Projected Evolution of Intertidal Habitats in Morro Bay, California Under Sea-level Rise, Climate Variability, and Management Scenarios, 2020-2100

Coastal managers need robust projections of how sea-level rise (SLR), sediment availability, and management actions may alter estuarine habitats. We developed and calibrated WARMER-Coast, an intermediate-complexity modeling framework, to simulate tidal wetland evolution, assess potential upslope migration pathways, and evaluate management scenarios developed in consultation with local stakeholders. WARMER-Coast couples the 1-D soil cohort model WARMER v3 with a simplified 2-D hydrodynamic framework to simulate inundation, sediment transport, surface and edge erosion, plant growth, organic matter accumulation, and carbon storage. Model calibration leveraged extensive field observations, including water-level monitoring, elevation and vegetation surveys, surface elevation table measurements, soil cores, feldspar marker horizons, and short-term sediment deposition measurements. We applied the calibrated model to project marsh and seagrass habitat trajectories across five SLR scenarios and three sediment regimes. Results identify where habitat persistence, conversion, and upslope migration are most likely, and provide a framework for comparing the relative effectiveness of adaptive management actions in Morro Bay and other vulnerable estuaries.