Water Quality Indices and Impact of Land Use/Land Cover Changes on Freshwater System in Ibadan North-West, Nigeria Using Remote Sensing Techniques

The degradation of freshwater systems due to rapid urbanization has become a critical environmental concern in many developing urban centers. Assessing the spatial and temporal dynamics of land use/land cover (LULC) changes is essential for understanding their implications on surface water quality. This study assessed water quality indices to examine the impact of land use/land cover (LULC) change on the freshwaters in Ibadan North-West, Nigeria, using remote sensing techniques. Landsat-7 ETM+ (2014) and Landsat-8/9 OLI/TIRS (2023) imagery were analyzed to assess spatio-temporal LULC changes and extract water indices. Water quality was assessed using the Normalized Difference Water Index (NDWI) and Modified Normalized Difference Water Index (MNDWI). Over a period of 9 years, water bodies declined from 89 to 9 hectares, and vegetation cover reduced from 1,315 to 359 hectares. In contrast, built-up areas expanded from 1,450 to 2,486 hectares, reflecting intensified urbanization. The MNDWI values in 2014 ranged from − 0.3687 to 0.0744, while in 2023 they declined to -0.2282 to -0.0129. NDWI values, already negative in 2014 (ranging from − 0.3430 to -0.2812), declined further in 2023 (ranging from − 0.0101 to -0.0612). These shifts reflect a diminishing presence of strong water signals across both years. Change detection further reveals that NDWI recorded a total water loss of 368.38 ha, while MNDWI showed a smaller loss of 77.21 ha. The contrast highlights that while NDWI detected broader signals, including turbid and mixed-pixel zones, MNDWI more accurately delineated freshwater systems by suppressing noise from surrounding land covers. The findings reveal a substantial reduction in both the extent and spectral quality of freshwater systems over the 9-year period, driven by land conversion and urban encroachment.