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Snow water resource impacts shared

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The Wyoming Water Forum, hosted by the Wyoming State Engineer’s Office, welcomed United States Geological Survey (USGS) Physical Scientist with the Wyoming-Montana Water Science Center Theodore Barnhart in the Oct. 13 forum. Barnhart works to improve hydrologic predictions and further the understanding of mountain hydrology along with the distribution and variability of snowpack. 

“Snow water resources are extremely important and valued at trillions of dollars globally,” says Barnhart. “A lot of precipitation comes as snow and is stored for future use, so it is really important to understand mountain snowpack and how it is changing.” 

Influence of snowmelt

Barnhart’s presentation focused on changing snowmelt and land cover and how implications from these changes affect water availability and hydrologic modeling. At a plot-sized scale, Barnhart’s research worked to answer how changes in snowmelt influence runoff and streamflow production. 

“High snowpacks tend to melt later in the season and quickly, while low snowpacks melt early and slow,” explains Barnhart.

The study utilized data from the Niwot Ridge eddy covariance tower in Colorado and the Providence Creek eddy covariance tower in California. Barnhart used a hydrological model to simulate evapotranspiration, subsurface water drainage, plant available moisture and to simulate snow accumulation and melt. 

“Plants don’t have the energy to start using melt water early in the season, sending more water down the watershed,” Barnhart shares as an implication of low snowpack levels found in his study. “More rapid snowmelt increases runoff, while later snowmelt decreases runoff.” 

Barnhart explains the runoff increase from early snowmelt has the potential to offset streamflow decreases due to slower snowmelt. 

Land cover impacts

Using a landscape disturbance and succession model called LANDIS-II, Barnhart evaluated land cover evolution, aboveground biomass and species-age distribution to answer the question of how future changes in land cover, air temperature and precipitation impact streamflow. This study was completed at the catchment scale using Como Creek, which drains off of Niwot Ridge near Boulder, Colo. 

“We saw a forested area increase from 72 percent to 95 percent. Effective precipitation increased by 17 to 19 percent,” explains Barnhart. “The runoff ratio also increased by nine percent to 18 percent by the year 2100.”

Evaporation increases in the future due to a warming-induced increase in the vapor pressure deficit while transpiration decreases, says Barnhart. This results in a decrease of net evapotranspiration, mostly because of early snowmelt, and subsequent water delivery happens before plants can utilize the water. 

“Land cover change in alpine catchments may lead to increased, instead of decreased, streamflow in the future,” says Barnhart. “Again, we see more rapid snowmelt tends to increase runoff.” 

Regional runoff  

Previous research Barnhart used to inform his studies shows snowier basins tend to over-produce streamflow and the shift from snow to rain results in less streamflow. At the regional scale, Barnhart discusses research looking to see if snowmelt rate controls the relative hydrologic partitioning of snowmelt and evapotranspiration. 

“The southern Rockies see the greatest streamflow sensitivity to changes in snowmelt rate, while the northern Rockies are the least sensitive,” Barnhart notes. “Rapid snowmelt also leads to increased baseflow and streamflow production across the western U.S.” 

“Different regions have different streamflow production, suggesting water management needs to be different in certain areas,” continues Barnhart. “This kind of work often creates more questions than it answers.” 

In relevance to Wyoming, Barnhart says this research has many potential uses to identify areas where snowpack melt and timing might be changing and could potentially help to identify seasonal water availability forecasting. The work could also potentially create better snow-vegetation interactions in windy, high-elevation environments. 

Averi Hales is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.

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