While the seven Colorado River Basin states including Arizona hunt for 500,000 acre-feet a year in water savings in both the Upper and Lower basins, the biggest problem facing the river lurks in the shadows: a supply-demand gap that keeps growing.
Over the past five years, the riverβs annual water flow, greatly diminished since 2000 compared to 20th century averages, has tumbled even faster. Water demands have also fallen, but not nearly as fast.
The result is an annual deficit far greater than the 500,000 acre-feet of additional water that savings that Upper and Lower basins state water officials hope to achieve annually in their respective basins over the next few years through short-term conservation plans, to prop up Lakes Mead and Powell. The deficit is also most likely more than the 1.1 million acre-feet a year of river water that the Lower Basin states of Arizona, California and Nevada have already agreed to save over the entire course of their drought contingency plan, which they approved in 2019.
Officials say they hope to find ways to close that gap as part of renegotiations of state and federal guidelines for operating the reservoirs that expire at the end of 2026.
βIf youβre asking me if 500,000 acre-feet of savings will prevent Lake Powell from hitting 3,490 feet, I donβt think so,β said Colorado Water Conservation Board chair Jaclyn Brown, referring to the elevation at which the adjoining Glen Canyon Dam would no longer be able to generate electricity.
Sometime this summer, the U.S. Bureau of Reclamation is scheduled to take the first step toward renegotiating the guidelines, when it posts a Federal Register notice seeking comments from cities, farms, tribes and other entities and individuals on precisely what subjects the new guidelines should cover. But as has been discussed at numerous conferences, interviews and research papers over the years, major differences exist among the various parties involved in water as to what areas should be covered in the guidelines, let alone their substance.
Annual deficits
Here are three ways of looking at the riverβs deficit:
Since 2000, the Coloradoβs average annual flow at Leeβs Ferry, the boundary between the two basins lying just west of the dam, has declined to about 12.2 million acre-feet compared to about 15 million from 1906 to 2000. But the flow has averaged about 10.6 million acre-feet annually over the past five years, including an expected 10.3 million acre-feet in 2022. Leeβs Ferry is where the Bureau of Reclamation measures annual natural river flows.
As of 2020, the most recent year for which statistics are available, annual water use in both basins and Mexico was about 14.3 million acre-feet, matching the average annual use in almost every year since 2010. That figure includes evaporation in reservoirs. That puts the river at a deficit of about 2.1 million acre-feet, using the 12.2 million figure annual average supply figure as a baseline.
But looking at only the average annual supply over the past five years raises the deficit to at least 3 million-acre feet a year.
The deficit shrinks some, however, when you also account for additional water that flows into the river downstream of Leeβs Ferry from tributaries such as the Little Colorado and Paria rivers. Jack Schmidt, a Utah State University professor and water researcher, estimates an annual average of 760,000 acre-feet entered the river from tributaries and springs near the Grand Canyon from 1990 to 2021. The average has dropped to 710,000 acre-feet a year since 2017. The reclamation agency estimates about 780,000 acre-feet of additional tributary and spring flows.
Adding that water and looking over a 22-year period, the deficit would average about a million acre-feet a year. Looking at only the past five years, including 2022, it would be in the 2.5 million acre-foot a year range.
Thatβs not far from the 3.2 million acre-foot deficit that Reclamation had predicted in a 2012 study could exist by around 2050.
Looking instead at total water storage in Lakes Powell and Mead, they held 43.4 million acre-feet on Sept. 30, 2000. By Sept. 30, 2021, their total storage had tumbled, on average, 1.2 million acre-feet a year to 16.3 million acre-feet.
That annual loss is a few hundred thousand acre-feet less than all the water that Tucson, Phoenix and other Arizona cities, farmers and tribes got every year from the 336-mile-long Central Arizona Project canal system until CAP suffered its first mandatory cutbacks of about 512,000 acre-feet in 2022, as required by the Lower Basin drought contingency plan.
Schmidt, director of Utah State Universityβs Center for Colorado River studies, noted the scientifically accepted strategy for measuring and predicting annual river flows has been to rely on 30-year averages. But the sharp decline in flows since the turn of the century raises questions about that, and a recent paper by the center makes that point in critiquing past federal predictions of water levels at Mead, Powell and other reservoirs.
The Bureau of Reclamation uses 30-year averages of temperature and precipitation to help it make monthly forecasts for reservoir elevations looking 24 months ahead. It recently updated forecasting methods, to base predictions on the period 1991 through 2020 instead of 1981 through 2010. But while that switch will likely improve forecasting, projections βare likely to remain biasedβ in favor of wetter forecasts because the 1991-2020 period was wetter than the millennium drought period from 2000 to the present, the centerβs February 2022 paper concluded.
The last five years worth of deficits on the river are actually less than those that struck during another severe dry cycle on the Colorado from 2000 to 2004. In those five years, the river got about 9.5 million acre-feet of natural flow annually at Leeβs Ferry, compared to 10.5 million acre-feet from 2018 through 2022.
But while river flows rose and stabilized some from 2005 through 2012, that wetter period didnβt produce enough runoff for reservoir levels to recover to pre-2000 levels when they were nearly full, said Schmidt.
βAll that we got was a pause in the emptying. Then when the flows got low again in 2012 and 2013, the reservoirs took another hit. From 2012 through 2018, we started catching our breath again, but boom. Look at 2020, 2021 and 2022, and theyβre going to be down there again,β Schmidt said.
βWeβre sort of going in stairsteps,β with flows dropping then rising but not bringing reservoirs back to where we were, then dropping again, Schmidt said. Now, theyβre at their lowest levels on record: 31% of capacity at Mead and 24% at Powell.
Account overdrawn
Overall, βweβve been overdrawn. I would liken it to a checking account and a savings account. If Lake Mead is the checking account, and the Lower Basin is overdrawing that account, then water is pulled from Powell, which is our savings account,β said Jim Lochhead, CEO and manager of the Denver Water utility, in a recent virtual presentation done for the University of Arizonaβs Water Resources Research Center. Lochhead said. βAnd weβre in a situation today where the checking account is overdrawn and the savings account is depleted.β
Fixing the deficit βis going to require very hard and difficult conversations among the basin states. it will require significant reductions in water use, well beyond what has been felt so far,β Lochhead said. βWe need to build up that bank account again. The system has been operated on the hope that the hydrology will bail us out. It hasnβt happened.β
In the Las Vegas area, Southern Nevada Water Authority Deputy General Manager Colby Pellegrino said the authority is implementing new conservation programs at almost every board meeting.
βWeβve got to continue to try to drive our demand down,β said Pellegrino.
When the seven basin states and the federal government start renegotiating the 2007 reservoir guidelines that expire in 2026, βthatβs where I think we are really going to get to the meat of the discussion of how much we need to conserve,β Pellegrino said. βI donβt think the (Upper and Lower) basins will be resilient in the face of a changing climate without taking a much more serious look at our water demands.β
Historic imbalance
Why has this deficit kept growing?
The decline in Lake Powell is directly related to low inflows in the Colorado River system since 2000 along with water depletions across the basin in excess of supplies, replied Chuck Cullom, director of the Upper Colorado River Commission, an administrative interstate water agency managing Colorado River issues for the Upper Basin.
This historic imbalance between depletions, which includes evaporation as well as human water use, and available flows has historically been countered by pulling water thatβs stored in the reservoirs, he said. But those continued pressures are whatβs triggering the declines in water levels.
Speaking specifically of Powell, Cullom said its decline is primarily βdue to difference between releases from Lake Powell to meet downstream depletions and the low inflows to Lake Powell due to prolonged drought and climate change.β
Using less diplomatic terms, many other Upper Basin water officials pin the majority of the blame on the Lower Basin states of Arizona, Nevada and California. Thatβs because the Lower Basin uses much more water each year than the Upper Basin, and more than what flows downriver from Powell. Upper Basin states are New Mexico, Utah, Colorado and Wyoming.
Various estimates put Upper Basin depletions, including evaporation and water sucked down by riparian trees and shrubs, at 4.4 million to 5.1 million acre-feet annually. In the Lower Basin, the federal government estimated in 2015 the three statesβ and Mexicoβs users removed 10.5 million acre-feet, including evaporation and other, unspecified βsystem losses.β For 2022, that estimate dropped to 9.9 million, due to water delivery cuts required by the 2019 drought plan.
Some Lower Basin water users, however, note the Upper Basin states so far have done little or nothing collectively to conserve river water since they approved their drought plan in 2019. The Lower Basin, by contrast, instituted the first in a series of water use cuts this year due to the drought plan. It also has approved a shorter-term, β500-plusβ plan to cut another 500,000 acre-feet in 2022 and 2023 by paying willing users to temporarily give up supplies.
βWhen we get into renegotiating the (2007 reservoir) guidelines with those characters we will have rough sledding. Theyβre beginning to believe their own P.R. Those guys are putting their heels in the ground up there,β said Bart Fisher, a longtime farmer and vice president of the Palo Verde Irrigation District that operates near Blythe, California, at the Arizona border. Last year, it agreed to sell up to 20% of its river water supplies for three years for $38 million to various state, municipal and federal water agencies, to have the water kept in Lake Mead.
βWeβre helping ourselves; the Upper Basin is not doing that. Theyβre digging in, bickering between themselves,β Fisher said, adding he was speaking for himself and not as an official of the irrigation district.
But individual Upper Basin users have voluntarily taken water shortages from the river 20 of the past 21 years, countered Steve Wolff, director of the Durango-based Southwest Water Conservation District. The difference is in the Upper Basin, whose farms and cities mostly lie upstream of Lake Powell, depends on year-to-year swings in water availability from snowpack and runoff, said Wolff. The shortages there are often taken piece by piece among individual users rather than by big water districts as is done in the Lower Basin.
βWe donβt have the big storage units to feed our needs,β he said, since the big reservoirs lie downstream of where most Upper Basin water users live and work.
But thereβs little benefit in pointing fingers regarding the deficit because that doesnβt help solve it, said water researchers John Fleck at the University of New Mexico, Sarah Porter at Arizona State University, and Southern Nevada water official Pellegrino. Rather than talking about blame βwe should talk about how we deal with the imbalance,β said Sharon Megdal, director of the UAβs Water Resources Research Center.
