more water to serve rapidly growing populations. But a warmer climate will diminish the Columbia Basin’s water supplies during the critical summer months, when farmers are irrigating crops, salmon are migrating and residents are trying to keep their lawns green.

“Generally speaking, the Pacific Northwest has enough water to meet most of our needs most years,” said Chad Kruger, director of Washington State University’s Center for Sustaining Agriculture and Natural Resources.

Though the volume of water in the Columbia Basin isn’t expected to change, climate modeling predicts that more precipitation will fall as rain instead of snow. That will reduce the mountain snow packs that fill reservoirs during the summer months, Kruger said.

To plan for alterations in stream flows, the study looks at future water supply forecasts and expected demands from communities and the agricultural industry, as well as flows needed to provide fish habitat.

The study’s conclusions will help the Washington Department of Ecology determine where to invest money in water storage projects, Kruger said.

The study, which is still in draft form, will be discussed Friday at a workshop at WSU’s Spokane Extension Office. WSU did the research work in conjunction with the state Ecology Department and the state Department of Fish and Wildlife. Their work was peer-reviewed by scientists in other states.

“For the first time, we’ll have a comprehensive evaluation of what our water needs will be in the Columbia Basin,” Derek Sandison, head of the Ecology Department’s Office of Columbia River, said in a statement. “This report provides a blueprint for how we invest in water supply projects. It will tell us where and when more water is needed in Eastern Washington.”

The study says the Columbia River Basin is particularly sensitive to small changes in overall temperature. Climate modeling predicts warmer, wetter winters, when demand for water consumption is relatively low. Water demand peaks in the summers, which will be hotter and drier than in the past, the study says.

Hotter summers will boost demand for agricultural irrigation, which is by far the largest water user in the Columbia Basin. Climate change could shorten the growing season for some crops, the study says.

Kruger said the study is cutting edge in that it looked at about 30 different crops grown in Eastern Washington, trying to determine future water needs. Since many crops are exported, the study’s modeling also used global economics to project demand for future crops.

“Water has been a controversial issue,” Kruger noted. The forecasting in the study “tries to do something to solve these issues.”