It’s no secret that Glacier National Park’s namesake glaciers are disappearing, posing potential problems on both sides of the Continental Divide for those dependent on meltwater during Montana’s dry summers.

But for the first time, a peer-reviewed scientific study scheduled for publication in the next couple of weeks will present a model quantifying the contribution of the park’s 39 named glaciers to local watersheds.

The study will be published in the University of Colorado’s Arctic, Antarctic and Alpine Research journal.

The research effort began about five years ago with Whitefish native Adam Clark’s graduate thesis at the University of Montana Geosciences Department, where he studied under another one of the study’s coauthors, Joel Harper. Now Clark works for the U.S. Geological Service’s Northern Rocky Mountains Science Center with Dan Fagre, the other coauthor of the study.

“There have been a few studies measuring melt at a handful of other glaciers over the years, but as far as calculating a number from all the glaciers in the park, this is new,” Clark said.

Glacier Park is home to the second-highest concentration of glaciers in the U.S. Rocky Mountains, but the total glacial coverage in the park has declined by 35 percent in the last half-century as an increasingly warm atmosphere outpaces the rate at which new precipitation allows glaciers to grow.

Historically, the water melting from the glaciers each summer has provided some stability to both the temperature and the flow of water upon which many downstream irrigators depend.

According to the study, the Flathead River will see distinctly lower impacts in overall flows compared with waterways east of the Continental Divide, where about two-thirds of the park’s total glacial melt flows.

Researchers estimate a gauge on the North Fork of the Flathead River 34 miles downstream from the nearest glacier had glacial melt contributing about 6.3 percent of total August flow in 2009 and about 5 percent in August 2010.

For a gauge on the Middle Fork 21 miles downstream from the nearest glacier, those numbers were 7.5 percent and 6.3 percent.

For the St. Mary River on the east side, a gauge 19 miles downstream showed as much as 12.7 percent of the flow originating from glacial melt in August 2009 and 8.9 percent in 2010.

The report notes that downstream irrigation uses removed an average of 69 percent of the St. Mary River’s discharge 1.2 miles below the gauge during the month of August between 2000 and 2010.

Clark and his coauthors noted their calculations did not take into account several factors, such as evaporation and loss to groundwater along the way, that likely lower the overall contribution of glaciers to downstream flows, meaning the numbers from their models are maximums.

The study concedes some other limitations, most notably variations in temperature.

Clark said he calculated the maximum possible error for temperature readings, resulting in a potential change to 2009’s glacial runoff totals of 24 percent and up to 19 percent for 2010.

However, the study notes the likelihood that such errors would happen on the warmer and colder ends of the spectrum, resulting in a “cancellation effect” in the model. The authors conclude by saying, “[b]ased on comparisons to independent measurements of glacial surface melt and glacial outlet stream runoff, we argue that this model is an effective and reliable tool for estimating glacier-derived runoff.”

Obtaining the data was no easy task. Measurements of glaciers and their changing conditions over time are hard to come by owing to their remoteness. Researchers set up temporary weather stations on glaciers in the park, chosen for their representative characteristics of the larger glacial area.

“In 2010, it occupied my entire summer. It was a lot of work,” Clark said. “Each glacier had a weather station installed on it and I had to hire people to help carry stuff up there with me … It took about a month to get all the weather stations set up, and by the time I finished up it was time to go back and check” on the recording at the first weather station.

Each weather station was hand-built from seventeen 4-foot poles carried up into the mountains, fastened together to make a tripod. The researchers then drilled 22 feet into the tops of the glaciers, hanging a range of solar-powered instruments from the crossbars to measure temperature, solar radiation and the lowering of the glacier’s surface.

As the ice melted during the summer, the crossbars had to be manually lowered to keep the structure from getting too top-heavy. The measurement period went from June through September.

Compared with the expected impacts to irrigators, many of the high-altitude plants and animals that depend on the park’s unique ecosystem are at much higher risk.

The study singles out the meltwater stonefly, an insect found only in the cold-water streams of Glacier Park, within 500 meters of the melting snow and ice. Bull trout, a federally threatened species native to the Flathead Lake ecosystem, are also dependent on relatively cold water, and the loss of summer glacial melt would be just one more of several environmental stressors the fish already face.

Fagre, a research ecologist, coauthored the study with Clark and has spent decades studying the park’s glaciers and the organisms that depend on them. As global temperatures continue to climb, he said the effects of a shorter snow season and less snowmelt overall will have more substantial effects to those downstream than just glacial melt.

“The disappearance of the glaciers will clearly have an impact on the biota adapted to high elevations and the central core parts of Glacier National Park,” Fagre said. “They are also harbingers for the kind of effects that disappearing snow will have, that are much broader across the landscape than just the glaciers.”

Meltwater estimates from nonglacial snow and ice was not included in the study. Above 6,500 feet (the elevation of Logan Pass), those sources of runoff can persist until July.

Extrapolating those numbers to a meaningful prediction of overall water levels for downstream users will require more research, however.

“I think it’s a good place to start — it’s a good baseline,” Clark said. “I believe it did a good job quantifying glacier melt rates, but my comparison was simply adding up the total water melting off a glacier and comparing it to a stream gauge, which is very limiting since we don’t have many stream gauges.”

He said he hopes future studies by hydrologists will be able to fill in the gaps and understand how the glacial meltwater actually moves through the system.

Reporter Samuel Wilson can be reached at 758-4407 or by email at swilson@dailyinterlake.com