How low can the #ColoradoRiver go? #Drought forces states to face tough choices about #water — The #Arizona Republic #COriver #aridification

Click the link to read the article on the Arizona Republic website (Brandon Loomis). Here’s an excerpt:

Water managers from across the Colorado River Basin are preparing to negotiate new rules for allocating the river’s dwindling flow and sharing the pain of a deepening shortage. They’re adapting the 100-year-old Colorado River Compact to a river that little resembles the bountiful gusher that negotiators from seven states and the federal government in 1922 thought — or hoped — would bless the Southwest forever. The stakes rise with every foot that Lake Mead and Lake Powell fall, as the states and the water users within them recognize they’re due for a tighter squeeze.

Las Vegas Lake Mead intake schematic, courtesy SNWA.

Arizona gets more than a third of its water from the river, growing abundant crops around Yuma and homes around Phoenix and Tucson. The Las Vegas area gets most of its water from the river and has built a deeper pipe in Lake Mead to assure its continued access. Late-developing states like Wyoming use water for ranching and energy development, and are hoping to continue growing on it…

Re-thinking the river’s flow

Before the states, Indigenous communities and water districts can agree on a new plan to more conservatively divvy the water, they’ll need to agree on how low the river might go…

The 2022 negotiators are debating whether they should plan for just 11 million acre-feet, as Entsminger’s Nevada agency already has penciled into its water security plans…

Brad Udall: Here’s the latest version of my 4-Panel plot thru Water Year (Oct-Sep) of 2021 of the Colorado River big reservoirs, natural flows, precipitation, and temperature. Data (PRISM) goes back or 1906 (or 1935 for reservoirs.) This updates previous work with
@GreatLakesPeck.

Since 2000, the river has delivered on average 12.3 million acre-feet a year, which is generally a couple of million less than the region has used. Consequently, the giant reservoirs that were full back then have tanked, Lake Mead to about a third of capacity, Lake Powell to a quarter…Planning for a regular supply of just 11 million acre-feet would obliterate long-held assumptions about how much water some or all of the users thought they were entitled for future growth. Contingencies for that level could severely limit growth potential in the Upper Basin, where Wyoming, Colorado, New Mexico and Utah are far from fully developing their collective 7.5 million acre-foot share outlined by the compact…

Climate scientists who study and project the Colorado’s flows as the region warms believe even 11 million acre-feet could be wishful thinking. Some studies suggest heat’s toll on the water supply will drop the river to just 9 million acre-feet in coming decades, said Brad Udall, a Colorado State University researcher who has focused on the river for 20 years. “I could live with 11” as a planning guideline, even if it’s optimistic, Udall said. That projection is stark enough to require bold action that water managers could later build upon. It would follow the trajectory that scientists like Udall say represents the region’s heat-induced aridification, as opposed to temporary drought.

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