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Upper Colorado River Basin loses groundwater faster than drier Lower Basin

Upper Colorado River Basin loses groundwater faster than drier Lower Basin

Built World

Satellite data shows 4.6 trillion gallons lost during 2020-2022 drought — enough to half-fill Lake Powell

October 2026: Study published in Water Resources Research

Overview

Updated 38 minutes ago

The Upper Colorado River Basin lost 4.6 trillion gallons of groundwater during the 2020-2022 drought — enough to half-fill Lake Powell. That's nearly double the loss in the drier Lower Basin, a reversal of what researchers expected from the snow-fed Upper Basin.

A Virginia Tech team combined NASA satellite measurements with surface water, soil moisture, and snow data to track water storage from 2004 to 2023. The findings, published in Water Resources Research, show groundwater losses have accelerated since 2019. The basin's underground reserves, a buffer for 40 million people, are shrinking faster than its reservoirs.

Why it matters

Groundwater is the Colorado River's hidden buffer — if it keeps draining, 40 million people lose a backup supply that rivers and reservoirs can't replace.

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Key Indicators

4.6 trillion gallons
Upper Basin groundwater loss (2020-2022)
Enough to half-fill Lake Powell, nearly double the Lower Basin's loss.
2.5 trillion gallons
Lower Basin groundwater loss (2020-2022)
The drier Lower Basin lost less than the Upper Basin during the same period.
65%
Groundwater share of basin water loss since 2002
Groundwater accounts for most of the Colorado River Basin's total water storage decline.
40 million
People who depend on Colorado River water
The basin supplies farms, cities, and ecosystems across seven US states and Mexico.

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People Involved

Organizations Involved

Timeline

March 2002 October 2026

4 events Latest: October 2026
Tap a bar to jump to that date
  1. Study published in Water Resources Research

    Latest Publication

    Virginia Tech team reports Upper Basin lost 4.6 trillion gallons of groundwater from 2020 to 2022.

  2. Severe drought begins

    Climate

    Triple-dip La Niña reduces winter precipitation across the Southwest, deepening the drought.

  3. Groundwater losses begin accelerating

    Research

    Satellite data shows basin-wide groundwater depletion speeding up after 2019.

  4. GRACE satellite launches

    Launch

    NASA's GRACE satellite begins measuring Earth's water storage from orbit.

Scenarios

1

Colorado River managers fold groundwater into drought plans

Possible Resolves by End of 2028

Discussed by: Virginia Tech researchers and water policy analysts

The study's finding that groundwater and surface water are tightly coupled in the Upper Basin pushes federal and state water managers to treat underground reserves as part of the river's budget. The Bureau of Reclamation or basin states would formally incorporate groundwater measurements into shortage determinations.

2

Groundwater depletion accelerates despite easing drought

Likely Resolves by Oct 1, 2028

Discussed by: NASA researchers and hydrologists

Even if the drought eases, continued agricultural pumping and rising temperatures keep draining aquifers. A follow-up GRACE-based assessment shows basin-wide groundwater storage continuing to decline after 2023.

3

Upper Basin states enact groundwater limits

Possible Resolves by End of 2028

Discussed by: State water agencies and Colorado River negotiators

The finding that the Upper Basin lost more groundwater than the Lower Basin pressures Colorado, Utah, Wyoming, and New Mexico to tighten groundwater regulation, which has historically been weaker than in the Lower Basin. At least one state enacts new statutory limits on extraction.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

September 2014

California's Sustainable Groundwater Management Act (2014)

After a severe drought from 2012 to 2016 exposed unchecked groundwater pumping, California passed the Sustainable Groundwater Management Act. The law required local agencies to form groundwater sustainability agencies and draft plans to bring aquifers into balance by 2040.

Then

The law was the first in California history to regulate groundwater extraction.

Now

It became a model for other western states facing similar depletion.

Why this matters now

Shows how drought-driven groundwater loss can force states to regulate underground supplies — a path Upper Basin states may now face.

1940s-present

Ogallala Aquifer depletion (1940s-present)

Irrigation pumping across the High Plains has drawn down the Ogallala Aquifer for eight decades. In parts of Kansas and Texas, water levels have dropped by more than 100 feet.

Then

Farmers in the hardest-hit areas have shifted to dryland farming or sold land.

Now

The aquifer's depletion has become a permanent constraint on agriculture in the region.

Why this matters now

Shows what happens when groundwater is treated as an unlimited buffer — depletion compounds over decades and becomes hard to reverse.

Sources

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