The Great Salt River Initiative - Pacific Decadal Oscillation

The Great Salt Lake as an externally driven damped oscillator:

The forcing function has been proven to be the Pacific temperature and current circulatory systems described by

the Pacific Decadal Oscillation (PDO) index.

Post-1980 water management has been haunted by a subtle but critical confusion: the assumption that wet oscillation cycles will restore the lake. This assumption is incorrect. The oscillation frequency has not changed. What has changed is the baseline around which oscillations occur. The baseline shifted by approximately -800 kAF/yr

No new wet oscillation cycle, however favorable, can overcome this structural deficit. The 1983-1986 wet period, while impressive, was merely a decadal-scale excursion within the range of quasi-periodic variability. It was not recovery; it was temporary amelioration.

GSL has a characteristic response time (memory τ ≈ 20 years), and external climate forcing at 7-10 year periods drives quasi-periodic oscillations with exponentially decaying amplitude.

The spectral evidence (the clearly oscillating nature of measurable lake volume changes) strongly supports the hypothesis of a driven damped oscillator, where the oscillator is NOT the lake. Standard signal processing approaches can be used to analyze the nature of the oscillation and make several observations:

1. Amplitude varies with climate regime: Oscillations are stronger during cool PDO phases (1950-1976) and weaker during warm phases (1977-1998). A resonator would show constant amplitude.

2. Period varies with PDO phase: 30-year periodicity shifts to 10-year as PDO transitions (circa 1700-1750 and 1977). A resonator would show constant period.

3. Phase lag is consistent with integration: 6-9 year lag between PDO phase transition and GSL response is consistent with the lake's ~20-year integration time.

4. Exponential envelope decays: Without sustained external forcing, oscillation amplitude decays exponentially

The PDO cycle is hotter and drier with a high index value, and cooler and wetter with a low value. Hot cycles correspond to dry cycles and low GSL elevations ~ten years later. This attribute gives us predictability. The PCC refers to the measured elevating ocean temperature referred to as Pacific Climate Change. This effect creates a steady downward pressure on the lake elevation as indicated by the light purple to dark purple (left to right) transition in the figure below.

The 8 year period is FORCED, not intrinsic. It's the deterministic response of a damped closed-basin lake to quasi-periodic forcing from Pacific Ocean systems indexed by the PDO.

The Physics

• Frequency: PDO transitions (7–10 years quasi-decadal period)

• Amplitude & coherence vary with PDO phase (confirms external forcing)

• 20-year memory of GSL acts as low-pass filter

This is where our confidence comes from. Two apparently completely independent models converge: Both say: by 2034, elevation drops to approximately 4183 feet. That convergence is powerful. It means the system is predictable by clear physics.