Lake Powell is a storage reservoir. Its level is primarily determined by inflows from the Upper Colorado River Basin and releases through Glen Canyon Dam. This chart uses current reservoir conditions and historical inflow years1United States Bureau of Reclamation
Lake Powell Hydrodata Dashboard https://www.usbr.gov/uc/water/hydrodata/reservoir_data/919/dashboard.html1 to project storage forward under fixed release assumptions.
In other words, it asks what Lake Powell storage would look like if the rest of this year’s inflows followed the pattern of earlier years.
How to use this chart
The white line shows the current WATER YEAR to date. The colored lines extend storage forward using selected historical inflow years. Each colored line is one possible path, based on how much water entered Lake Powell in that earlier year from this point forward.
Controls
Water year series selection
The series controls select which historical years to project forward. By default, the chart selects those years whose snow water equivalent is within 20% of this year’s value on today’s date.
Inflow
The inflow control switches between UNREGULATED and ACTUAL. Unregulated inflow estimates how much water would have reached Lake Powell without upstream reservoir operations. Actual inflow shows what actually arrived. For comparing years, unregulated inflow is usually the more useful measure.
Annual Release
The release control sets a fixed annual release target. These options span the most important operating levels in the current Lake Powell framework, from 8.25 million acre-feet down to the current near-term minimum of 6.0 million acre-feet.234 The 6.5 million acre-foot and 5.0 million acre-foot options are included as additional potentially informational projections.
Temperature
In adjusted mode, the shaded envelope applies a temperature-based adjustment to the selected analog inflows from the current date forward. It is meant to show how a warmer or cooler year than the analog might change runoff efficiency.5Temperature-adjusted envelope uses year-to-date basin average temperature differences with low/mid/high sensitivities of 3.5% / 7.0% / 10.5% per °C.
Udall and Overpeck, 2017 https://doi.org/10.1002/2016WR0196385
Lake Powell Storage Projections from Historical Year Analogs
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United States Bureau of Reclamation - Lake Powell Hydrodata Dashboard https://www.usbr.gov/uc/water/hydrodata/reservoir_data/919/dashboard.html Storage, Inflow, and Unregulated Inflow series. ↩︎
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United States Bureau of Reclamation - Colorado River Compact, November 24, 1922. ↩︎
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United States Bureau of Reclamation - 24-Month Study, March 2026. ↩︎
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United States Bureau of Reclamation - Supplement to the 2007 Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead - Record of Decision, May 2024. ↩︎
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Udall, B. and J.Overpeck (2017), The twenty-first century Colorado River hot drought and implications for the future, Water Resour. Res., 53, 2404–2418, doi:10.1002/2016WR019638. ↩︎