How will climate change affect local rivers?

Changing climate could hurt late-summer flows

In addition to bringing longer wildfire seasons and warmer winters to Central Oregon, climate change stands to fundamentally alter the lifeblood of many of the region’s communities: its rivers.

Some river experts predict that a declining snowpack could cause massive declines in river flows throughout the Deschutes basin during late summer, the time of year when farmers, fish and other users need water the most.

“The key thing is: We need the snow, and we’re not gonna have it,” said Yancy Lind, a blogger and fisheries activist living in Central Oregon.

Tod Heisler, executive director of the Deschutes River Conservancy, said conventional wisdom has long been that the Deschutes basin is less susceptible to climate change than other river systems because many rivers in the basin are largely fed by underground springs rather than surface water.

The springs recharge when snowmelt high in the mountains seeps into the porous basalt rock, slowly seeping out at lower elevations to feed the Upper Deschutes and other rivers in the region. Heisler said this gives many of the rivers in the region a more stable source of water than those that rely heavily on snow runoff, allowing rivers to flow even with the dry climate.

“Despite the fact that we only get 12 inches of rain, we get all the benefits,” he said.

However, Lind noted the scope and scale of the natural underground aquifer varies widely throughout the basin. Downstream from Bend, near Crooked River Ranch and Lake Billy Chinook, Lind said the reserves are significantly greater than they are in other parts of the basin.

“There’s just an amazing amount of water in there,” Lind said.

However, the springs high in the mountains are shallower and take less time to deplete, Lind said. A few low snow years can leave reservoirs on the Deschutes River dangerously low, as they were earlier this year, when a series of drier-than-average winters contributed to the lowest levels seen at Wickiup Reservoir in six decades.

Whether or not climate change brings more overall precipitation to Central Oregon, Heisler said higher temperatures will certainly mean more of the precipitation falls as rain rather than snow at high elevation.

Additionally, Heisler said climate change may contribute to an acceleration of the water cycle that feeds rivers in the basin. In the past, the snowpack began to melt in late spring and even early summer. However, warmer winters and springs could contribute to snow melting earlier in the year, which would then leave less snow runoff later in the summer, when the weather is warmest and irrigation season is in full swing.

“If the peak used to be in June, maybe that’s now in March,” Heisler said.

Overall, Heisler said he’s seen projections that estimate a 40 to 60 percent decline in river flows in the Deschutes basin in July and August by 2040. While Heisler and Lind agreed that Central Oregon’s cities and towns will likely be fine in the short and medium terms due to their use of deep aquifers, the water shortages could dramatically affect farmers as well as native fish.

High-elevation, spring-fed tributaries like Whychus Creek and Tumalo Creek stand to be disproportionately affected, Heisler said. These creeks act as refuges for bull trout and other fish that need cold water to survive during the summer heat. With less water in the river, Heisler said some fish that call the creeks home could struggle to survive.

For farmers who rely on water stored in reservoirs along the Deschutes, the upcoming year could be a hint at a drier future. After water levels at Wickiup Reservoir were aggressively drawn down during the past irrigation season, it is unlikely that the reservoir will fill this winter. If spring and summer are dry again, junior water-right holders like North Unit Irrigation District, which relies heavily on Wickiup, may aggressively draw down the reservoir once more.

“If they’re not terrified of next summer, then they’re not paying attention,” Lind said.

Agencies looking at the future of water in the Deschutes Basin are looking at climate change as a contributing factor. The Upper Deschutes Basin Study, a collaborative effort involving more than 30 stakeholders designed to provide a resource for shaping the future of the basin, contains a section focused on climate change, according to Mike Relf, study lead for the U.S. Bureau of Reclamation.

Relf said the study uses computer modeling to examine how climate change may affect air temperature and changes to precipitation throughout the year. He declined to go into specifics, but said he expects a draft of the basin study to be released by the end of February.

Heisler said he was optimistic that a changing climate could generate support for additional water-­conservation measures in the basin. He pointed to canal-piping projects throughout the basin that are already underway as a way to make Central Oregon’s irrigation season more efficient. Additionally, Heisler said he’d like to see a system for sharing water between irrigation districts operating in the Deschutes basin, as well as an incentive program to encourage farmers to use water more efficiently.

“The bottom line for is we’re gonna have to do all of it,” he said.

— Reporter: 541-617-7818, shamway@bendbulletin.com