The University of Colorado at Boulder has been awarded $1.4 million for a new study on how changes in land use, forest management and climate may affect trans-basin water diversions in Colorado and other semi-arid regions in the western United States.

The grant, part of the National Science Foundation-U.S. Department of Agriculture Water Sustainability Climate Program, was awarded to Assistant Professor Noah Molotch of the geography department. Molotch and his team will be identifying thresholds, or “tipping points,” of change in land use, forest management and climate that may compromise the sustainability of the policies and procedures that dictate the timing and quality of water diverted from Colorado’s West Slope to the Front Range.

Molotch said that in Colorado and semi-arid regions around the world, trans-basin water diversions that redirect water from areas of surplus to areas of demand are based on policy agreements and infrastructure operations made under climatic and land use conditions that may differ considerably from conditions in the near future. Measurements over the past 50 years, for example, suggest a broad-scale reduction in snowpack water storage in the western U.S. because of regional warming temperatures, a trend due in part to a shift from snowfall to rainfall, he said.

The Colorado Big Thompson Project depends upon a dwindling supply of Western Slope snowpack.

In addition, land-cover changes associated with population growth, fire suppression and mountain pine beetle outbreaks have altered the hydrology of mid-mountain ecosystems in the West, said Molotch, who also is a scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. CU is teaming up with the National Center for Atmospheric Research in Boulder on the NSF-funded project.

The NSF award comes on the heels of a May 2012 agreement between water managers in Summit and Grand counties on Colorado’s West Slope and in the Denver area on how best to share water from the Colorado River basin. “This is a great example of communities that historically battled for water resources coming to the table in a good faith effort to find solutions to water allocation issues,” said Molotch. “These groups have no pretenses about the potential impacts of climate change and realize we can’t afford to bury our heads in the sand on this issue.”

Collaborators on the project include Patrick Bourgeron and Mark Williams, fellows at CU-Boulder’s Institute of Arctic and Alpine Research, and David Gochis, Kathleen Miller and David Yates of NCAR.

A study led by Molotch published Sept. 10 in Nature Geoscience tied forest “greenness” in the western United States to fluctuating year-to-year snowpack.  The study indicated mid-elevation mountain ecosystems — where people increasing are building second homes and participating in a myriad of outdoor recreational activities — are most sensitive to rising temperatures and changes in precipitation and snowmelt.

“We found that mid-elevation forests show a dramatic sensitivity to snow that fell the previous winter in terms of accumulation and subsequent melt,” said Molotch, also a fellow at INSTAAR. “If snowpack declines, forests become more stressed, which can lead to ecological changes that include alterations in the distribution and abundance of plant and animal species as well as vulnerability to perturbations like fire and beetle kill.”

Colorado snowpack was at an all time low this past winter

As part of the new award, Molotch and his team will evaluate regional climate models in the mountain West developed at NCAR in an attempt to make temperature, precipitation and snowpack projections “more robust,” Molotch said. While the efficiency of water in trans-basin diversion projects in the western U.S. has in the past been enhanced by the natural storage of moisture in mountain snowpack that allowed for a slow, steady delivery of water into the system, warming temperatures are already causing this beneficial “drip effect” to be greatly reduced, he said.

If the winter temperatures are hovering around 15 degrees Fahrenheit and the climate warms by a few degrees, for example, there will be negligible impact on snowpack, Molotch said.  But if temperatures hover near freezing, slight temperature increases can trigger earlier snowmelt, and precipitation that used to be in the form of snow turns to rain, significantly affecting trans-basin water diversion activities.

“One of the most interesting aspects of this project to me is the changes we are seeing in the ‘wildland-urban interface,’ particularly in Colorado,” he said.  “There is some irony that Front Range people who have built second homes in Summit County, for example, may actually start to have an effect on the water they have relied on to be piped through the Continental Divide to the Denver area.”

Burned forests can cause early runoff

In addition to providing land and water resource decision makers with projections on how future water supply and demand will change in the future, the NSF-funded project will provide a unique educational experience for graduate students, Molotch said.

“We have climate change, snowpack, changes in land use, all feeding into the pipeline that is bringing water to Colorado’s Front Range,” he said. “As the two main stressors, climate change and land use increase, there is the possibility of pushing the systems into an unsustainable state.”