Four decades of embayed coastline evolution assessed through the integration of Remote Sensing (CASSIE) and Hybrid Wave Modeling (BinWaves) tools

Abstract

Embayed beaches along rocky coasts exhibit complex shoreline dynamics driven by the interaction between wave climate variability, headland-controlled exposure, and sediment exchange within semi-enclosed cells. This study investigate four decades (1984–2023) of shoreline evolution across 12 embayed beaches along the Santa Catarina coast, southern Brazil, by integrating satellite-derived shorelines, space–time statistical analysis, hybrid wave modeling, and large-scale climate modes. Shoreline positions were extracted from Landsat imagery using the CASSIE-Shoreline algorithm and analyzed through Hovmöller diagrams and transect-based trends to diagnose chronic erosion, dynamic equilibrium, and accretionary behavior. Nearshore wave forcing was reconstructed using the BinWaves hybrid framework, combining CAWCR/CSIRO deep-water hindcasts with SWAN-based nearshore propagation. The resulting reconstruction was validated against available in situ observations. While uncertainties inherent to nearshore wave modeling in complex embayed settings are acknowledged, the approach remains robust for identifying long-term storm-wave patterns. Results reveal a bimodal storm-wave climate dominated by easterly and southerly waves, superimposed on a persistent counterclockwise rotation of the mean storm-wave direction of ~2° over four decades, reaching up to ~5.2° during spring. This directional shift increases wave exposure at northeast- and east-facing embayments, coinciding with a statistically significant increase in storm-wave frequency in these sectors, while south-facing beaches exhibit stable storm occurrence. The Southern Annular Mode (SAM) shows the strongest positive correlation with storm-wave frequency, indicating that SAM-driven variability dominates extreme-wave generation in the South Atlantic. The El Niño–Southern Oscillation (ENSO) exerts a weaker control on storm extremes and likely modulates background hydroclimatic conditions. Decadal reversals in erosion–accretion patterns observed at several south-facing beaches are consistent with large-scale modulation associated with the Atlantic Multidecadal Oscillation (AMO). Together, these results demonstrate that shoreline evolution in embayed systems is primarily governed by climate-driven variability in storm-wave direction, frequency, and clustering, rather than by changes in mean wave conditions. The integrated satellite–modeling approach provides a robust and transferable framework for assessing climate-sensitive coastal morphodynamics everywhere including in data-limited regions.