Scientists saw that stream flows were declining in the Pacific Northwest over the past 60 years, but could not find a good answer why.
They thought it had to be either from increased evaporation or lower precipitation, explained Charlie Luce, a U.S. Forest Service hydrologist with the Rocky Mountain Research Station's Aquatic Sciences Laboratory in Boise. But the precipitation data didn't correspond with where the lower stream flows were showing up. And the evaporation explanation would have required far higher increases in sun radiation than had been measured.
Luce, one of seven Idaho climate scientists who will speak at the Downtown Boise Public Library this month, first figured out the data didn't correspond because the long-term precipitation gauges were at lower elevations. Higher snowpack measuring sites go back only about 20 years - not long enough for valid information.
Other research pointed to increasing wildfire area as a cause. But then Luce and his team, which included scientists from the University of Idaho, came up with a new explanation for declining precipitation in the high-altitude mountains that are the Northwest's primary water source: A decrease in winter winds.
Winds are highly variable and tied to cyclical events in the Pacific like El Nino. They hit mountain ranges with moisture-soaked air that turns into rain and snow. This process is called orographic cooling and, like so many other climatic processes, is becoming more variable as the globe warms.
"The windy years are as windy as ever," said Luce, "but in the least windy years, the wind is going down really fast."
Luce recently published his research in an article titled "The Missing Mountain Water" in the journal Science. He and the other scientists will speak on how climate change is affecting Idaho's natural and economic systems.
Luce's work is not just theoretical. Managers and policymakers are studying a new dam on the Weiser River and the possibility of raising Arrowrock and Island Park dams to capture more water. Idaho is seeing more rain instead of snowfall in the winter, along with the decreasing precipitation from reduced winter winds.
If engineers hope to offset those effects by building more dams, Luce said, they need to study closely how much water they can expect to capture, especially in the driest years.
"I'd frame it as an engineering problem," Luce said, "so they make sure they don't overbuild."
Dan Isaak is a fisheries researcher at the U.S. Forest Service who has shown that stream temperatures have risen in many Idaho waters and how, if the trend continues, bass may replace trout in some places.
"There's not much wiggle room for them to avoid the effects of warming," he wrote, "and (fish aren't) going to evolve legs in the next few decades, climb out of the water and walk to cooler habitats."
Other speakers in the Boise library series include University of Idaho hydrologist Zion Klos, who works with Luce, and prominent fire scientist Penny Morgan. Boise State University's Kerrie Weppner will share her research on fire over the millenniums and tree records that show what's happened in Idaho's forests.
U of I hydrologist Jae Ryu will discuss how climate affects long-term strategies for water storage and use. Scott Lowe, who chairs the Environmental Studies Department at BSU, will address how climate change could affect all manner of resources as farms and cities grow in Idaho.
Rocky Barker: 377-6484