In a chapter dedicated to climate change effects in the Southwest, climate scientists said “with very high confidence” that high temperatures are reducing the water content of mountain snowpack and the flows of rivers and streams that depend on snowmelt.
The chapter’s landing page features a photo of low water levels at the nation’s largest reservoir, Lake Mead outside Las Vegas, a nearly perfect symbol of the region’s ongoing water challenges.
In addition to sapping the nation’s largest desert reservoirs, the report said, the changing climate also is leading to more intense droughts, increasing the risk of severe floods, weakening key infrastructure projects and depleting groundwater.
In a scenario where greenhouse gas emissions increase, the report said, the entire region could see its average annual temperature rise an additional 8.6 degrees by 2100.
Southern parts of the region, which include Phoenix, Tucson and San Diego, could see their summers extend well into the spring and fall, with 45 more days each year where temperatures climb past 90 degrees.
Each drought is the product of particular circumstances, the report noted, and can be intensified by dwindling groundwater, which in some regions acts as a buffer against scarce surface-water supplies.
Shrinking snowpack likely to continue Southern Rocky Mountain snowpack in Colorado, Wyoming and Utah supplies the vast majority of river flows in the Colorado River watershed.
Higher temperatures, especially at lower elevations, result in precipitation falling as rain, which holds less water than snow.
To make up for reduced streamflows, the Southwest would need a large increase in precipitation, something the report doesn’t predict.
The severity of water shortages in the Southwest is largely up to us, as the report noted in its section on how confident climate scientists are in their findings: “The actual frequency and duration of water supply disruptions will depend on the preparation of water resource managers with drought and flood plans, the flexibility of water resource managers to implement or change those plans in response to altered circumstances, the availability of funding to make infrastructure more resilient, and the magnitude and frequency of climate extremes.” This story is part of a project covering the Colorado River, produced by KUNC and supported through a Walton Family Foundation grant.