Example of calibration and validation of CoSMoS-COAST using historical satellite-derived shoreline data

An example of calibration and validation of CoSMoS-COAST using historical satellite-derived shoreline data. The figure shows the extent of the CoSMoS-COAST U.S. South Atlantic Coast model transects (panel A—in green) with a zoomed in section of Cape Hatteras, North Carolina (panel B), which shows a close-up of the 50 m transect spacing (green lines). Panel C shows hindcasted and projected wave (blue line) and sea-level rise conditions (orange line) applied to the model at transect #25990 (i.e., the thick green line in panel B). Panel D shows the modeled shoreline position (red line) and its parametric uncertainty (pink bands), which are calibrated (from 1990–2015) with satellite-derived shoreline observations (blue circles) and their confidence intervals (blue ‘whiskers’). Later in the simulation, during the model “hindcast (validation)” period (2015–2020), data assimilation is turned off, and the calibrated model is compared to satellite-derived shoreline observations (blue circles) to assess the model’s structural uncertainty (±2εRMSE, where εRMSE is the model root-mean square error (RMSE) calculated using Eq. (2) and is shown in yellow confidence bands), which is propagated forward with a constant width during the model ‘projection period’ (2020–2100). Note that anomalies in shoreline position during the “hindcast (validation)” period, e.g., the accretion spike in 2017–2018 in panel D (caused by a beach nourishment), generally increase the model’s structural uncertainty (yellow bands) relative to the parametric uncertainty (pink bands). (Basemap from Matlab/Earthstar Geographics/Maxar).