What the data says, stated plainly
Purpose
The purpose of this page is to state the principal findings that follow from closing the Great Salt Lake water ledger under consistent definitions, system boundaries, and time periods. It identifies what the reconciled physical record demonstrates about climate, human depletions, lake response, and recovery while keeping accounting results separate from analytical attribution, forecasts, and policy judgments.
These conclusions are not forecasts. They are accounting outcomes derived from a physically closed ledger applied consistently across three defined time periods: the 1961–1990 baseline, the 1996–2025 30-year rolling period, and the 2021–2025 shock period.
Conclusion 1: The 2021–2025 elevation crisis was primarily driven by climate—but long-term human depletions lowered the lake’s starting elevation
This conclusion is supported by the datasets assembled in this framework but differs from the emphasis commonly found in policy discussions and media coverage of the lake’s decline.
Basin-scale inflow—measured at the four Zone 1 terminal gages—Bear River at Corinne, Weber River near Plain City, Jordan River Surplus Canal, and Jordan River at 1700 South—averaged 2,317 kaf/year during the 1964–1990 baseline period and 1,571 kaf/year during the 1996–2025 30-year rolling period. These gages measure water leaving the major tributary systems before it passes through Bear River Bay, Farmington Bay, and associated wetland complexes on its way to the open lake. During the 2021–2025 shock period, basin-scale inflow plummeted to 1,318 kaf/year. The Bear River at Corinne alone—the single largest inflow source—averaged 1,429 kaf/year at baseline, 929 kaf/year in the 30-year rolling period, and 769 kaf/year during the shock. That is a 46 percent decline in the primary inflow gage from the baseline period to the shock period.
Human depletions did not change materially between the 30-year rolling period and the shock period. The 2026 Strike Team depletion table and the reconciled depletions dataset used in this framework confirm this. Human-caused depletions are large and chronic, but they were not the principal driver of the crisis timing.
What changed was climate. KSLC precipitation averaged 16.22 inches per year at baseline, 15.15 inches in the 30-year rolling period, and 13.85 inches during the shock. Mean annual temperature rose from 52.2°F at baseline to 56.5°F during the shock—a 4.3°F increase that drives evapotranspiration and reduces effective basin yield independent of any change in human use. The 2026 Strike Team (Figure 12) confirms that inflow has declined since the late 1980s "even with no notable increase in human water depletions."
The South Arm elevation record confirms the sequence. Annual mean elevation was 4,199.6 ft during the baseline period, 4,195.9 ft during the 30-year rolling period, and 4,191.9 ft during the shock. The 3.7-foot decline from baseline to the 30-year rolling period occurred over decades and reflects the combined effect of growing human depletions and modest early climate shift. The additional 4.0-foot crash from the rolling average to the shock average occurred in four years and cannot be explained by depletion growth. It is a climate-driven basin yield collapse. That said, the lake’s starting elevation at the onset of the shock was already approximately 2 feet below its estimated mid-twentieth century equilibrium due to decades of cumulative human depletion, meaning the shock produced a lower bottom than it would have from a higher baseline.
Any analytical or policy framework that attributes the acute 2021–2025 elevation crisis primarily to human consumption is inconsistent with this data. The chronic human contribution documented in Conclusion 2 is a separate and distinct finding.
Conclusion 2: Human depletions are responsible for a chronic 2-foot depression of the lake’s natural operating range—and that depression compounds every climate shock
While the acute crisis was primarily climate-driven, human depletions have permanently lowered the lake's operating floor. The evidence is in the elevation record: the 1961–1990 baseline average was 4,199.6 ft. The 30-year rolling average is 4,195.9 ft. That 3.7-foot gap did not open because of drought—precipitation and temperature trends account for roughly half of it. The other half—approximately 2 feet—reflects the cumulative effect of depletion growth since the mid-twentieth century: agricultural expansion in Idaho and Utah's Bear River basin, urban growth in the Weber and Jordan basins, and rising M&I demand. In a terminal lake, 2 feet corresponds to a material reduction in surface area, wetland extent, salinity dilution, and ecological function. That chronic depression was in place before the 2021–2025 shock arrived. It set the floor from which the lake fell.
The climate/depletion attribution is derived from the FAQ 11 climate sensitivity analysis, which isolates the climate contribution to the baseline-to-rolling gap; the residual is attributed to depletion growth in the historical record. The Water Ledger holds depletions constant across periods for accounting comparability—the attribution analysis lives in FAQ 11, not in the ledger arithmetic.
This 2-foot human-caused depression is real and consequential. Equally important: because the depletions lowered the starting floor before the 2021–2025 climate shock arrived, the shock produced a lower bottom than it would have from a higher baseline. Depletions did not cause the acute crisis. They made it worse and they will make future climate shocks worse.
The correct statement of human causation is: human depletions have depressed the lake’s operating range by approximately 2 feet from its mid-twentieth century equilibrium. Conservation that durably reduces depletions raises that floor over time. It is necessary and worth doing for exactly that reason.
Conclusion 3: The lake’s response to 2023-2024 was physically correct, not evidence of failure
A widespread interpretation in public discourse held that the lake’s incomplete recovery during the wet years of 2023 and 2024 demonstrated that human depletions had become so severe that even abundant precipitation could not restore the system. This interpretation is incorrect and the data shows why.
The elevation sequence from the beginning-of-water-year record:
- 2021: 4,192.5 ft → 4,190.4 ft (−2.1 ft) terminal flow: 704 kaf
- 2022: 4,190.4 ft → 4,189.0 ft (−1.4 ft) terminal flow: 743 kaf
- 2023: 4,189.0 ft → 4,192.0 ft (+3.0 ft) terminal flow: 2,090 kaf
- 2024: 4,192.0 ft → 4,192.4 ft (+0.4 ft) terminal flow: 1,948 kaf
- 2025: 4,192.4 ft → 4,191.1 ft (−1.3 ft) terminal flow: 1,105 kaf
In 2023, terminal flow of 2,090 kaf—nearly matching the baseline average of 2,317 kaf/year—produced a 3.0-foot rise. The lake responded proportionally and correctly. In 2024, terminal flow of 1,948 kaf—still well above the rolling and shock averages—produced only a 0.4-foot rise. This is not a system failure. It is refill physics.
As the South Arm rises from 4,189 ft to 4,192 ft, volume accumulates efficiently because the lake surface area is relatively small. As the lake rises further, surface area expands rapidly. At 4,192 ft the South Arm covers approximately 396,000 acres. At 4,198 ft, it covers approximately 488,000 acres—a 23 percent increase in evaporating surface. Each additional foot of elevation requires substantially more volume to achieve the same rise because more water is distributed across a larger surface and more is lost to evaporation. The 2024 inflow was therefore absorbed by an expanded lake surface rather than producing proportional elevation gain.
An important additional factor in the differing South Arm responses observed in 2023 and 2024 was east causeway berm management. In 2023 the berm was closed, increasing the elevation differential between the South and North Arms and retaining more water in the South Arm. In 2024 the berm was opened, allowing a significant volume of South Arm inflow to pass into the North Arm and reducing the observed South Arm elevation gain. For short-term analyses, both refill geometry and berm management influence how a given volume of inflow is expressed as South Arm elevation.
The 2012 water year provides the clearest historical illustration of refill geometry. The South Arm began at 4,197.4 ft following the exceptional 2011 flood year, received 1,601 kaf of above-average streamflow, and still fell 1.1 ft because the lake evaporation residual reached 3,338 kaf that year—the highest in the 2003–2025 record—driven by the much larger evaporating surface at the higher elevation. Attributing the incomplete 2023–2024 recovery primarily to human depletions rather than to refill physics is therefore a category error with material consequences for public expectations and policy credibility.
Independent observations from the Zone 2 terminal gages reinforce this interpretation. Data from Farmington Bay Causeway and Goggin Drain confirm the Zone 2 capacitor effect during the 2023 recovery sequence. In water year 2023, Zone 2 Jordan delivery exceeded Zone 1 inflow by 225 kaf as groundwater stored during the drought recharge period discharged to the open lake, amplifying the lake’s response to the wet pulse beyond what Zone 1 inflow alone would predict.
Conclusion 4: The 4,198-foot target by 2034 requires favorable climate—the current Bankable portfolio is insufficient on its own
The total system volume required to raise the lake from 4,192 ft to 4,198 ft is 4,429 kaf, derived from Casey-Root bathymetry. Distributed over the eight water years from 2026 through 2033, this requires a refill component of approximately 554 kaf/year above equilibrium inflow. The structural flow gap—the difference between the inflow required to maintain 4,198 ft under 30-year average climate conditions and the current 30-year rolling inflow—is approximately 200–400 kaf/year, with 300 kaf/year as the central estimate (see FAQ 11). The total annual deficit that must be closed and sustained to reach 4,198 ft by 2034 is therefore approximately 854 kaf/year. This must be maintained for eight consecutive years.
This figure is derived from two ledger quantities: the inflow required to maintain 4,198 ft under 30-year average climate conditions (approximately 2,200 kaf/year, from the equilibrium relationship at that elevation in the Casey-Root bathymetry and baseline evaporation rate) minus the current 30-year rolling inflow estimate (approximately 1,900 kaf/year, from the 1996–2025 gage record scaled by the 0.8246 factor). The derivation is shown explicitly in the Water Ledger gap-to-close tables. The 300 kaf/year figure should be read as an order-of-magnitude structural estimate—it is sensitive to assumptions about evaporation at 4,198 ft and the rolling inflow period—rather than a precisely measured quantity. The 200–400 kaf/year range describes uncertainty in the structural Flow Gap; it is not an estimate of the current Bankable water portfolio.
The completed order-by-order reconciliation of the currently tracked dedicated-water portfolio produces estimated annual Bankable lake accretion of approximately 119.707 kaf/year under wet-regime conditions and 158.515 kaf/year under dry-regime conditions—reasonably summarized as approximately 100–200 kaf/year. These figures represent the currently quantified portfolio, not a ceiling on all conservation or restoration actions that might be developed in the future. The portfolio’s 193.718 kaf of fixed-order maximum associated with unquantified actions and its 549.456 kaf active fixed-order maximum are not included as annual Bankable lake-accretion estimates.
Against the central 854-kaf/year requirement, the currently quantified portfolio leaves approximately 695–734 kaf/year not presently covered by demonstrated Bankable actions. Closing that residual would require substantial additional Bankable mechanisms beyond the current portfolio, favorable climate producing additional basin yield, or both.
The 2026 Strike Team’s own modeling confirms the scale of the challenge. Even under the maximum scenario of an additional 800 kaf/year of inflow sustained from 2025, the mean simulated lake elevation in 2034 is 4,196.9 ft—still 1.1 ft below the state’s 4,198 ft management benchmark. Under that same scenario, the Strike Team identifies 2055, not 2034, as the realistic planning horizon for achieving 4,198 ft.
Under the currently quantified portfolio, reaching 4,198 ft within the stated timeline would still require multiple consecutive above-average inflow years—potentially comparable to the 1982–1986 sequence that produced the historic high—unless additional Bankable actions are developed and demonstrated at a scale well beyond the present portfolio. New actions can be pursued; favorable precipitation cannot be engineered.
This conclusion does not argue against conservation. The current portfolio provides material, regime-dependent lake accretion, reduces the remaining system deficit, supports a more durable operating floor, and lowers the amount of favorable climate required. It argues against a public narrative that treats conservation claims, fixed-order quantities, or unquantified benefits as though they were already demonstrated lake accretion—or that implies the current Bankable portfolio alone is sufficient to meet the 2034 target. Maintaining those distinctions is essential to preserving credibility as genuine conservation progress is achieved.
Conclusion 5: The KSLC cross-validation confirms the accounting framework is internally consistent
A key test of any accounting framework is whether its inputs and outputs are mutually consistent when checked against an independent measure. The GSL Accounting framework passes this test.
KSLC Hargreaves-Samani evapotranspiration multiplied by total lake area—derived from Casey-Root bathymetry at average annual South and North Arm elevations—tracks the forced evaporation residual in the annual storage changes table at an average ratio of 1.011 over the 23-year record from 2003 to 2025, with a standard deviation of 0.080. This means a single-station airport ET estimate applied to the full lake surface reproduces the residual evaporation to within 1 percent on average across two decades of widely varying lake levels, inflows, and climate conditions.
This result does three things. It validates the KSLC station as a temporally consistent proxy for basin-scale atmospheric demand despite its limitations as a spatial estimate. It confirms that the evaporation residual is primarily carrying actual open-water and wetland evaporation rather than systematic bias from upstream gage placement or groundwater misspecification. And it demonstrates that the framework’s components—the 0.8246 inflow scaling factor, the Casey-Root bathymetry, the KSLC climate series, and the USGS gage record—are mutually consistent when applied together.
Years 2005 (ratio 0.775) and 2018 (ratio 1.143) represent the expected behavior of the Hargreaves-Samani method in cool-wet and hot-dry extremes respectively. These are method-consistent outliers, not framework errors. The 1.011 central tendency across 23 years is a stronger result than the method deserves on paper and provides a meaningful foundation for the framework’s quantitative conclusions. See FAQ 10 for more discussion.
Conclusion 6: Depletion figures are not comparable across official reports without explicit boundary documentation
The 2026 Strike Team reports total M&I depletions of 640 kaf/year for the Great Salt Lake basin (2020–2024). The Utah Water Budget Model—the Open Data Portal source underlying the Strike Team's basin-level allocations—reports 556 kaf for the same basins and period. The 84 kaf difference is not a boundary dispute: both sources cover the same geographic extent. It reflects methodological refinements in secondary water accounting, specifically the revision of the outdoor depletion factor from 40% to 91%, documented in the Utah Water Budget Handout (updated December 2025). The practical implication is that M&I figures drawn from the WB Model and from Strike Team reports are not directly comparable even when they reference the same basins and time period. This site uses the Strike Team figure of 640 kaf/year as the authoritative total, with basin-level allocation from the WB Model scaled proportionally.
The broader issue is that depletion estimates have changed substantially across successive reports—from the original basin plans through the 2021 Utah Water Plan, the 2023 Strike Team, the 2024 Strike Team, and the 2026 Strike Team—for reasons that include geographic boundary revisions, improved ET measurement, secondary water reclassification, new line items, and updated outdoor depletion assumptions. The 2026 Strike Team acknowledges that the updated water budget shows M&I rising from 16.4% to 26.3% of total depletions, reflecting "improved measurement, not increased use." This is a significant methodological revision that is documented in the 2026 report but not fully explained across the historical series.
The practical consequence: any analysis comparing depletion figures across reports may be comparing incompatible accounting conventions without knowing it. This affects bankability analysis, policy cost-effectiveness calculations, and any model that uses sector depletions as an input. The FAQ page documents the specific sources of variation with a crosswalk table.
Conclusion 7: Dedicated-water policy is building a higher operating floor—but its value must be managed as a regime-dependent portfolio, not summed as a single water number
Applying the Great Salt Lake Accounting Standard (GSLAS) to the complete dedicated-water portfolio distinguishes legal authorization from recurring physical lake accretion. The active portfolio contains 549.456 kaf of fixed order maximums, while the available record supports quantified representative annual bankable-accretion subtotals of 158.515 kaf/year under the dry regime and 119.707 kaf/year under the wet regime. Another 193.718 kaf of fixed order maximum remains unquantified pending measured delivery, reported participation, documented depletion, or a supported counterfactual baseline. The State’s separate 476.115 kaf cumulative DAT balance is an administrative stock accumulated over time, not an annual inflow estimate.
The difference between the dry- and wet-regime subtotals is itself an important managerial finding. Upstream exchanges, agricultural conversions, and imported-water deliveries generally perform best when water and routing capacity are available. Elevation-dependent industrial agreements retain more water as lake elevation declines and withdrawal limits tighten. The portfolio therefore provides different kinds of protection under different conditions rather than one fixed annual quantity.
Not every conserved acre-foot appears immediately as open-lake elevation. Water may first replenish shallow groundwater, wetlands, refuge units, or depleted conveyance reaches. That recharge can restore habitat and hydraulic connectivity and may support later terminal delivery, but it should not be counted as current bankable lake accretion until the physical benefit is attributable and measurable.
This does not make policy action ineffective. Actions that reduce depletion, prevent direct lake withdrawals, improve delivery control, or recharge depleted parts of the terminal system reduce the structural deficit that future inflow must overcome. They can slow decline, support a higher operating floor, and allow more of the next favorable hydrologic regime to reach or remain in the lake.
The managerial conclusion is that dedicated water should be evaluated as a measured portfolio—by physical mechanism, hydrologic regime, control, measurement, and durability. That accounting shows what policy has produced, what remains uncertain, and where better operating records are needed. It also explains why dedicated-water actions remain worthwhile even when their full value does not immediately register as lake elevation.
Key Numbers for Reference
The following values are derived from the datasets, State Engineer orders, and documented accounting analyses published on this site and are provided in this format to support reproducible analysis. The source notes identify the applicable basis for each group of figures. All lake volumes use Casey-Root NGVD29 bathymetry with South Arm, Bear River Bay, and Farmington Bay at the stated South Arm elevation and North Arm modeled one foot below South Arm.
A Note on This Page
The Great Salt Lake has been studied extensively. The USGS maintains continuous elevation and streamflow records. The Utah Division of Water Resources publishes water budgets and basin plans. The Strike Team reports compile depletion figures and policy recommendations. That body of work is the foundation the GSL Accounting framework (gslaccounting.org) builds on, and this framework uses those same public data while applying a different accounting structure and interpretation.
What this page attempts is different in kind. Official sources describe conditions and recommend actions within institutional, legal, and administrative constraints that are real and legitimate. Academic and advocacy sources interpret those conditions through frames that serve their audiences. Neither is well positioned to state plainly what the arithmetic shows when the ledger is closed consistently across time periods and boundary conventions.
The seven conclusions on this page follow from applying a consistent accounting framework to the available public data. They are stated as directly as the data permits. The numbers are reproducible, the boundary assumptions are documented, and the datasets are publicly available on this site for anyone who wants to check the work. Where the data is uncertain or the methodology requires judgment calls—the inflow scaling factor, the treatment of natural ET, the boundary conventions for M&I depletions—those choices are documented on the FAQ page. Reasonable analysts may make different choices. What this framework asks is that any alternative analysis show its accounting work at the same level of transparency.
© 2026 GSL Accounting · Version 1.1 (August 2026). Content may be shared or cited with attribution. Built by humans with AI assistance for data validation and drafting, and grounded in public data; analytical judgments and conclusions are the authors’ own. See the Changelog for revision history and archived change notes.