Spatiotemporal Dynamics of Urban Expansion and Vegetation Cover Using Remote Sensing and NDVI in Mwanza City, Tanzania (2015–2025)

Abstract

Rapid urban expansion can alter vegetation cover and the spatial distribution of urban green spaces. This study examined the spatiotemporal dynamics of urban expansion and vegetation cover in Mwanza City, Tanzania, between 2015 and 2025 using Landsat 8 imagery and a geographic information system (GIS)-based Normalised Difference Vegetation Index (NDVI) analysis. Images acquired in August 2015 and August 2025 were assessed using consistent NDVI intervals to distinguish three categories: built-up areas/bare land, moderate vegetation and dense vegetation. This comparison provides a decade-long assessment of the spatial distribution of the three classes. The findings show thta, the built-up area/bare land category increased from 1,214.46 ha to 1,676.70 ha, a gain of 462.24 ha (38.07%). Moderate vegetation declined from 41,369.59 ha to 39,006.01 ha, a reduction of 2,363.58 ha (5.71%), while dense vegetation decreased from 1,066.05 ha to 506.05 ha, a loss of 560.00 ha (52.53%). The maps show outward expansion of areas with low NDVI values from the urban core and increasingly discontinuous vegetated areas. These patterns indicate that urban growth coincided with reduced vegetation cover, particularly within the dense-vegetation category. The findings provide spatial evidence to inform green infrastructure retention, sensitive hillside and shoreline zoning, and climate-resilient stormwater management in Mwanza City. Interpretation should account for the combined built-up/bare land classification and the two observation dates.