Overuse of Groundwater in CRB Threatens Sustainability

 

Declining Freshwater Availability in the Colorado River Basin Threatens Sustainability of Its Critical Groundwater Supplies Karem Abdelmohsen, James S. Famiglietti, Yufei Zoe Ao, Behshad Mohajer, Hrishikesh A. Chandanpurkar; First published: 27 May 2025  https://doi.org/10.1029/2025GL115593

The article below is excerpted from the research cited above and the LinkedIn post of James S. Famiglietti.

From Famiglietti et al

Climate change is causing more frequent and intense droughts around the world, including in the Colorado River Basin, which supplies water to seven U.S. states and Mexico, and is facing severe water shortages. The researchers used data from the NASA GRACE and GRACE Follow-On (GRACE-FO) satellite missions, land surface models, and in situ data over the past two decades to examine and document the groundwater depletion in the Colorado River Basin.

As Colorado River streamflow diminishes, the reliability of surface water resources has become increasingly threatened. Over the past century, the river's flow has decreased by approximately 20%, and climate models predict further reductions of up to 30% by the mid-21^st century due to rising temperatures and reduced snowpack in the Rocky Mountains, which feed the river.

Although all seven states have equal priority under the 1922 Colorado River Compact, under the 2007 Interim Guidelines, Arizona faces the largest mandatory reductions in water deliveries when Lake Mead reaches critically low elevations (Bureau of Reclamation, 2020). Arizona represents a substantial portion of the Lower Colorado Basin in terms of land area and water use, and faces potentially losing up to 512 million cubic meters (approximately 415,000 acre-feet) of its annual allotment if water levels in Lake Mead continue to decline (Bureau of Reclamation, 2020). 

The decline of the river poses a severe threat to both agricultural and municipal water supplies, which are heavily reliant on the river. Approximately 80% of the Colorado River Basin's water is used for irrigation (which supports a $1.4 billion agricultural industry in Arizona alone.

from Famiglietti et al (both charts)

declining groundwater storage in Upper and Lower Colorado River Basin

The declining river flows and reduced allotments places immense pressure on the region's groundwater resources which have been used to make up the difference. As surface water becomes less dependable, the demand for groundwater is projected to rise significantly. In the Lower Colorado River Basin, groundwater already accounts for approximately 40% of the total water supply and is expected to increase. However, the lack of robust protection and management strategies for groundwater in the Colorado River Basin puts these resources at significant risk of over-exploitation. Groundwater is a crucial buffer as water supply, but it is rapidly disappearing due to excessive extraction on one hand and insufficient recharge and management on the other. 

This research highlights the importance of understanding the factors affecting groundwater levels to create sustainable water management strategies that can help secure water resources for the region's future. The research found that:

• The Colorado River basin has lost 27.8 MAF of groundwater since 2003. This is roughly the equivalent of the volume of Lake Mead, and it represents two-thirds of the losses of total water storage.
• Groundwater losses in the Colorado River basin were 2.4 times greater than the losses of surface water in Lakes Powell, Mead, and other smaller reservoirs (11.67 MAF), yet groundwater receives scant little policy and management attention relative to the reservoir levels and the flows of the Colorado River.  
• Most of the losses occurred in the dryer, Lower Colorado river basin, which lost 20.7 MAF of groundwater since 2003, and accounts for 71% of the total water loss (29.2 MAF) in the lower basin.
• Total water storage losses in the Colorado River basin have accelerated by a factor of 3 in the last 10 years compared to the previous decade.

The work suggests that, in states like Arizona, where only 18% of the area of the state has groundwater management, that expansion of groundwater management across the entire state is a critical step towards preserving this precious resource for future generations and for the long-term economic vitality in the region.