Urban Expansion Amplifies Hydro-Saline Processes and Infrastructure Vulnerability in an Arid Coastal City: A Long-Term, Field-Calibrated Remote-Sensing Assessment
In arid coastal environments, urban expansion alters land–water interactions, leading to increased soil salinity and moisture accumulation across urban landscapes. This study examines the spatiotemporal evolution of soil salinity and moisture, and land-use/land-cover (LULC) changes in Port Sudan, an arid coastal city that experienced rapid expansion from 2008 to 2024. The limited vegetation cover enables effective shortwave infrared (SWIR)-based assessment of salinity and moisture, facilitating multi-temporal analysis of LULC change and hydro-saline impacts. The findings demonstrate significant landscape transformation driven by urbanization, with built-up areas nearly doubling, substantial rangeland expansion, and a pronounced reduction in bare ground. These land-use transitions are accompanied by a marked inland expansion of salinity and moisture-affected areas, increasing from 8.12 to 40.36 km2 and from 120.15 to 245.49 km2, respectively, particularly within low-lying and reclaimed sabkha terrains. Urban growth exhibits strong correlations with hydro-saline intensification (R2 = 0.77 and 0.82), as increased surface impermeability and disrupted drainage promote salt accumulation and subsurface water retention. Field observations in representative urban areas confirm that persistent hydro-saline ground conditions are linked to salt crust formation, sustained surface moisture, and progressive corrosion of building materials and foundations. Time-series forecasting indicates that continued urbanization is likely to further extend hydro-salinity-affected areas through 2040, with projections suggesting a substantial spatial increase under current development trajectories, although with uncertainty related to environmental variability and temporal resolution. Overall, this study presents a field-calibrated, earth observation-based framework that connects urban expansion with hydro-saline processes and related coastal infrastructure vulnerability, supporting risk-informed planning and management in arid coastal regions. Salinity and Moisture indices successfully mapped across 16 years using multi-sensor datasets. Integrated remote sensing and VES-EC calibration for semi-quantitative salinity assessment. New calibrated SI threshold (110) derived from EC-RS regression and field evidence. Inland expansion of saline and moist soils is linked to rapid urbanization and surface modification. Predictive modeling shows saline-affected areas may exceed 150 km2 by 2040 without mitigation. This graphical abstract demonstrates that rapid urban growth in Port Sudan, a dry coastal city, intensifies hydro-saline processes and increases infrastructure vulnerability. The study employs multiple data sources, including satellite imagery, MODIS land-use records, fieldwork, and electrical resistivity measurements, to provide a comprehensive assessment of soil salinity and moisture dynamics. All datasets are synchronized using atmospheric correction, temporal normalization, and surface reflectance standardization to ensure consistent analysis across 2008-2024. The analytical framework extracts salinity and moisture indicators (SI, NDMI/SMI, LST, LSE) and integrates them with land-use and land-cover (LULC) classification to quantify changes in built-up areas, bare ground, and rangeland. Calibration using 24 Vertical Electrical Sounding points and 6 solar salt sites establishes salinity (SI > 110) and moisture (SMI > 140) thresholds, enabling semi-quantitative interpretation of hydro-saline intensity. The resulting maps reveal an inland expansion of salinity and moisture from coastal sabkha into reclaimed and peri-urban areas, closely associated with increased impervious surfaces and modified drainage patterns. The graphical abstract shows strong correlations between urban expansion and increased salinity and moisture, confirming land-use transformation as a primary driver of hydro-saline intensification. ARIMA time-series modeling projects these trends through 2040, indicating continued expansion of built-up and salinity-affected areas. The final panel links these environmental changes to field observations of salt crusts, waterlogging, corrosion, cracking, and structural deterioration, emphasizing their impact on infrastructure stability.
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