January 10, 2021
Arizona started 2020 operating for the first time under the Drought Contingency Plan’s (DCP) Tier Zero. This reduced Arizona’s Colorado River supplies by 192,000 acre-feet. By agreement, Central Arizona Project (CAP) took this entire reduction, representing 12% of its normal annual Colorado River water supply. For CAP customers, this eliminated water that would have been available for underground storage, banking and replenishment. Water for CAP agricultural uses was reduced by about 15%.
The Tier Zero reduction to CAP, while significant, was largely equivalent to the amount of Colorado River water CAP had been leaving voluntarily in Lake Mead since 2015 as part of its Lake Mead Conservation Program. In essence, CAP and its water users planned and prepared for Tier Zero reductions for the past five years. Those previous contributions were voluntary – now, under DCP, these contributions are mandatory.
Based on the U.S. Bureau of Reclamation’s (BOR) August 24-Month Study, it appears Arizona will continue in Tier Zero through 2021. With DCP a success, Arizona now will turn its attention to the future. The current 2007 Guidelines, along with the DCP overlay, will expire on Dec. 31, 2025. The U.S. Secretary of the Interior will be developing new guidelines for the long-term management of the Colorado River system. This process will take many years and require multiple levels of discussion, negotiation and coordination within Arizona and the Basin states.
To ensure Arizona remains stronger together, the Arizona Department of Water Resources and CAP have reconvened the Lower Basin Drought Contingency Plan Steering Committee delegates to form the Arizona Reconsultation Committee (ARC). The ARC Committee is tasked with developing an Arizona perspective on the reconsultation of 2007 Guidelines. Its members represent Arizona’s diverse water interests, including elected leaders, tribes, cities, farms, industry and environmental groups.
The challenges all Colorado River water users across the basin face as we enter these negotiations are serious: drought, over-allocation, growing water needs and the prospect of a drier future. Arizona will use the strength of its diverse water users and stakeholders, through the ARC process, to guide and inform an approach to addressing these challenges in the reconsultation negotiations.
At the same time, within Arizona the water year 2020 started with a wet November and December (125% to 200% of normal snowpack), and ended the winter season with the 12th wettest March on record. The end result was a total inflow of 150% of median for the winter runoff season (January through May). Roosevelt Lake increased from 66% to 99% full, nearly reaching capacity in April. On the Verde River system, reservoirs were at capacity by mid-March spilling approximately 30,000 acre-feet of water over Granite Reef Dam during the month.
The 2020 monsoon season ended up being the driest ever recorded over the Salt River Project’s (SRP) 121 year period of record. At just 30% of normal, an overall average of only 1.93 inches of precipitation was recorded across the watersheds. However, because of the wet winter, the reservoir levels are in good shape with total storage at 80% as of Sept. 1, compared to 70% at the same time last year. Total projected inflow for water year 2020 is approximately 1,058,000 acre- feet (116% of median). Climate predictions for the upcoming winter indicate a shift toward a weak La Nina indicating that the upcoming winter has a greater chance of drier conditions.
SRP is sponsoring an Appraisal Study that is being led by the Bureau of Reclamation to evaluate options to mitigate the nearly one-third of storage capacity loss due to natural sedimentation accumulation at Horseshoe Reservoir on the Verde River. The Verde Reservoirs Sediment Mitigation Study has incorporated a diverse group of stakeholders to help find a solution to a problem, that if left unchecked, will continue to diminish SRP and the City of Phoenix carry-over storage capacity in the reservoir. The loss of capacity is reaching a critical mass at a time when the Phoenix Metropolitan Area needs these water supplies more than ever in light of anticipated hydrologic impacts of climate change and potential shortage conditions on the Colorado River. The appraisal study is expected to be complete in 2021 and contribute to an action plan to restore the lost capacity.