In many Western cities, municipal water management is a job tied to the mountains. In Salt Lake City, for example, 80 percent of the city’s water supply comes from snowpack in seven Uinta and Wasatch Mountain watersheds.
Yet it’s becoming all too clear that the mountains’ water yield will decrease, come earlier in the year, or both. Cities and local water managers across the West – not just researchers looking at regional trends – are now trying to address those shifts. “We’ve observed changes in the climate in Salt Lake, and around the region, and it’s appropriate to think about how climate change is going to impact water supply,” says Tim Bardsley, a Salt Lake City-based hydrologist with the Western Water Assessment.
In the past, water resources managers could look at historical data and use that to make decisions about the future. Now that the future will surely look vastly different from the past, that approach is no longer valid.
But even as climatologists have provided climate predictions, they haven't been specific enough for many local water managers. For example, regional-scale research already portrays a warmer Intermountain West where more precipitation will fall as rain rather than snow, runoff will peak earlier, and streams will carry less water by late summer and fall. But because of how global climate models average data over large regions, they have painted with too broad a brush to be considered useful for the specifics of local water planning.
This is changing as finer scale climate data have become more readily available. Plus, local water managers and scientists are working in tandem to identify risks to water systems, and to create water plans that will work within a range of climate scenarios. Acknowledging the increasing demands on local leaders to deal with this global issue, and their prominence as problem-solvers (see the book “If Mayors Ruled the World”), President Obama issued an executive order last week on climate preparedness, focusing on state, city and county governments. As a nod to Salt Lake City Mayor Ralph Becker’s progressive sustainability agenda, he was selected for Obama’s climate adaptation task force.
Over the last few years, Salt Lake City’s public utilities department has been teaming up with climate scientists and hydrologists to analyze the Wasatch Front water supply’s sensitivity to climate change. In a study published last week in the journal Earth Interactions, Laura Briefer, water resources manager of Salt Lake City’s utilities department, her colleagues at the department, along with Bardsley, scientists from Boulder’s National Center for Atmospheric Research, and the National Oceanic and Atmospheric Administration, identified specific ways warmer temperatures will affect the city’s water supply.
They found that annual flow from Salt Lake City’s watersheds would decrease, on average, by 3.8 percent for every degree Fahrenheit in temperature increase. (The study predicts a temperature increase in the range of 1 to 6 degrees by the years 2035 to 2064.)
They also identified important changes in snowmelt timing. Big Cottonwood, Little Cottonwood, Parleys and City Creeks are important to watch because they supply 60 to 70 percent of Salt Lake City’s water. The utility relies on them in early summer before turning to water from federal reservoir projects to meet later season demand. But in the future, runoff from those creeks won’t be available for quite as long. That means the city would have to tap into stored water earlier, and put more pressure on their reserves. At Big Cottonwood Creek each degree of warming would shift the runoff season to start three days earlier, on average.
Climate change is going to shift the demand for water too, something the researchers are just starting to dig into. Even with population growth, total water use in the Salt Lake area has remained relatively steady over 30 years. But outdoor watering is still 45 percent of annual water use in Salt Lake City. In the future, warmer temperatures could increase that demand in late summer and fall, just as water supplies are dropping off for the season, creating a one-two punch for city’s water supply.
The first obvious solution to these problems would be more water conservation, which Salt Lake planners are hoping to increase with their current program. In the longer term, the city may look for new ways to capture spring snowmelt as it flows down the creeks earlier in the year. Dams won’t be an option since there really aren’t places to put them in those watersheds, says Briefer. Instead, Salt Lake City may consider injecting water into the aquifer and recovering it later. Like other cities, they’re also looking at reclaiming water from sewage treatment plants.
Along with all of this new climate-oriented water planning, Salt Lake is also trying to reduce its greenhouse gas emissions. Briefer says it's important to keep in mind how much energy any new water development strategy might use. “For every adaptation technique, one of the things that we’re doing is making sure we’re looking at it from a holistic perspective,” she says. “Are they strategies that cause other problems, or are they strategies that create opportunity?”
Sarah Jane Keller is an editorial fellow at High Country News. She Tweets @sjanekeller.