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The twenty‐first century Colorado River hot drought and implications for the future

States that between 2000 and 2014, annual Colorado River flows averaged 19% below the 1906–1999 average, the worst 15‐year drought on record
At least one‐sixth to one‐half (average at one‐third) of this loss is due to unprecedented temperatures (0.9°C above the 1906–1999 average), confirming model‐based analysis that continued warming will likely further reduce flows
States that, 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
States 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
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
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
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

The twenty‐first century Colorado River hot drought and implications for the future

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