Disappearing glaciers: precip, not temp
Although the remote glaciers of Wyoming’s Wind River Range may never be seen by most in the ag community, they tie directly to agriculture as a steady supply of late-season streamflow and irrigation water.
Since 2006 a study funded by the Wyoming Legislature and administered by the Wyoming Water Development Commission at the University of Wyoming has measured the glaciers to compare their present mass to that in the past and to determine how that translates to acre-feet of water down below.
Greg Kerr, who directs the UW Office of Water Programs, leads the project.
“The Wyoming Water Development requested we look at what kind of streamflow contribution we’re getting from the glaciers,” says Kerr, adding they wanted the information for future water planning in the river basins. “Glaciers provide a stable source of water with less variability in the hydrograph for their watersheds.”
He says heavily glaciated watersheds have been documented to provide more water runoff, and more water later in the season.
For the study the UW team focused on Dinwoody Glacier because of previous records taken in 1988 and 1989, as well as 2006. The team took general observations of the glacier through a GPS survey and radar measurements to record ice thickness. Horses packed in the team’s equipment to within three miles of the glacier, and because of environmental and recreational restrictions the graduate students packed the gear the rest of the way.
“We started with GPS mapping of the surface area and the radar measurements, which are similar to riding around in a boat on a lake,” says Kerr. The measurements were taken in a grid system to compare to 1989 measurements.
The team also repeated ground photography to track visual change in the glaciers.
“There’s not any surprise the ice is melting, and there are pretty drastic changes,” says Kerr. “Now we have numbers to determine how much is gone, though it’s a time consuming process to come up with changes in the amount of surface area and the losses we find.”
From 1966 streamflow measurements to the 1989 and 2006 measurements, Kerr says in terms of acre-feet all the watersheds connected to glaciers are declining.
“From 1966 to 2006 the Dinwoody drainage lost about 205,000 acre-feet, while the Bull Lake creek lost 171,000 acre-feet and the Green River drainage lost 97,000 acre-feet,” says Kerr, comparing that to Alcova Reservoir at 168,000 acre-feet. “We’ve lost an equivalent above what we have in the storage of Alcova.”
Traditionally ice melt from Dinwoody has contributed seven percent of runoff to the Dinwoody Creek, three percent to the Bull Lake Creek watershed and one percent to the Green River in early summer.
Shifting to late summer, however, in July through September the flows from 1989 through 2006 have contributed 13 percent to Dinwoody Creek, seven percent to Bull Lake and three percent to the Green River.
“In late season the contribution to flow is increased considerably, delaying the seasonal hydrograph,” says Kerr.
Compairing the Bull Lake watershed with the non-glaciated Wind River watershed, Kerr says 44 percent of annual streamflow comes down between July and September in the Bull Lake area, while only 26 percent comes down in that time period for the Wind River drainage.
“That confirms glaciers contribution and what they’re doing for us,” says Kerr.
In addition to measuring the ice mass, Kerr says he wanted to look at the influence of climate on the Green River Basin and the Wind River and Big Horn basin hydrology.
“I wanted to analyze the El Nino and La Nina affects on snowpack in the Wind River Range,” he says, “There are four other years that El Nino has lined up the same as it did this year, and three of those four showed below normal snowpack, and we’re seeing that so far this year.”
“What is climate change?” asks Kerr. “We hear the terms ‘climate change,’ ‘global warming’ and ‘climate variability. I see publications that say we’re going to start climate change, like a switch has been flipped, and everything has been on an even basis until now.”
“When we started this project, it was global warming that was melting the glaciers. I don’t say I disagree with that, but is it temperature that’s melting these glaciers?” he asks. “”The total volume of ice melt in acre-feet from 1966 to 1988 and from 1989 through 2006 has increased, although the temperatures have dropped on an annual basis. How do we have an increase in ice melt when we have annual temperatures that have decreased?”
Kerr proposes the root cause is precipitation. “It’s not the temperature that’s driven glaciers to melt. They’re starving to death. They don’t have the precipitation and snowpack covering them up, allowing them to build like they have in the past.”
Kerr says temperature takes over in melting the ice after the low snowpack leaves. “I don’t believe it’s driven by the temperature, but rather by the snowpack – just what we’re seeing this year.”
Another aspect of the study is reconstruction of hydrologic and climate records through tree ring studies and lake bogs. “Bogs can go back farther in the record than tree rings and determine more information from sediments than reconstructed streamflow and tree rings,” says Kerr.
“Droughts in those records lasted for years compared to what we’re in now. Climate change? It looks like it’s been around a long time. More severe? Definitely,” says Kerr.
“The volume of water lost through ice melt is significant,” says Kerr. “It’s equivalent to losing one of our large reservoirs, and it’s harder to get them back. Glaciers go through cycles, and they haven’t been here forever.”
Regarding the reconstructed precipitation and climate records, and “megadroughts,” Kerr says, “I hope history doesn’t repeat itself.”