by Gail Binkly | December 1, 2017 11:06 am
If you’re an angler, you probably have a favorite spot, maybe somewhere in the watershed of the upper Dolores River, above McPhee Dam.
But that favorite fishing hole may not support trout, salmon, or any fish at all in coming decades, thanks to the inexorable warming of the planet.
That was the message delivered by Duncan Rose, a past president of the Dolores River Anglers chapter of Trout Unlimited, in a presentation to the League of Women Voters of Montezuma County on Nov. 11.
Rose was co-director, with Matt Clark, of a study done by the anglers group and the Mountain Studies Institute to look at what might happen by the year 2100 to streams in the upper Dolores watershed.
The three-year analysis involved the work of two scientific consultants and about 3,000 volunteer hours for developing an adaptive-management framework for coldwater fisheries, Rose said.
The report was released in 2016.
Its conclusion, Rose said, is basically one of change. “Whether good or bad is up to the individual to perceive,” he said.
The various streams and reaches of the upper Dolores are a coldwater fishery, meaning one that supports basically trout, or salmonids. Rose said the 46 identified trout streams and 295 stream miles of viable trout habitat in the study area support four species (cutthroat, rainbow, cutbow and brown), kokanee salmon, and one species of char (brook).
Nearly every long-term perennial stream in the watershed has a viable trout population. However, Rose said studies indicate that “substantial systemic changes” are already under way and affecting both temperature and precipitation in the area.
The fourth National Climate Assessment, a congressionally mandated study by the U.S. Global Change Research Program whose first volume was released in November, found that, “Global annually averaged surface air temperature has increased by about 1.8°F (1.0°C) over the last 115 years (1901–2016). This period is now the warmest in the history of modern civilization.
“The last few years have also seen record-breaking, climate-related weather extremes, and the last three years have been the warmest years on record for the globe,” the report states. “These trends are expected to continue over climate timescales.”
Rose said the report predicts more episodes of drought for the American Southwest, especially from mid-century on. By 2035, droughts are expected to last two to five years; that may move to multi-decade droughts by century’s end.
“This is beyond the experience of post-Puebloan culture,” Rose said, adding that nothing like this has been seen since the late 13th Century, if ever during human history.
Rose said the Silverton-based Mountain Studies Institute, which conducts research into environmental issues in the San Juan Mountains of Southwest Colorado, hired an expert who ran 72 different models/scenarios regarding future climate in the area. These produced three possible “clusters” of climate potentials:
Rose said all 72 models found temperatures in the area were likely to steadily increase.
Precipitation may stay close to current models, he said, as half of the scenarios showed more and half less in the watershed. However, more of that precipitation will occur as rain and less as snow, with snow coming later in the year and higher in elevation.
“This will likely reduce the amount of available water,” Rose said, since rain moves much faster than snow, which melts slowly and percolates through the soil.
“This has huge ramifications for farming and ranching because it changes the amount and timing of flows,” he said.
Local data from the National Oceanic and Atmospheric Association from 1949 through 2012 indicates that at present the area is primarily moving back and forth from wet years to drought, in the “feast or famine” scenario. This seems to predict that coming years will bring droughts of greater intensity with periodic relief.
A warming earth will have altered interactions between the oceans and air. As temperatures increase, there will be more “virgo,” rain that never touches the ground because it evaporates before it can hit.
Precipitation is closely tied to elevation, he said.
“If we did not have the mountains we have, we would not have fisheries here,” Rose said. For instance, in the LaSal Mountains in Utah, there is just a single trout stream, while the Abajos – also lower-elevation mountains – have three.
“Those mountains aren’t high enough,” he said. “You have to get to 12,000 or 13,000 feet in this area before you get substantial rain.” Lizard Head Pass, at about 10,000 feet, sees 54 inches of precipitation a year vs. 18 inches in the town of Dolores, elevation 6,900 feet.
But even higher elevations can’t protect the entire watershed from climate change. A 7-degree (F.) increase in temperature means a 29 percent reduction in stream flows on the Western Slope, Rose said.
And as air temperatures rise, water temperatures will follow.
“Lower, wide, slower, non-shaded streams may no longer support coldwater species by 2050 or 2070,” he said. That’s because warmer waters reduce growth, fertility and disease resistance in coldwater species.
“Trout may migrate upward,” he said, “but that higher habitat is smaller.”
Trout habitat will be increasingly threatened because of increased sedimentation resulting from wildfires, more trees dying because of beetle kills, and reduced flows.
“Some stream flows will be reduced periodically, some permanently.”
The streams most likely to retain their coldwater fisheries, he said, will have large areas of watershed at higher elevations, many feeder streams, a moderate gradient, and narrower walls that keep them more shaded.
Of the 46 trout streams, East Fork is the least vulnerable, Rose said, with some of the most vulnerable including Lost Canyon Creek, Ryman Creek, Taylor Creek and Rio Lado.
Fens and wetlands will become more valuable as the century marches forward, he said.
Twenty-nine streams in the upper Dolores watershed are home to cutthroat trout, the only native trout in Colorado. “But some of our best cutthroat streams are the most challenged,” Rose said. “Even Fish Creek will be challenged because of temperatures.”
He said potential management strategies include:
“This is a huge stage that’s being set,” he said. “It’s a train wreck that’s coming.”
2002 saw the worst drought in recorded history in the area. Stream-gauge flows at Rico that year were compared to average daily flows for 62 years, and the average daily flow reduction was 44 percent across 365 days, Rose said. “If you have that size of a reduction five years in a row, what does that mean for the governance structure in our community?” he asked. “There are some real ramifications.”
But the change is coming.
“Climate change is persistent and relentless,” he said. “Many streams and reaches in our area will face very serious challenges and changes as we move toward 2100. Many will become warm-water fisheries or will simply dissipate.”
He quoted the famous prayer by Reinholt Neibuhr: “God, grant me the serenity to accept the things I cannot change, the courage to change the things I can, and the wisdom to know the difference.”
In this case, he said, knowing the difference means knowing where to invest money and effort to save streams, and where to simply let change happen.
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