Rising temperatures threaten Salt Lake City’s water supply

analysis — which creeks are likely to be impacted most and soonest, how water sources on the nearby western flank of the Wasatch Mountains and the more distant eastern flank will fare — are critical to water managers with Salt Lake City.

“We are using the findings of this sensitivity analysis to better understand the range of impacts we might experience under climate change scenarios,” said co-author Laura Briefer, water resources manager at the Salt Lake City Department of Public Utilities. “This is the kind of tool we need to help us adapt to a changing climate, anticipate future changes and make sound water-resource decisions.”

“Water emanating from our local Wasatch Mountains is the lifeblood of the Salt Lake Valley, and is vulnerable to the projected changes in climate,” said Salt Lake City Mayor Ralph Becker. “This study, along with other climate adaptation work Salt Lake City is doing, helps us plan to be a more resilient community in a time of climate change.”

Among the details in the new assessment:

• Temperatures are already rising in northern Utah, about 2 degrees Fahrenheit in the last century, and continue to climb. Summer temperatures have increased especially steeply and are expected to continue to do so. Increasing temperatures during the summer irrigation season may increase water demand.
• Every increase in a degree Fahrenheit means an average decrease of 3.8 percent in annual water flow from watersheds used by Salt Lake City. This means less water available from Salt Lake City’s watersheds in the future.
• Lower-elevation streams are more sensitive to increasing temperatures, especially from May through September, and city water experts may need to rely on less-sensitive, higher-elevation sources in late summer, or more water storage.
• Models tell an uncertain story about total future precipitation in the region, primarily because Utah is on the boundary of the Southwest (projected to dry) and the U.S. northern tier states (projected to get wetter).
• Overall, models suggest increased winter flows, when water demand is lower, and decreased summer flows when water demand peaks.
• Annual precipitation would need to increase by about 10 percent to counteract the stream-drying effect of a 5-degree increase in temperature.
• A 5-degree temperature increase would also mean that peak water flow in the western Wasatch creeks would occur two to four weeks earlier in the summer than it does today. This earlier stream runoff will make it more difficult to meet water demand as the summer irrigation season progresses.

Earth Interactions is jointly published by the American Geophysical Union, the American Meteorological Society, and the Association of American Geographers.

CIRES is a joint institute of NOAA and CU-Boulder.

— Read more in Tim Bardsley et al., “Planning for an Uncertain Future: Climate Change Sensitivity Assessment toward Adaptation Planning for Public Water Supply,” Earth Interact 17 (October 2013): 1–26 (doi: http://dx.doi.org/10.1175/2012EI000501.1)