Water and Climate Change

Upper Lake Mary Spillway
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Objective 6: Ensure Adequate Water Resources and Plan for Climate Change

Relevant Standards

  • Maintain 100-year Adequate Water Supply Designation as administered by the AZ Department of Water Resources
  • Ensure that the risk of a sustained water delivery shortage is extremely low
  • Continue to build resiliency in water supplies and infrastructure systems with specific attention to the forecasted effects of climate change
  • Maintain a diverse and redundant water-supply portfolio, including optimizing the use of reclaimed water
  • Encourage efficient water use while maintaining quality of life
  • Conduct water loss assessments, per AWWA standard


Flagstaff’s water supply currently comes from three sources, Upper Lake Mary, pumping water from deep aquifers (approximately 1000-2,000 feet below the ground), and reclaimed water. Upper Lake Mary has always been a highly variable supply, its yield determined by yearly snowpack and precipitation. The deep well aquifers have provided a reliable source of high-quality water. Flagstaff residents and businesses have cut water use per-capita by over 50% since 1989.


  • Climate change models indicate accelerating uncertainty about yearly snowpack and precipitation, potentially decreasing the availability of Upper Lake Mary as a water resource and impacting aquifer levels.
  • Loss of Upper Lake Mary would increase costs due to pumping of additional groundwater and trigger the search for a new water resource.
  • Although Flagstaff currently maintains its 100-year Adequate Water Supply Designation, the City pumps more groundwater in certain well fields than is naturally replenished by snowpack and rain.
  • Future natural replenishment could decrease significantly with climate change.
  • Increased temperatures and “longer summers” will increase overall water demand.
  • Water resources planning and engineering codes must consider future conservation efforts, including the effects of “demand hardening” on supply reliability and the impacts on wastewater collection and treatment.

Timing Concerns

Climate change is accelerating, resulting in increased uncertainty in water supply issues, indicating more aggressive planning and communications should begin now.

Specific Responses

  Champion Action Items Timing
1.    Update planning with respect to Flagstaff’s water                       resource and climate change impacts, including updating         the risks associated with current water resources and the         100-year supply designation (Water Resources Master               Plan). _________________ _______________________
2.    Update predictions on the ongoing yield of Upper Lake             Mary based on climate change considerations Increase             monitoring and management of aquifer water levels                   through strategic operations and better understanding of         recharge rates and its locations.      
3.    Continue promoting water-use efficiency, as per the                   adopted 2020 Water Conservation Strategic Plan Increase         the use of reclaimed water, including recharge to                       augment groundwater supplies and evaluating other                 options, such as Direct Potable Reuse.      
4.    Develop measures that establish a sustainable water                 budget, or safe yield of groundwater by 2033 (the 20-year         period established by ADWR in the Adequate Water                  Supply Designation).      
5.    Work to foster a continued community conservation ethic         to ensure future supply reliability (considering the                     impacts of demand hardening on reliability, the                           wastewater treatment system, and reclaimed water).      
6.    Enhance communications on climate change and water             resources, including clearing up confusion related to the           difference between infrastructure and water resource                 limitations.      

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