ABSTRACT:

This resource provides the data presented in the Planning for an Uncertain Future section of the "Great Salt Lake Strike Team Data and Insights Summary". (2025, January 17). https://d36oiwf74r1rap.cloudfront.net/wp-content/uploads/2025/01/GSL-Jan2025.pdf. https://gardner.utah.edu/great-salt-lake-strike-team/.

1000 simulations of potential lake levels for the next 30 years were produced for each of four scenarios. The data presented is a statistical summary of these scenarios. Scenarios were developed by David Tarboton at Utah State University.
The scenarios are as follows:
- Baseline scenario assumes no additional inflows to Great Salt Lake. Inflows are randomly sampled from historical data between 2000 and 2024.
-·Additional 250 KAF/year inflow scenario considers an additional 250 thousand acre-feet (KAF) of inflow each year to the lake from water conservation or other sources.
- Additional 375 KAF/year inflow scenario considers an additional 375 thousand acre-feet (KAF) of inflow each year to the lake from water conservation or other sources.
- Additional 770 KAF/year inflow scenario considers an additional 770 thousand acre-feet (KAF) of inflow each year to the lake from water conservation or other sources.

To capture hydrologic variability, the model performs 1,000 simulations for each scenario by randomly selecting historical data (annual inflow, precipitation, and evaporation) from known values between 2000 and 2024. The past 25 years were selected to represent the contemporary period with elevated temperatures and decreased inflow to GSL. Projections start in 2024 with the lake at a level of 4192.1 ft and extend to 2054. The additional inflow scenarios were produced by adding the corresponding value to historical inflow data.

The values chosen represent approximately 10% conservation (250 KAF/yr), 15% conservation (375 KAF/yr) and a conservation or additional inflow value calculated to have the mean lake elevation across the 1000 simulations achieve a level of 4,198 feet by 2054 (770 KAF/yr). These are total basinwide additional inflow amounts without considering the source of the conservation required for them to be achieved.

The results show differing mean values for each scenario, with significant variability within each scenario. The resulting lake elevation in 2054 for each scenario are as follows:
- Baseline: 0.7-foot decline in lake elevation (from 4,192.1 to 4,191.4 feet)
- Additional 250 KAF/year inflow: 1.8-foot lake elevation rise (to 4,193.9 feet)
- Additional 375 KAF/year inflow: 3.0-foot lake elevation rise (to 4,195.1 feet)
· Additional 770 KAF/year inflow: 5.9-foot lake level rise (to 4,198 feet)

The model output data in this resource include the mean, median, minimum, maximum, 5th percentile, 95th percentile, 25th percentile, and 75th percentile values for each simulation. The mean and median are measures of central tendency. The percentile values characterize the probability distribution representing the variability across the 1000 simulations. Given that we used 1000 simulations, both the minimum and maximum values represent extreme situations with a probability of occurrence of 1/1,000, or a 30 year period that might be expected to occur statistically only once in 1,000 thirty year periods, or once in 30,000 years.