Analysis of the Tolt River Future Snowpack
Event-Based Assessment of Mid-Winter Melt, Climate Variability, and Warming Impacts
Snowpack in the Pacific Northwest is undergoing rapid transformation under climate warming, with important consequences for water supply, flood risk, and ecosystem sustainability. In rain–snow transition basins such as the South Fork Tolt River, changes in snow accumulation, melt timing, and mid-winter ablation are expected to fundamentally alter hydrologic regimes.
This repository focuses on the future evolution of snowpack in the Tolt River basin, using an event-based analytical framework to examine how mid-winter melt events, ENSO-driven climate variability, and warming scenarios jointly influence snow water equivalent (SWE) and streamflow dynamics. Rather than relying solely on peak SWE or seasonal averages, this work explicitly analyzes discrete winter melt processes that are likely to intensify under future climate conditions.
The South Fork Tolt River watershed supplies a substantial fraction of Seattle’s municipal water and hydropower needs. Much of the basin lies within the rain–snow transition zone, making it particularly sensitive to warming-induced shifts in precipitation phase and winter ablation.
- Winter ablation is increasing due to higher temperatures and more frequent rain-on-snow (ROS) events
- Mid-winter melt can significantly reduce peak SWE and advance runoff timing
- Large-scale climate modes, especially ENSO, modulate these processes on interannual timescales
Understanding how these mechanisms interact is essential for anticipating future snowpack conditions, rather than extrapolating from historical April 1st SWE metrics alone.