Sea Level Rise Modeling in Wigi: Assessing Vulnerabilities and Adaptation Strategies*

Wigi (Humboldt Bay) faces some of the highest sea level rise (SLR) rates on the U.S. west coast due to climate change and land subsidence. This study presents a modeling framework to assess vulnerability in the Eureka/Arcata Corridor of Highway 101, a key transportation route in Humboldt County. Using an existing Humboldt Bay EFDC model and 75 years of tide gauge and wind data, we estimate water levels (still water levels and local wind setup). The 2-D SWAN model simulates wind-generated wave propagation across the Humboldt Bay, and wave runup is estimated empirically. Combining water levels and wave runup, we calculate total water levels and estimate extreme recurrence intervals by fitting to the Generalized Pareto Distribution method. Simulations are run for various SLR and adaptation scenarios, including a nature-based salt marsh project (NBP). With 30 cm of SLR and no adaptation, overtopping occurs monthly, while the NBP offers protection up to a 10-year extreme wind event. With 1 meter of SLR, the NBP shoreline becomes vulnerable to common storms. Our framework offers rapid predictions of extreme water level recurrence and associated uncertainties, for improved planning.