During the next 85 years, temperatures in Oregon’s
Willamette River basin are expected to rise significantly, mountain snowpack
levels will shrink dramatically, and the population of the region and urban
water use may double – but there should be enough water to meet human needs, a
new report concludes.
Fish may not be so lucky. Although ample water may be
available throughout most of the year, the Willamette Valley and its
tributaries likely will become sufficiently warm as to threaten cold-water fish
species, including salmon and steelhead, the scientists say.
These are among the key findings of the Willamette Water
2100 Project, a five-year, $4.3 million study funded by the National Science
Foundation and led by Oregon State University, in partnership with researchers
from the University of Oregon, Portland State University and University of
California at Santa Barbara.
“The Willamette River basin today is characterized by
abundant annual water and sometime seasonal shortages,” said Anne Nolin, an OSU
professor of environmental sciences and principal investigator on the study.
“That should continue into 2100, despite much warmer temperatures, more people
and a substantial loss of snowpack.
“The reason for optimism is the region’s 11 storage
reservoirs coordinated by the Army Corps of Engineers that act as a valve for
seasonal differences and preserve water for times of need,” Nolin added.
“Without them, the picture would look quite a bit different.”
Analysis of global circulation models suggest that the
Willamette River basin will warm between two and 13 degrees (Fahrenheit) by the
year 2100, thus scientists used three separate scenarios to look at potential
impacts based on low, medium and high rates of temperature increase. These
temperature increases will result in a dramatic decline in snowpack – from 63
to 95 percent lower than average – changing seasonal water flow patterns.
Scientists also explored results from a range of population,
economic and policy scenarios that allowed them to ask “what if?” questions for
different human changes and interactions with climate changes. Much of the
climate modeling for the project was developed through a regional integrated sciences
and assessments (RISA) program at Oregon State, which is funded by NOAA and led
by OSU Professor Philip Mote.
There is little doubt that temperatures will increase, the
report notes, but there is less certainty about the impact of a changing climate
on precipitation. Winters may actually be slightly wetter, though more of the
precipitation will fall as rain instead of snow. Summers should be drier,
necessitating more reliance on water held behind the region’s 11 storage
“Although there are a number of government entities –
federal and state – involved in regulating water use from those reservoirs,
there appears to be enough flexibility in the system to adequately adapt for
changing conditions in the future,” said Nolin, a professor in OSU’s College of
Earth, Ocean, and Atmospheric Sciences.
The report notes that warmer temperatures, less snowpack and
drier summers will greatly increase the danger of wildfire in the mountains
feeding the Willamette River basin – by about 200 to 900 percent. Their
simulations show that fire will open up lands to new forest types and reduce
the availability of forestland for timber harvest.
Increasing urban use of water from a population that could
double will involve costly expansions in infrastructure. As the population
grows, more agricultural land near urban areas will be developed for housing
and other needs, according to Samuel Chan, a watershed health specialist with
Oregon Sea Grant and the broader impacts outreach lead for the Willamette Water
However, the report shows that in some cases where urban
areas are expanding into what are now irrigated farmlands, these locations may
see a net decline in water use.
“The report notes the difference between water ‘diversions’
and water ‘consumptive use,’” Chan noted. “As the population grows, the need
for water will increase, but much of it will be used, and then treated in
wastewater plants and returned to the system. Other uses, like forests and
agriculture, consume the water through evaporation and transpiration to the
“The downside, though, is that treated water that is
returned to the river is often warmer, increasing the impact on cold-water fish
species,” he added.
The main drivers for changing water needs, the report
concludes, are climate change, and growth in population and income.
“The dams built above the Willamette Valley were engineered
for reducing the risk of floods, but they also do a valuable job in storing
water for use during summer,” Nolin said. “They can store large amounts of
water in the summer, when they are not kept empty for flood prevention and
there is existing flexibility in water allocation policies that could help
western Oregon adapt to a climate that may be quite different in the future.”
“Unlike many parts of the country, those of us who live in
the Willamette Valley are lucky because we have abundant water for human use,
and we have institutional capacity to help mitigate water scarcity,” she added.
“However, the biggest negative impacts are likely to be for native cold-water
fish and we will likely be facing a significant challenge in managing stream
temperature for fish.”