Water temperatures in Northwest streams will rise about half
as much as the expected air temperatures will rise due to climate warming
caused by greenhouse gases, challenging some fish species to shift their range
to seek cool water refuges in order to survive.
That was Dr. Dan Isaak’s message to the Northwest Power and
Conservation Council at its meeting this week in Portland. Isaak is a research
fish biologist at the U.S. Forest Service Rocky Mountain Research Station in
He said the region can help by creating more detailed
climate models combined with detailed fisheries models that have a resolution
down to as little as 1 kilometer of stream in order to create “spatially
Although the average temperature will “bounce around year to
year,” there is an undeniable warming trend and that is causing changes in
timing in the wild: flowers bloom, geese fly north and salmon migrate to the
ocean or return from the ocean, all earlier than in the past.
In fact, across all species, the timing of a specie’s
phenology (a certain point in a species’ life history, such as migrations) is
changing about two days every decade. For example, sockeye salmon migrations
from the ocean to spawning grounds have been occurring earlier by about 1.5
days per decade.
With this change, many species will seek the “thermal edge”
of their range and for salmonids in the Northwest that could be cool areas of
refuge where tributaries enter mainstem rivers or where cold springs bubble up
under a river’s surface, or it could be migrating further upstream where water
temperatures are cooler, including to the cooler water areas currently blocked
“Once we can identify some of these places (cool water
refugia), that will give us some assurance that these species will not go
extinct,” Isaak said. “Regardless, it will require an intergenerational
commitment. We’re only in the third inning of a nine inning baseball game.”
Despite the bio-complexity of salmon stocks in the Northwest
that will help buffer some of the future climate changes, some species may
still experience a long term decline and we won’t find refuges everywhere,
Isaak said. “We may need to be prepared to let some species go.”
Changes in air temperature are not homogenous across all
areas, but the warming trend over the past 44 years, he said, is 0.21 degrees C
(about one-half degree Fahrenheit) per decade. For example, the warming trend
is more pronounced in the Cascade Mountains than it is in Idaho.
That translates into an increase in water temperature of
0.11 degrees C (about 0.2 degrees Fahrenheit). Of the 245 sites in the
Northwest with at least 10 years of monitoring data, 98.5 percent of the sites
are showing a trend towards warmer water.
In addition, climate cycles are embedded in long term trends
and the Northwest had been in a cooler Pacific Decadal Oscillation phase, but
in January 2014 the PDO anomaly became warm and dry. Combined with a warming
climate trend, the region had record average temperatures, record low stream
flows and record warm water, Isaak said.
“Climate change is tilting the odds towards a more perfect
storm,” he said of the rapidly increasing air temperature, “and that will
happen at a higher frequency.”
While the future is uncertain, he said the bigger
uncertainty will be whether that means wetter or drier weather.
“We might have a slightly wetter future with seasonal
differences – wetter winters and drier summers,” Isaak said.
As for snowpack and water, the total annual runoff in the
Northwest has been decreasing over the past 65 years and total precipitation at
higher elevations has also declined.
“Given these uncertainties, we want to identify systems that
support salmonids,” Isaak said. “Cool water habitats are hedges against this
To that end, the region needs good local climate scenarios
“that will allow us to add more precision to what’s happening in streams, as
well as to what’s relevant for fish,” he said.
With the plethora of stream temperature data available in
the northwest, Isaak said that they can now identify stream resolution to about
every 1 kilometer (0.62 miles) and that can be used to identify the best stream
habitat projects that will help keep water cool, or where cool water refuges already exist.
An example is bull trout. Isaak, along with Dr. Mike Young,
at the U.S. Forest Service Rocky Mountain Research Station in Missoula, have
developed a bull trout probability map that shows bull trout distribution and
their potential range. Bull trout have a relatively narrow range of thermal
tolerance, but still, in a very worst case scenario in which water warms and
bull trout cannot find cool refuges in their native streams, they could survive
in eight cool water refuges scattered throughout the Northwest in a sort of Ark
They have also mapped steelhead habitat – fish that
currently occupy up to 25,000 kilometers of Northwest streams – by identifying
areas that are too warm and where pre-spawn mortality is high.
For example, Salmon River steelhead in Idaho have low
pre-spawn mortality while Willamette River steelhead in Oregon have high
Although most anadromous fish will have to travel through
warmer mainstem rivers, there are things that can be done to cool headwaters
where fish generally spawn. “Shading (with bushes and trees) is the most
important single factor that can be invested in to keep streams cooler,” Isaak
However, investments in trees and bushes to keep a stream
cool is only possible in smaller tributaries, not in larger rivers where the
distance between shorelines make it nearly impossible to cool with vegetation.
The only way to cool mainstem rivers is through the use of water from dams,
Also, more water will help keep streams cooler. “There are a
lot of water diversions and that can be helped through modernization of water
systems and water rights,” he said. Water diversions and water rights can also
be mapped and identified at the same high resolution as cool water refuge maps.
Isaak and Young developed the “Climate Shield” that uses the
high-resolution “Norwest” stream temperature scenarios developed from data
contributed by more than 80 agencies with crowd-sourced biological datasets.
With this they can develop accurate forecasts about specific streams that are
most likely to act as climate refugia for native fish. The study was published
online February 27 in the scientific journal Global Change Biology.
To learn more about what Isaak and Young are doing to map
cool water refugia, see their Climate-Aquatics Blog at http://www.fs.fed.us/rm/boise/AWAE/projects/stream_temp/stream_temperature_climate_aquatics_blog.html
For background, see:
-- CBB, November 6, 2015, “BiOp On Oregon Water Temperature
Standards Calls For State, Agencies To Protect Cold Water Zones,” http://www.cbbulletin.com/435504.aspx
-- CBB, October 23, 2015, “Climate Change (Rising Sea
Levels) Could Be Bad News For Lower Columbia Restoration,” http://www.cbbulletin.com/435363.aspx
-- CBB, March 13, 2015, “Study Develops Forecasts On Which
Columbia Basin Streams Will Serve As ‘Climate Refugia,’” http://www.cbbulletin.com/433372.aspx