If we are to plan for the future of Utah’s water supply, it is important to understand what that future is expected to bring. Relying on past hydrologic conditions and expecting that regime to be our future is folly.
The hydrology of the Western U.S. is changing. We’re experiencing drier, hotter conditions and more stagnant weather patterns. These changes are upon us now, and are projected to become even greater in the not-too-distant future. As such, do we proceed with this in mind, or do we look to the past and hope this will be our future. Our children and grandchildren will judge us for what we do now.
The Colorado River Basin receives the majority of its precipitation in the form of snowfall during the meteorologic winter (December, January and February). However, what used to be primarily snowfall during the winter is shifting to increased rainfall during that same time. In essence, we are evolving from primary a snow-driven hydrology to that of a rain-driven hydrology near the end of the century. We’re seeing this change now. Data has shown that winters are starting later, and ending earlier, throughout the Colorado, Green and Great Basins. But why?
The answer comes in two forms. The desert Southwest is warming faster than the global average, and is expected to warm an additional 8 degrees to 10 degrees Fahrenheit by 2100. As such, we’re experiencing more rainfall during the winter months than we used to. The actual window of snow accumulation is shrinking as we warm.
Winters start later, and end earlier. Premature melting of our snowpack due to this warming produces inefficient runoff scenarios, where we lose more to evaporation, transportation and sublimation. Research has shown that our snowpacks through the Western U.S. will be reduced by 80% by 2100. And with that, the way we receive our precipitation is changing. Storms are less frequent, and more intense, making storage an issue.
Additionally, the presence of high pressure ridging is dominating our weather pattern during the winter months. This weather pattern is characterized by the lack of storms, low snowpacks and inversions. The incidence of high pressure ridging over the West has been increasing since about 1980. This is due to the slowing of the Jet Stream, making weather patterns more stagnant across the globe. Research has shown that the increased incidence of high pressure dominating our winters across Western U.S. will steadily increase bringing less winter precipitation, drier soil moistures and reduced snowpacks.
The two combined factors of stagnant dry weather, and an overall warmer climate does not bode well for our water picture throughout Utah and the West. With this scenario in our future, we must plan for reduced river flows along the Colorado, Green and Great Basin watersheds, which will jeopardize future development projects such as the Lake Powell Pipeline.
We cannot look to the past and assume this is our future. With the mountain of research telling us that Utah and the Colorado Basin will be much hotter and drier, should we proceed with the idea that what once was will be our future? It is important we prudently plan with conservation in the forefront of our thought process and allocate wisely.
Brian McInerney
Brian McInerney, Park City, is co-director of the Utah Climate Project.