This storage provides a large drought buffer when full. The overall Colorado River reservoir system stores 4 times the annual flow of the river, one of the largest ratios in the world. Despite these smaller recent reductions, Lake Mead continues to decline and in May 2016 it hit a level not seen since its initial filling in the 1930s. This drought has continued into 20 with higher, but still below normal, flows estimated at 94% in 2015 and 94% in 2016 with unusual late season May and June precipitation in both years that raised runoff by nearly 20%.
#OUR GLOBAL FUTURE TEXTBOOK WHEN THE RIVER RUNS DRY FULL#
The Central Arizona Project canal in red.īetween the start of the drought in 2000 and the end of 2014, our analysis period, annual flow reductions averaged 19.3% below the 1906–1999 normal period, and Lakes Mead and Powell, the nation's two largest reservoirs, ended the period at approximately 40% of maximum volume despite starting the period nearly full (Figure 2a). cities receiving Colorado River water, major tributaries, and Lakes Mead and Powell are shown. Record setting temperatures are an important and underappreciated component of the flow reductions now being observed. Fifteen years into the twenty-first century, the emerging reality is that climate change is already depleting Colorado River water supplies at the upper end of the range suggested by previously published projections. Government assessment implies little or no change is likely because precipitation increases will be sufficient to maintain temperature-depleted flows. Nearly all of these studies have cautioned that future warming will deplete the flow of the river, but the results have varied from minor to major. Key PointsĪ large number of studies over the last 25 years have considered the future runoff of the Colorado River (Figure 1) under climate change. These results, combined with the increasing likelihood of prolonged drought in the river basin, suggest that future climate change impacts on the Colorado River flows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur. Precipitation increases may moderate these declines somewhat, but to date no such increases are evident and there is no model agreement on future precipitation changes. Recently published estimates of Colorado River flow sensitivity to temperature combined with a large number of recent climate model-based temperature projections indicate that continued business-as-usual warming will drive temperature-induced declines in river flow, conservatively −20% by midcentury and −35% by end-century, with support for losses exceeding −30% at midcentury and −55% at end-century. Moreover, there is a significant risk of decadal and multidecadal drought in the coming century, indicating that any increase in mean precipitation will likely be offset during periods of prolonged drought.
Whereas it is virtually certain that warming will continue with additional emissions of greenhouse gases to the atmosphere, there has been no observed trend toward greater precipitation in the Colorado Basin, nor are climate models in agreement that there should be a trend.
At least one-sixth to one-half (average at one-third) of this loss is due to unprecedented temperatures (0.9☌ above the 1906–1999 average), confirming model-based analysis that continued warming will likely further reduce flows. Between 20, annual Colorado River flows averaged 19% below the 1906–1999 average, the worst 15-year drought on record.
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