Struggling for Sustainability on the Colorado River

The 900-year old Nankoweap Granaries perched high above the Colorado River provide an inspiring setting for contemplating the future of a river that has provided sustenance and well-being for so many, for so long. These granaries were built by Ancestral Puebloans. Photo by Brian Richter

______________

My personal connections to the Colorado River run long and deep.

I grew up in San Diego during a time when virtually all of that city’s water supply came from the Colorado River. Given that two-thirds of the human body mass is comprised of water, I carried some 15 gallons of Colorado River water around in those days, connecting me physically to the river.

Subsequently, during three decades of work with The Nature Conservancy, the plight of ancient but now highly endangered species was always at the center of our deliberations about restoring the river. When you contemplate the fact that some of these species like the Colorado pikeminnow have been navigating the river’s currents since the Grand Canyon began to form, you can’t help but feel a natural heritage connection — and a moral obligation — to do whatever you can to ensure their persistence.

All of which is to say that I care a great deal about the fate and future of the Colorado River.

In previous blogs I’ve offered my opinions about what needs to be done to sustain the river into the future. In this blog I’ll provide an update on the river’s current status.

The River in 2020

There was a good bit of media optimism at the end of last year when it was announced that water use in the Lower Basin had dropped to its lowest level since the turn of the millennium in 2000. Some even heralded that Lake Mead was “back on the rise” after the reservoir level rose eight feet last year. However, these good-news proclamations appear to have been premature.

Last year was the third biggest runoff year since 2000, and when it rains a lot we use less water to irrigate our residential and commercial lawns and golf courses, or to irrigate crops. And when the Colorado River has a lot of water it is often the case that other water sources are running strong as well. All of that tends to lead to less water use from the Colorado.

Because the Sierra Nevada produced a lot of snowmelt runoff into the Sacramento and San Joaquin rivers last year, the Metropolitan Water District (MWD) of Southern California — which serves many large urban areas including Los Angeles and San Diego — didn’t have to rely so heavily on diversions from the Colorado River, and its draw from the Colorado last year was the lowest in decades (see graph below).

In contrast, MWD’s allowance for diverting water from the Sierran rivers is much lower this year, and as a consequence their diversion from the Colorado is much higher. MWD projects that it will use an estimated 829,000 acre-feet from the Colorado this year (see star in graph below), a 50% increase over last year.

Fortunately, water use by the Colorado River’s biggest consumers has been holding flat or dropping in recent decades (see stars in graph above).

Unfortunately, total water use in each of the three Lower Basin states is either flat (Arizona) or will increase this year (California and Nevada). This will cause the total water use in the Lower Basin to be higher this year as well (see graph below).

The Big Reservoirs in 2020

Heavier water use, combined with very meager runoff from the Rockies, is leading to a substantial lowering of Lakes Mead and Powell this year.  The Bureau of Reclamation is projecting that by calendar year’s end, Lake Powell’s level will have dropped by 21.2 feet to elevation 3587.6, or 41% of capacity. Lake Mead will be down by 5.3 feet from last year at elevation 1085.2, or 38% of capacity.

On May 14th of this year, I predicted that Powell would drop by 22 feet, so I was pretty close! I projected that Mead would drop by 9 feet, but I did not account for the benefit of the new Drought Contingency Plan for the Lower Basin. The DCP forced a reduction of 341,000 acre-feet of use, translating into four feet of water in Lake Mead, so the reservoir will end up losing only five feet of water this year.

Looking a little ahead, the Bureau of Reclamation is now forecasting that Powell will drop by another 11.5 feet next year to elevation 3576.1 and end up at 37% of capacity. However, they project that Mead will rise by a foot and a half, largely due to the fact that they expect to release a lot more water (9.0 million acre-feet) from Lake Powell next year (this year’s release was only 8.23 MAF).

A Long Road to Sustainability

These numbers and trends suggest that we’re still a long way from balancing the water budget of the Colorado River; my latest calculations suggest that we’re using 17% more water than the river produces, on average. Unless we start to substantially and quickly reduce our draw from the river, things will almost certainly worsen under a warming climate that will reduce the flow of water in the river. In next week’s blog I’ll share some recent analyses I’ve performed that look at how the river, and the big reservoirs, might be affected by climate change.  Stay tuned!