Urban Growth at the Edge of Limits: Assessing Land-System Change, Biosphere Integrity, and Freshwater Stress in Greater Accra through the Planetary Boundaries Framework

Abstract

This study examines environmental transformation in Greater Accra between 2000 and 2020 through selected dimensions of the Planetary Boundaries framework, with attention to land-system change, biosphere integrity and freshwater stress. The analysis used Landsat 7 satellite imagery obtained from the United States Geological Survey, together with district shapefiles from the Ghana Open Data Initiative. A descriptive longitudinal design was adopted, and the imagery was processed in ArcMap and ENVI 5.1 using image pre-processing, gap filling, calibration, layer stacking, supervised classification, Normalised Difference Vegetation Index (NDVI) analysis and post-classification change detection. The study was conceptually informed by the Environmental Kuznets Curve, Ecological Modernisation Theory and Planetary Boundaries Theory. Results indicate marked land-use and land-cover transformation over the two decades. Built-up land increased by 102.3%, while water bodies, grassland and dense forest declined by 77.7%, 87.3% and 75.7%, respectively. The reduction in vegetated surfaces suggests pressure on biosphere integrity, while the contraction of surface water bodies indicates growing freshwater-related stress. The combined pattern of urban expansion, vegetation loss and declining water coverage points to increasing pressure on selected planetary boundary dimensions within Greater Accra. The findings suggest that population growth, infrastructure development and land conversion are important drivers of ecological change in the region. By connecting observed land-cover dynamics to threshold-oriented sustainability thinking, the study offers context-specific evidence for urban environmental planning in a rapidly changing metropolitan region. It concludes that urban growth in Greater Accra requires stronger spatial planning, improved enforcement of land-use regulations and greater integration of green infrastructure and nature-based solutions to support development within ecological limits.