Geospatial analysis of soil salinity dynamics: Exploring topographic and vegetation influences in coastal Bangladesh

• Vegetation is moderately affected by soil salinity. • Moisture content strongly influences soil salinity. • Salinity increases southward, making the southern region a salinity hotspot. • Elevation influences salinity most; slope, aspect, and TWI have minimal impact. • Vegetation indices show moderate negative correlations with salinity. Soil salinity is a critical environmental challenge within coastal systems, posing a significant threat to vegetation in the territory. This study investigates the spatial distribution of soil salinity in coastal Bangladesh and its relationships with topography and vegetation indices. Seventy-five soil samples (0–15 cm depth) were collected using a stratified random sampling method. Moisture content, electrical conductivity (EC), pH, and temperature were all measured utilizing electrical sensor-based optimized tools. Topographic parameters including elevation, slope, aspect, and topographic wetness index (TWI), were derived from the Digital Elevation Model (DEM) using ArcGIS. Sentinel-2A imagery was utilized to analyze salinity–vegetation interactions through spectral indices such as CRSI, GARI, NDVI, GNDVI, GDVI, and NDI. Results showed that soil salinity ranged from 0.68 to 25.88 dS/m, averaging 6.08 dS/m. A strong positive correlation was observed between soil moisture and salinity ( r = 0.87). Hotspot analysis revealed the southern region as a salinity hotspot, indicating a north-to-south increasing salinity gradient. Furthermore, linear regression showed a strong negative relationship between elevation and salinity ( R ² = 0.91) in regions above 15 m, while slope, aspect, and TWI were insignificant. Vegetation indices, NDVI, and CRSI demonstrated moderate negative correlations with salinity, indicating that higher salinity leads to lower plant health. This study underscores the pivotal influence of topography, especially elevation, on soil salinity distribution and demonstrates the effectiveness of vegetation indices for salinity monitoring. These findings support the use of precision agriculture and informed land-use planning to enhance sustainability and resilience in Bangladesh’s salinity-affected coastal regions.