Warmer climate, less water for Salt Lake City
Climate change • Temperature increase is expected to cut the annual flow from watersheds tapped by Utah's capital city.
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Research on climate change typically focuses on massive and sensitive landscapes across the globe.

A new study released Friday took a look at a tiny but important — at least for Salt Lake City residents — portion of the planet and the impact warming temperatures will have on a key resource for the population: water.

"Our concern is that it is going to get warmer in the Intermountain West and in our particular region," said Laura Briefer, water resources manager for the Salt Lake City Department of Public Utilities. "As water managers, a warming climate demands our attention. We anticipate changes to water demands and supply."

Among the most telling results of the report is a finding that every 1 degree Fahrenheit increase could mean an average decrease of 3.8 percent in annual water flow from watersheds tapped by Salt Lake City.

That's according to the study "Planning for an Uncertain Future: Climate Change Sensitivity Assessment Toward Adaptation Planning for Public Water Supply," published in the journal Earth Interactions.

The lead author on the project was Tim Bardsley, the Utah liaison and hydrologist for Western Water Assessment through the National Oceanic and Atmospheric Administration's Cooperative Institute for Research in Environmental Studies at the University of Colorado Boulder.

A large portion of Salt Lake City's water supply — 50 percent to 60 percent — comes from four Wasatch Front streams: City Creek, Parleys Creek and Big and Little Cottonwood creeks. Those streams, federal water storage reservoirs and deep wells provide Salt Lake City's water.

"We focused on those four creeks because they are a primary supply that runs right into the city," Bardsley said. "It is the timing of stream flow that is of particular importance to Salt Lake City."

Warmer temperatures mean more winter precipitation will fall as rain rather than snow, increasing flows at a time when demand for water is at its lowest. The current infrastructure used by Salt Lake City, which serves more than 349,000 people, is based on tracking snowpack and runoff and then balancing the water the system can hold against other options such as Deer Creek Reservoir through the Central Utah Project.

The study also shows a 5-degree temperature increase would send the peak water flow two to four weeks earlier than it currently happens. Only a 10 percent increase in annual precipitation could counteract a 5-degree increase in temperature.

"We don't see a whole lot of new places for surface storage of water," Briefer said. "We are experimenting with, and looking at, aquifer storage."

The study used pioneer historical weather records to create some of the models, but the researchers went even further into the past to identify possible scenarios. They studied tree rings in the watershed to examine past extreme droughts, Bardsley said.

"While the observed droughts were extreme, even in the context of the 600-year period, the tree-ring record indicated there have been droughts of greater intensity or duration," he said. "What we found is that temperature increases could produce short- and long-term droughts well beyond any severity in the observed tree-ring records."

Another way to stretch water resources is by conservation. Briefer said Salt Lake City residents are doing a good job conserving water, but that there is always more that can be done.

"They have been very responsive to our water conservation messaging, education and pricing incentives," she said. "That doesn't mean there isn't room for improvement."

While the study was focused on Salt Lake City, Briefer said other cities and communities can learn a lot from the report.

"We looked specifically at the Salt Lake water system, but there are implications throughout Salt Lake County and possibly Utah County," she said. "There are things from the report that can help serve communities throughout the West."

Bardsley complimented Salt Lake City for being ahead of the game when it comes to pondering ways to maintain and provide a resource as important as water.

"Salt Lake has a lot going for it. Looking at the issues ahead of time is a practical way of thinking about it," said Bardsley, who indicated the studies started with this project will continue. "They have been leaders in evaluating potential challenges to the future supply of water and they are an example for other utilities to follow."

brettp@sltrib.com

Twitter: @BrettPrettyman