BILLINGS – Since 1948, the Greater Yellowstone Area has consistently warmed, especially in the winter and summer months, according to a recently released U.S. Geological Survey study.

Using an algorithm developed at the University of Montana, Adam Sepulveda, a research zoologist at the Northern Rocky Mountain Science Center in Bozeman, calculated temperatures at 50 different sites within the GYA between 1948 and 2012 at different elevations and with varied sun exposure to look for patterns. The study appears in the latest issue of the journal Plos One.

Given the warming trend, Sepulveda said “the most recognized threat” to the region is the possibility of less snowfall.

“Our data show us that winter is warming the fastest, and particularly March,” he said, which is the primary snow-producing month in the GYA.

Steve Running, a regents professor of ecology at the University of Montana, whose department developed the algorithm Sepulveda used, said “our biggest temperature changes (around the Northern Rockies) are in the winter months.”

“Whereas 40 to 50 below zero used to be common in the winter, now it’s 20 to 30 below, which still sounds cold, but that’s a lot warmer,” Running said.

The impact of that climate change could eventually be dramatic – and not just for the Greater Yellowstone Area.

“The warming winter temperatures in the GYA are of large concern because the majority of surface water in this region originates as mountain snowpack,” Sepulveda wrote. “These surface waters feed three major rivers that provide critical societal and environmental services: the Snake-Columbia, the Green-Colorado, and the Yellowstone-Missouri rivers. Increases in winter and spring temperatures in the West result in less snow accumulation in the winter and earlier timing of water released from the snowpack, which affect the timing of water delivery to downstream irrigation users, municipalities, and hydropower production facilities and influence recreational water uses (e.g., angling and boating) in gateway and downstream communities.”

As regions go, the varied elevations and terrain of the GYA will help armor it somewhat against that gradual change.

“It has the potential to be more resilient at least to extremes,” Sepulveda said, “because it’s a larger area with topographic and climate variability.”

“Think of the diversity of habitat in an Iowa cornfield, you have one,” Running explained. “In Yellowstone, you have a mixture of habitats that gives the whole ecosystem more resilience.”

Yet even with those protections, warm areas will get warmer and so will cool areas. That means crowding some species like amphibians into a shrinking number of cool, wet areas. As that variety in habitat is lessened, so too are species likely to be trimmed.

“This idea that diversity produces stability tends to be a very important maxim for many things, including conservation,” Sepulveda said.

The GYA is a 34,000-square-mile ecosystem that crosses the corners of three states: Montana, Wyoming and Idaho. It’s the largest protected reserve in the lower 48 states and therefore home to robust populations of large mammals like bison, grizzly bears and elk. At the center of the ecosystem is Yellowstone National Park, a protected reserve for those species.

For Yellowstone scientists, the greatest concerns from a warming climate include: changes in the composition of plants and animals; altering the amount and timing of spring snowmelt, which affects water levels, vegetation growth and the movement of wildlife from migrating bison to spawning trout to the arrival of pollinators; and fire frequency and season length could increase, according to the park’s website.

Sepulveda said he and his collaborators on the study worked hard to “not pitch the worst-case scenario,” so there is the potential – depending on how humans respond to an increasingly warmer climate – for the climate to be “warmer or worse, based on your perspective.”

“It’s really hard to figure out how warm things will get,” Sepulveda said. “The important thing, though, is that no matter what projections you look at things are progressively warming.”

Brett French can be reached at bfrench@billingsgazette.com.

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