The Colorado River Basin’s groundwater is disappearing faster than the river itself

The Colorado River Basin lost an alarming amount of groundwater over the past 20 years, a new study found. Nearly 28 million acre-feet of water has been depleted from the region, nearly the volume of a full Lake Mead, the country’s largest reservoir.

It’s twice the amount that was lost from the river’s reserves in the same period and the loss is accelerating, the report said. There was a three-fold increase in the rate of depletion over the past decade when compared to the rate of the previous 14 studied.

While significant attention and legislation has been directed to the Colorado River, the water below the surface has not been as heavily scrutinized. To do so, the research team used NASA satellite technology — involving lasers and assessments of gravitational pull on targeted locations — to assess these less visible groundwater supplies. What they found gave them cause for concern.

“We have to be worried,” Karem Abdelmohsen, the lead author of the study and a research scholar at Arizona State University, said. “This is really scary.”

That’s because the Colorado River basin is already struggling with water scarcity. Covering seven states, as well as parts of Mexico, it supplies water to about 40 million people and supports billions of dollars in agriculture.

That scale of demand exists despite what the study, published this week in the journal Geophysical Research Letters, refers to as “unprecedented water management challenges due to the impacts of climate change, including severe aridification and increasing variability in the water cycle.”

In other words, there is an increasing volume and ferocity of droughts across the Southwest, where populations are growing faster than many other parts of the country. The severity of the region’s water woes are well-documented — Arizona, for example, has been in a drought since 1994.

Then there is the declining flow of the Colorado River itself, which has seen a 20% decrease over the past 100 years, with the expectation that by mid-century it might go down another 30%. As access to this “surface water” diminishes, it places a significant pressure on the region’s groundwater — well water that is pumped from underground aquifers — that is the only backstop against running out of water entirely.

In an interview, Abdelmohsen described the situation in personal economics terms. He said surface water supplies like the Colorado River are like a checking account while groundwater is similar to a savings account. Things are good when you are drawing on your checking account per your needs, while also making consistent deposits into your savings.

“Imagine if you start using both accounts at the same time and your savings account is running out of money and whatever is left is not enough for five years, 10 years,” Abdelmohsen said. “If you don’t save water for the future or for the next generation, it will be the same situation.

“The water table will get lower, and as this gets lower, most of the wells will dry up,” he said. “Especially in some areas that don’t have access to surface water, they will not have any water for their farms.”

Should the groundwater continue to deplete at this rate, Abdelmohsen said the region would become fully reliant on the ebb and flow of precipitation and surface water, which would create a situation where the supply would not be able to meet the demand.

Who is most affected?

The states in the Colorado River Basin are split between the upper basin — Wyoming, Colorado, New Mexico and Utah — and the lower basin of Nevada, California and Arizona. It’s the lower basin states that are at the greatest risk should the depletions continue at the current rate.

“Groundwater is a crucial buffer as water supply in arid environments like the (lower Colorado River Basin), but it is rapidly disappearing due to excessive extraction on one hand and insufficient recharge and management on the other,” the report says.

The groundwater in the lower basin makes up 40% of its total water supply and, of all the water depleted in that region during the period of the study, 71% came from those reserves. In the upper basin states, 53% of its regions depletions came from groundwater.

In the discussion section of the report, what the lower basin is facing was summarized: “This scenario places the region’s overall economy and agricultural productivity at significant risk, as an increase in reliance on groundwater is inevitable.”

What can be done?

While the report did not offer a specific plan of action, the authors believe their findings should make Colorado River Basin groundwater issues “a national imperative,” as there are ways to address the problem.

Abdelmohsen pointed out that while surface water is regulated, groundwater is much less so. California has strong regulations in place, as does Utah, but only 18% of Arizona, a state particularly exposed to diminishing water reserves, has any groundwater regulations at all.

First and foremost, Abdelmohsen believes, states and municipalities should find ways to reduce drawing on groundwater so they can begin to replenish these underground aquifers. As agriculture represents 80% of water use, changing from high-water drawing crops, such as alfalfa fed to cattle, is one idea he mentioned. The report also mentions fewer perennial tree crops, and moving from flood-irrigation systems to more efficient systems.

For now, there is no telling how long the groundwater will last as its total supply remains unknown. Abdelmohsen was reluctant to guess since nobody can accurately estimate how much water is held underground.

“This highlights how urgent it is to protect groundwater before the situation gets worse,” Abdelmohsen said. “I see these research findings like an early alarm actually for this water scarcity.”