What will it take to stabilize the #ColoradoRiver? A continuation of the current 23-year-long #drought will require difficult decisions to prevent further decline — Science Magazine #COriver #aridification

Colorado River “Beginnings”. Photo: Brent Gardner-Smith/Aspen Journalism

Click the link to read the article on the Science Magazine website (KEVIN G. WHEELER , BRAD UDALLJIAN WANGERIC KUHN[…], AND JOHN C. SCHMIDT). Here’s an excerpt:

Municipalities of Los Angeles, San Diego, Phoenix, Tucson, Las Vegas, Denver, Salt Lake City, Albuquerque, and Tijuana rely heavily on the river for their water supplies. About 70% of the water is used to irrigate nearly 5.7 million acres (2.3 million hectares) of agriculture. The basin is home to 30 recognized Native American Tribes that hold senior legal rights to divert substantially more water than they currently use. Between 2000 and 2021, the average annual energy generation from the two major dams was 7.6 terawatt-hours (TWh)/year, enough to serve 2.5 million people. The river’s landscapes and ecosystems provide critical habitat for federally protected species and support an extensive recreation-based economy. Today, the entire flow is diverted along its 1400-mile course. In its lower reaches, only 10% of the natural flow reaches Mexico; rarely does the river flow to the Gulf of California…

Current reservoir storage levels could, however, be stabilized if consumptive uses decrease under different scenarios (see fig. S1). If the Upper Basin commits to limit water uses to 4.5 MAF/year (60% of their 7.5 MAF/year allocation, approximately 0.8 MAF/year higher than recent use), then the Lower Basin and Mexico must commit to more than doubling their current maximum reductions in existing use to 3.0 MAF/year (see the figure and fig. S1). In this scenario, the Lower Basin and Mexico receive 66.7% of their allocation, nearly matching the Upper Basin percentage. If the Upper Basin limits their depletions to 4.0 MAF/year (53.3% of their allocation, 0.3 MAF/year higher than recent use), then the Lower Basin and Mexico would need to decrease uses by approximately 2.0 MAF/year to stabilize the reservoirs (see the figure and fig. S1), assuring 77.8% of their allocation. This is close to recently proposed maximum Lower Basin and Mexico commitments to reduce existing use, which would not be invoked until Lake Mead declines further by 3 MAF. Delaying these reductions until then would result in greater loss of storage and stabilization occurring at lower levels than shown in the figure…

Our results show that although current policies are inadequate to stabilize the Colorado River if the Millennium Drought continues, various consumptive use strategies can stabilize the system. However, these measures must be applied swiftly. Although these concessions by both basins may seem unthinkable at present, they will be necessary if recent conditions persist.

Average combined storage assuming drought conditions continue Average end-of-year combined Lake Powell and Lake Mead storage is shown, assuming hydrologic conditions of the Millennium Drought continue. Results show combined reservoir contents using a range of Upper Basin consumptive use limits (colored ribbons) along with a range of Lower Basin maximum consumptive use reductions (line styles) triggered when the combined storage falls below 15 million acre-feet (MAF). The status quo lines use the 2016 Upper Colorado River Commission (UCRC) projections and existing elevation-based shortage triggers. All water use and shortage values are annual volumes (MAF/year).

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