Basal flow is the movement of groundwater through streams and, on average, accounts for over 50% of annual flow in the upper Colorado River basin. It is vital for maintaining Colorado River flows during dry periods. Scientists from the US Geological Survey and the Bureau of Reclamation modeled the temperature, precipitation and runoff data to better understand how base flow may change in three future climate scenarios.
“Many studies project the response of flow and runoff to climate change in the upper Colorado River basin, but this is the first to examine the base flow component of total flow,” the hydrologist said. USGS Olivia Miller, lead author of the article. âUnderstanding how baseflow may respond to climate change is particularly important for water managers when it comes to ensuring an adequate water supply outside the spring runoff period and has critical implications for ecosystem health. “
The upper Colorado River basin has a drainage area of ââapproximately 114,000 square miles, covering parts of Colorado, Wyoming, Utah, Arizona, and New Mexico. The Continental Divide marks the eastern boundary of the basin while the western boundary is defined by the Wasatch Mountains. The Wind River and the Wyoming Ranges form the northern border and the southern portion includes the San Juan Basin. From 1984 to 2012, total river flow deliveries from the Upper Basin Outfall at Lees Ferry, Ariz. To the Lower Colorado River Basin averaged 10.3 million acre feet / yr (maf / yr) . The basic flow represented nearly a third (2.8 maf / year).
The study predicts that basal flow deliveries to the Lower Colorado River Basin may decline overall by the end of the 21st century despite potential increases in precipitation and basal flow in some areas. Three climate scenarios were modeled: in a hot and humid scenario, the total base flow at Lees Ferry is expected to initially increase to 6% (0.162 maf / year) in the 2030s, then stabilize in the 2050s and finally decrease by 3% from current levels (0.089 maf / year) by the 2080s. In a hot and dry climate scenario, base flow is expected to decrease to 23% (0.657 maf / year) in the 2030s and continue to worsen over time, reaching 29% (0.835 maf / year) in the 2050s and 33% (0.940 maf / year) in the 2080s. An intermediate climate scenario also showed a steady decline over the years. time.
The study authors hypothesize that base flow declines would occur due to increased water loss from streams due to processes such as evapotranspiration. The largest declines in the model occur in the Rocky Mountains and the upper Green River.
Declines in base flow have major downstream and basin-wide effects in an area where water demand often exceeds supply. In addition to the 40 million people who depend on the Colorado River for recreation, agriculture, municipal, spiritual and hydroelectric purposes, declining baseflow has major impacts on riparian, aquatic and terrestrial ecosystems.
âThis region experiences exceptional drought conditions and record reservoir levels at Lake Mead and Lake Powell,â said Katharine Dahm, USGS Rocky Mountain Region Senior Scientist. “The information from this study can be used by resource managers to understand the impacts of water scarcity and develop mitigation plans for people and ecosystems.”
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