Fourth National Climate Assessment Volume II #snowpack trends #ColoradoRiver #COriver #aridification

Figure 25.1: Temperatures increased across almost all of the Southwest region from 1901 to 2016, with the greatest increases in southern California and western Colorado.23 This map shows the difference between 1986–2016 average temperature and 1901–1960 average temperature.23 Source: adapted from Vose et al. 2017.23. Map credit: The National Climate Assessment 2018

From The Nevada Independent (Daniel Rothberg):

Aridity is the defining characteristic of the American West, and scientists reported Friday that the region is becoming even more arid due to human-caused climate change, putting states like Nevada at greater risk of water shortages, extreme wildfire, habitat loss and heat waves.

The National Climate Assessment, a 1,656-page report prepared by 13 federal agencies on Friday, painted a stark future in which prolonged droughts could create water insecurity in basins across the Southwest should policymakers not act to mitigate future climate change and adapt to changes already underway. In addition to causing disruption to everyday life, climate change in the Southwest is expected to affect industries like agriculture and ranching.

Nevada, the most mountainous state in the contiguous U.S. and the seventh largest state by area, straddles several ecosystems that would likely be harmed by hotter temperatures and changes to precipitation. Many of these early effects are already apparent, the report noted.

In the past two years alone, northeastern Nevada saw the state’s largest single fire while Southern Nevada saw an increase in heat-related deaths amid record-breaking summer temperatures.

“These are alarm bells that are going off right now,” said David Breshears, a University of Arizona ecologist and a report co-author, pointing to extreme wildfires and water shortages across the region.

The report cited dropping water levels at Lake Mead, the reservoir created by the Hoover Dam about 30 miles from Las Vegas, as a prime example of how climate change has affected regional water supplies. Lake Mead, the largest reservoir on the Colorado River system, stores water for millions of Americans and hundreds of farms downstream in Southern Nevada, California and Arizona.

Since the nearly two-decade drought began in 2000, the snowpack-fed reservoir has lost about 60 percent of its water because of overuse and arid conditions worsened by climate change. A paper released earlier this year showed that Colorado River streamflow has decreased by about 15 percent over the past 100 years with half of those decreases attributed to higher temperatures.

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