What to expect in our mountain forests as the climate warms — The Mountain Town News

Dead spruce trees dominate the view from the Wolf Creek ski area in southern Colorado. 2014 photo/Allen Best

From The Mountain Town News (Allen Best):

And what remains uncertain

Runoff has begun, the streams and creeks soon to roar as the deep snowpacks of this year’s full-throated winter melt in Jackson Hole, Ketchum, and other mountain towns of the West.

But runoff this year, if it hews to trends of recent decades, will peak earlier, leaving a longer and probably hotter summer. Temperatures have been rising globally, with the three hottest years on record occurring in the last three years.

This warmth is driving changes in trees, and by enabling more rapid infestations by bark beetles and other pathogens. During the longer dry season, this also makes forests more vulnerable to fire, according to experts at a recent forum in Colorado sponsored by a group called Carpe Diem West.

The general trend described by Tony Cheng, director of the Colorado Forest Restoration Institute, is of a longer fire season, now beginning some years in March. Fires have been burning hotter. Even now, 15 years after the Hayman Fire of 2002, the largest fire in Colorado’s recorded history, which also occurred in the foothills southwest of Denver, lands have been slow to regenerate.

“This is not what we might have expected under historic fire regimes, indicating a likely loss of forest resilience,” he said. Some research suggests it will take the forest 900 years to regain its resilience, he added.

The event at which Cheng spoke featured both water providers and environmental organizations, all focused on the idea of creating partnerships for forest management. Most if not all concur with the idea that forests in key areas need to be thinned, to reduce risk of fire impacts to streams and rivers, after a century or more of fire suppression.

Cheng warned against expecting too much. “We can’t necessarily stop these types of fires, but we can influence the impacts,” he said.

A group of water providers and land management agencies called the Front Range Roundtable was formed to serve as a focal point for coalescing efforts to improve what is often called forest health. In other words, in most cases they want to thin forests.

In one such project, Denver Water in 2010 put in $16.5 million toward forest management, with that amount matched by the U.S. Forest Service and other state and federal agencies. Recently it renewed that commitment for another five-year run, with work planned for both Summit and Grand counties at the headwaters of the Colorado River. If located across the Continental Divide, Denver draws water from both places.

“You can’t treat everywhere,” said Cheng. “You have to be realistic about what you are trying to do.”

He also warned against expecting that fire can be stopped altogether. “There is no published paper that says that treatment will stop fire, you can’t stop fire. You can only modify fire behavior and the effects up to a certain point.”

If fire is natural on the landscape, and climate change, too, most of the climate change now underway is unnatural, the result of greenhouse gases and other human activities.

Jeff Lukas, a scientist from the Western Water Assessment in Boulder, Colo., outlined the evidence for rapid change: the last three years have been the warmest on record and, in Western states, the temperatures have increased 2 degrees Fahrenheit in the last three decades. Heat waves have been longer, and the same is true of frost-free season—no doubt a welcome respite in many mountain towns.

Snowmelt has come earlier. “Peak runoff is earlier virtually everywhere, and in particular in the more coastal regimes,” he said, referring to both the Sierra Nevada and to the Cascade Range.

But annual streamflow is declining in most areas, as more precipitation is lost to the atmosphere as a result of both evaporation and transpiration.

“The atmosphere giveth, and the atmosphere taketh away,” explained Lukas. This thirsty atmosphere is called the vapor-pressure deficit. What’s important is that the thirst that causes soil to dry out and streams to evaporate increases exponentially with temperature. Generally, the atmospheric thirst is projected to increase 10 to 25 percent by mid-century.

The upshot of this progression of warmth is more rain in place of snow, reduced late-summer flows, and more severe droughts. Droughts, in turn, stress trees leading to more vigorous insect infestations and disease outbreaks.

There’s also this: more frequent and destructive wildfires. And finally: over time, changes in the trees and plants you will see outside your mountain town window.

Lukas emphasized uncertainties. Climate models use different approaches, and although many concur in key predictions, there is no universal certainty. “Don’t let them give you just one number,” he said. “There should be a range.”

For example, the models concur about increased warming. There is high confidence of this. But there is a range of predictions about how much: 2.5 to 6.5 degrees Fahrenheit by 2050. Part of this depends upon to what extent the emissions of greenhouse gases can be slowed or even withdrawn from the atmosphere.

Physics of clouds continue to confound scientists. There is no clear understanding of how much increased water vapor—itself a greenhouse gas—in the atmosphere will in turn cause increased heating.

For that matter, it’s unclear whether warming temperatures will cause more or less precipitation. Most models suggest less moisture in places like Mammoth and Telluride, but with more precipitation in Ketchum, and almost certainly so in Canada. But again, this is likely to come increasingly as rain, not snow.

Climate models show warming as inevitable. Absent the moderating effects of a nearby ocean, Colorado and other states in the continent’s interior are expected to see temperatures rising more rapidly. It might already be happening, but the effect is not as obvious we might be expected, says Lukas.

Higher-elevation mountains are expected to warm even more as the snow gives way to bare ground for more of the year, which absorbs solar radiation instead of reflecting it, as snow does. This more rapid elevation gradient warming has been detected in the Himalayas, but there are too few high-quality temperature mountains in the mountains of Colorado to confirm it here.

Heat has a muscular effect among these changes. For example, If precipitation increases 100 percent but evaporation and transpiration increase 50 to 90 percent, that means 50 percent less runoff.

If drought obviously stresses trees, scientists remain unclear about the exact mechanisms by which trees die.

Further, not all forests turned red by bark beetles can be blamed solely on drought and warmer temperatures. But they have played a factor in the 40 million acres in western North America affected since the late1990s.

Frequency and scale of fires in the West has increased, owing to earlier snowmelt and drier fuels. One new study concludes that roughly 50 percent of the total burned area in the West since 1984 is due to climate change—a figure that Lukas said he doubts. Also, it’s important to remember that even bigger fires occurred naturally before the 1800s, when Euro-American settlers arrived. Fire is a component of the landscape.

But warming will produce changes. Trees will want to shift upslope or, more slowly, to more northerly latitudes For example, the Engelmann spruce and subalpine fire forests found today in Colorado at 10,000 feet might be replaced by lodgepole pine, and lodgepole might be replaced by ponderosa.

At least in Colorado, the vast majority of moisture falls in the form of snow in the elevation band of 9,000 to 11,000 feet, mostly spruce-fir forests. “We need to keep our eye on the spruce-fir zone in terms of watershed impacts.” said Lukas. “That’s where most of our water comes from in the West.”

PowerPoint slides courtesy of Jeff Lukas and Tony Cheng.

The Hutchins Water Center’s latest newsletter is hot off the presses

Click here to read the newsletter. Here’s an excerpt:

DOUBLE PEAK SNOWPACK MELTING

The amount of water in the Upper Colorado Basinwide snowpack peaked early, started to melt and then bumped back up, before dropping steeply again. Similar stories unfolded in the sub-basins, with the Upper Green and Duchesne groups showing the most impressive peaks and the Yampa/ White group the only one to post lower than average numbers. To see how the total accumulations by month add up in Colorado’s basins, choose the stacked bar option on this page.

Antarctic Surface Melt More Widespread Than Thought — @AndreaTWeather @ClimateCentral

From Climate Central (Andrea Thompson):

Since the days of the great early 20th century polar explorers, scientists have noticed the unbelievably bright blue ponds and streams of meltwater that can form on the glaciers and ice shelves of Antarctica and were even crucial to the recent collapse of one ice shelf.

While most research into Antarctic ice melt has concentrated on the impacts of warming ocean waters that are eating away at the ice from below, a new continent-wide survey shows that these surface meltwater drainage systems are much more prevalent around the continent than was previously thought.

Aspinall unit operations update

Aspinall Unit

From email from Reclamation (Erik Knight):

The April 15th forecast for the April – July unregulated inflow volume to Blue Mesa Reservoir is 850,000 acre-feet. This is 126% of the 30 year average. Snowpack in the Upper Gunnison Basin is currently 124% of average. Blue Mesa Reservoir current content is 623,000 acre-feet which is 75% of full. Current elevation is 7495.3 ft. Maximum content at Blue Mesa Reservoir is 829,500 acre-feet at an elevation of 7519.4 ft.

Black Canyon Water Right

The peak flow and shoulder flow components of the Black Canyon Water Right will be determined by the May 1 forecast of the April – July unregulated inflow volume to Blue Mesa Reservoir. If the May 1 forecast is equal to the current forecast of 850,000 acre-feet of runoff volume, the peak flow target will be equal to 6,427 cfs for a duration of 24 hours. The shoulder flow target will be 831 cfs, for the period between May 1 and July 25. The point of measurement of flows to satisfy the Black Canyon Water Right is the Gunnison River below Gunnison Tunnel streamgage at the upstream boundary of Black Canyon of the Gunnison National Park.

Aspinall Unit Operations ROD

Pursuant to the Aspinall Unit Operations Record of Decision (ROD), the peak flow and duration flow targets in the lower Gunnison River, as measured at the Whitewater gage, will be determined by the forecast of the April – July unregulated inflow volume to Blue Mesa Reservoir and the hydrologic year type. At the time of the spring operation, if the forecast is equal to the current forecast of 850,000 acre-feet of runoff volume, the hydrologic year type will be set as Moderately Wet. Under a Moderately Wet year the peak flow target will be 14,350 cfs and the duration target at this flow will be 10 days. The duration target for the half bankfull flow of 8,070 cfs will be 40 days.

Projected Spring Operations

During spring operations, releases from the Aspinall Unit will be made in an attempt to match the peak flow of the North Fork of the Gunnison River to maximize the potential of meeting the desired peak at the Whitewater gage, while simultaneously meeting the Black Canyon Water Right peak flow amount. The magnitude of release necessary to meet the desired peak at the Whitewater gage will be dependent on the flow contribution from the North Fork of the Gunnison River and other tributaries downstream from the Aspinall Unit. Current projections for spring peak operations show that flows in the Gunnison River through the Black Canyon could be over 9,000 cfs for 10 days in order to achieve the desired peak flow and duration at Whitewater. If actual flows on the North Fork of the Gunnison River are less than currently projected, flows through the Black Canyon could be even higher. With this runoff forecast and corresponding downstream targets, Blue Mesa Reservoir is currently projected to fill to an elevation of around 7507 feet with an approximate peak content of 719,000 acre-feet.

#Runoff news: McPhee scheduled releases into Dolores River

Dolores River near Bedrock

From CanoeKayak.com (Eugene Buchanan):

The Dolores River Monitoring and Recommendation team recently agreed on a plan to release water from the dam, which involved input from water managers, boaters, scientists, environmental groups, federal lands agencies, and local governments.

Surplus water is expected to spill from the McPhee Dam from April 13 until mid-June, with 45 to 60 days of flow planned at 2,000 cubic feet per second. Water managers plan to release an even larger burst of water, expected at 4,000 cfs, during three days in late May (May 19-22). Scientists say the extra water will flush extra sediment downstream and create better habitat for native fish.

“That’s a great flow level, something we haven’t seen in years,” says local rafter Sean McNamara. “Bring on Snaggletooth!”

Despite the extra water, water managers say all water allocations will be met, including those for agricultural use.

Waldo Canyon burn scar still a flash flood threat after five years

Waldo Canyon Fire burn scar

From KOAA.com (Lena Howland):

In order to mitigate the risk, the city has been working on a number of stormwater projects along North Douglas Creek, South Douglas Creek and Camp Creek, all runoff areas from the burn scar.

“We have not let our guard down, ever since the Waldo Canyon Fire, we’ve had so many opportunities to do repairs and projects in order to prevent any more damage coming from the burn scar, as much as practical,” Kelley said.

All lessons learned, Kelley says they are more prepared to handle flash floods now than they were five years ago.

“We have an operations and maintenance division which responds on the spot to any types of flooding concerns, our emergency operations center is fully functioning and everybody is prepared for this type of an event to occur,” he said.

The City of Colorado Springs has created an Emergency Preparedness Manual for everyone which can be found here.