A Reclassification-Based Framework for Vegetation Greenness Assessment Across Mixed Landscapes and Spatial Extents

Abstract

Vegetation dynamics are fundamental indicators of environmental health, yet evaluating them in complex, mixed-use landscapes remains methodologically challenging. Traditional statistics are not the real representative of the pixel-level distribution of greenness in a particular area of study, which results in critical disparities in the spatial extent and density of vegetation. To overcome these limitations, this study introduces the Greenness Score (GS), a spatially explicit, area-weighted framework that reclassifies NDVI into ecologically distinct categories to quantify peak greenness intensity and coverage. To test this framework, this study utilizes the NDVI of ten Nigerian cities across diverse bioclimatic zones for the years 2015 and 2025. The analysis shows that traditional summary statistics frequently fail to represent ecological reality. In 2015, Asaba and Ibadan exhibited comparable maximum NDVI values (0.67 and 0.83) and mean NDVI values (0.41 and 0.57), suggesting similar greenness potential. However, the GS analysis exposed a stark contrast in actual biomass: Ibadan supported 175,411 hectares of dense vegetation (56.44% of its area), while Asaba contained only 17.46 hectares (0.06%). The GS framework also shows high performance in detecting temporal shifts invisible to central-tendency measures. Between 2015 and 2025, Asaba’s Average NDVI remained deceptively stable (0.41 to 0.42), masking a significant ecological recovery where dense vegetation expanded from 0.06% to 21.76% of the city. Additionally, Abuja’s Average NDVI declined (0.39 to 0.25), and Abuja lost approximately 112,000 hectares of moderate vegetation. This study reveals that GS provides a more accurate and ecologically meaningful assessment of urban vegetation than traditional summary statistics, highlighting its value for monitoring and managing urban greenness.