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Flagstaff water managers present resiliency scenarios as wildfire and aridification raise supply uncertainty
Summary
City water staff and consultants told the Water Commission that under multiple drought-and-wildfire scenarios Flagstaff will need a new long‑term supply in coming decades, with recommended planning volumes ranging roughly 6,500–12,000 acre‑feet and near‑term contingency supplies of about 4,800–5,000 acre‑feet in catastrophic scenarios.
Flagstaff Water Resources Manager Erin Young and consultant Brad Hill told the Flagstaff Water Commission the city must plan for a range of futures — including hotter, drier conditions and wildfire impacts — and that those scenarios change the timing and scale of when new supplies will be needed.
In opening the presentation, Young summarized the city’s current portfolio: “We pull water from the inner basin of the San Francisco Peaks,” she said, and the utility also relies on Upper Lake Mary, several groundwater wellfields (Woody Mountain, Lake Mary and inner‑city wells) and reclaimed water. Young said reclaimed water and conservation shift the need for new supplies but do not eliminate it.
The presentation centered on scenario modeling Brad Hill prepared to test “resiliency and redundancy” — variations that include slower recharge to Upper Lake Mary, reductions in Lake Mary well‑field pumping, and the loss or temporary shutdown of wells after a severe wildfire. Hill told commissioners, “never to pick a single future because you’ll be wrong,” and said scenario planning is intended to “bracket the timing and when a new supply is needed.”
Why it matters: the city’s 2013 designation of an adequate 100‑year water supply ties some future water availability to infrastructure (for example, securing Red Gap Ranch water requires building a pipeline). Under baseline assumptions in the consultant’s graphs a new supply is required mid‑century; under hotter/drier and wildfire scenarios the need moves decades earlier. Hill gave planning ranges rather than a single number: a commonly modeled near‑term planning point is about 6,500 acre‑feet, while worst‑case combined scenarios pointed toward needs up to roughly 12,000 acre‑feet. In a shock scenario that includes loss of Lake Mary contributions and several Woody Mountain wells, Hill said the city would likely need roughly 4,800–5,000 acre‑feet of short‑term supply and about 9,800 acre‑feet for long‑term replacement in his chosen example.
Supporting details: Young and Hill explained components of the water system and several constraints: - Inter‑basin spring and inner‑basin supplies are highly variable and can provide only a summer‑season supplement (Young: inter‑basin can make up “about 20% of our water supply in the summer months”). - Groundwater is available from Woody Mountain and Lake Mary well fields; Hill and Young said the Lake Mary well field has shown fluctuating groundwater levels and the city has curtailed pumping at times to allow recovery. - The city owns Red Gap Ranch (acquired after a 2005 bond) and past modeling has used a figure of about 16,500 acre‑feet as a potential sustainable development volume; Young said that number is a modeling value and that previous agreements or planning figures cited in public conversation (for example a referenced ~8,000 acre‑feet figure tied to discussions with the Navajo Nation) were not adjudicated water‑rights settlements and should not be treated as settled legal entitlements. - Reclaimed water currently yields roughly 2,000 acre‑feet delivered annually and about 4,000 acre‑feet discharged annually that could be redirected for reuse or recharge in some circumstances; advanced water purification (ADEQ rulemaking) is an emerging option that would allow direct or indirect potable reuse under state rules. - Conservation matters: staff modeling showed lowering total use from a historical ~95 gallons per capita per day toward a 80 GPCD target pushes the timing for a new supply decades later (example presented: a supply trigger moving from about 2035 to about 2048 in one scenario), but conservation alone does not eliminate the need for a new supply at build‑out.
Questions and follow‑ups: commissioners pressed staff on legal and operational constraints for Red Gap (Young: “If we trigger Red Gap Ranch, it's not continuously available under our designation till we build the pipeline”), on wildfire hardening of infrastructure (burying power lines and protecting well‑head sites), and on recharge studies for watershed and stormwater projects. Young said staff has pursued grants (WIFA mentioned) and academic partnerships (NAU researchers) to study recharge rates and that the city has submitted a request to the Bureau of Reclamation for an appraisal‑level study scoped to Flagstaff’s needs and potential regional partners; consultant Kevin Black (former BOR staff) said the Bureau has signaled intent to respond and that the bureau’s appraisal process will be scoped with stakeholders.
Ending: Hill and Young framed their deliverable as analysis for decision makers, not a staff recommendation of a single supply. Hill said the city should begin near‑term actions that preserve options and allow flexibility: “you want to make these decisions in the near term so they'll fit any plausible future,” he said. Staff listed next steps including continued updates to modeling inputs, pursuing the Bureau of Reclamation appraisal investigation, advancing recharge and conservation work, and evaluating capital projects that harden critical well‑field infrastructure.
