Shifting shoreline: A four-decade analysis of coastal spatial transformation in an urban fishing settlement

Abstract

Background: Coastal cities across the Global South are experiencing rapid spatial transformation driven by urbanization, port expansion, and land reclamation. This study examines four decades (1988–2025) of coastal spatial transformation and identifies the critical period in which development trajectories changed structurally. Methods: A quantitative-spatial approach integrating multitemporal remote sensing and non-parametric time-series analysis was employed. Built-up areas were extracted from Landsat 5 TM, Landsat 7 ETM+, and Landsat 8 OLI/TIRS imagery for 1988, 2000, 2015, and 2025 using the Normalized Difference Built-up Index (NDBI) with adaptive thresholding. Structural changes in the time series were detected using Pettitt’s change-point test implemented in the pyhomogeneity module. Findings: Built-up land expanded from 26.43 ha in 1988 to 86.11 ha in 2025, representing a cumulative increase of 225.8%. Three phases of transformation were identified: organic settlement expansion (1988–2000), infrastructure-driven acceleration (2000–2015), and consolidation through densification and small-scale reclamation (2015–2025). The Pettitt test identified a statistically significant change point in 2015 (p ≈ 0.000), after which mean built-up extent increased by 71.1%. Coastal spatial transformation is non-linear and shaped by the interaction of urbanization pressures, infrastructure development, reclamation, and planning policies. Conclusion: The findings highlight the need for socio-ecological safeguards in coastal planning to support Sustainable Development Goal 11 and balance urban growth with the protection of vulnerable coastal communities and ecosystems. Novelty/Originality of this article: This study provides the first statistically dated reconstruction of four-decade coastal spatial transformation by integrating multitemporal NDBI analysis with Pettitt change-point detection, offering a reproducible and low-resource framework for long-term coastal monitoring in data-scarce regions of the Global South.