Shoreline change analysis and trend-based forecasting along the Bushehr coast, northern Persian Gulf

Abstract

This study quantifies multi-decadal coastal-boundary movement and evaluates conditional future-position scenarios along the approximately 9.8 km Jazireh Shomali–Bandar Rig sector of the northern Persian Gulf. Four Landsat waterlines from 1993, 2002, 2013, and 2023 were extracted with the Tasseled Cap Wetness component and analysed with the Digital Shoreline Analysis System across 195 transects spaced at 50 m. Post hoc Otsu thresholds, perturbations of ± 0.01 and ± 0.02 Wetness units, and an independent Modified Normalized Difference Water Index classification were used to evaluate extraction robustness. The 2023 waterline was also compared with a Google Earth line acquired 33 days earlier. Net movement averaged − 264.35 m; mean endpoint and linear-regression rates were − 8.84 and − 10.16 m per year. Using common thresholds of less than − 0.25, − 0.25 to + 0.25, and greater than + 0.25 m per year, endpoint rates classified 127, 19, and 49 transects as erosional, stable, and accretional. Endpoint and regression rates were strongly correlated (r = 0.996; class agreement = 91.8%). Median shoreline displacement caused by ± 0.01 threshold perturbations was 2.81–9.93 m, although upper-tail responses were large over complex wet surfaces. The Google Earth line intersected 130 final transects and had a median absolute separation of 249.78 m, showing that it is not a tide- and date-matched accuracy reference. A diagnostic forecast of 2023 from the first three epochs produced a mean absolute error of 131.74 m and a root mean squared error of 192.77 m. Ten- and twenty-year projections therefore remain exploratory screening scenarios, not engineering design lines. The study contributes a transparent uncertainty audit and identifies monitoring priorities for a data-limited coast.