Declining Freshwater Availability in the Colorado RiverBasin Threatens Sustainability of Its Critical GroundwaterSupplies

Geophysical Research Letters Volume 52, Issue 10 May 2025

By Karem Abdelmohsen, James S. Famiglietti, Yufei Zoe Ao, Behshad Mohajer, and Hrishikesh A. Chandanpurkar

Overview: Groundwater depletion in the Colorado River Basin poses a significant threat to sustainability, underscoring the need for enhanced management practices. ​

Groundwater Depletion in the Colorado River Basin ​

• Groundwater depletion accounts for 65% of total terrestrial water storage (TWS) loss in the Colorado River Basin (CRB). ​
• The Upper Colorado River Basin (UCRB) lost 14.6 ± 3.5 km³ of total water storage (TWS), with 53% attributed to groundwater (7.8 ± 5.3 km³). ​
• The Lower Colorado River Basin (LCRB) lost 36.0 ± 6.2 km³ of TWS, with 71% from groundwater (25.5 ± 7.4 km³). ​
• Annual groundwater extraction rates should align with depletion rates: 0.35 km³/yr in UCRB and 1.15 km³/yr in LCRB. ​

Impact of Climate Change

• The CRB faces persistent aridification due to climate change, leading to increased drought frequency and reduced freshwater availability. ​
• The average temperature in the region has increased by approximately 0.8°C over the past century. ​
• Streamflow in the Colorado River has decreased by about 20% over the last century, with predictions of further reductions up to 30% by mid-century. ​

Groundwater Management Practices ​

• Groundwater management practices and access to surface water have reduced depletion rates in managed areas of LCRB compared to unmanaged regions. ​
• The expansion of groundwater management and inclusion in interstate water discussions may help achieve sustainability. ​
• Only 18% of Arizona’s area is subject to groundwater management, indicating a need for broader strategies. ​

Agricultural Water Use ​

• Agriculture accounts for approximately 80% of CRB’s water use, significantly impacting groundwater resources. ​
• In LCRB, groundwater already provides about 40% of the total water supply, with usage expected to rise as surface water availability declines. ​
• The top 15 water-intensive crops account for 71% of total crops in rapidly depleting basins, emphasizing the need for crop diversification. ​

Recommendations for Sustainability

• Shifting from water-intensive crops to more water-efficient alternatives can help reduce groundwater depletion. ​
• Implementing efficient irrigation methods, such as drip irrigation, is crucial for sustainable water management. ​
• Federal oversight may be necessary to ensure effective groundwater management in conjunction with surface water allocations. ​