Green space dynamics in response to rapid urbanization: Patterns, transformations and topographic influence in Chattogram city, Bangladesh

Abstract

Green spaces have become an essential part of urban development due to the numerous ecosystem services they provide. Rapid urbanization in developing countries like Bangladesh has created enormous pressure on green spaces. The study investigated the changing pattern of green spaces resulting from unplanned urbanization in Chattogram city and how the topographic gradients of elevation and slope influence the change. Landsat TM and Landsat OLI data from 1990, 2000, 2010, and 2020 were used to produce land use/land cover maps. ASTER digital elevation model was used to derive topographic attributes of elevation and slope. Supervised image classification with maximum likelihood classification algorithm was applied for land use/land cover classification using ArcGIS 10.3. Five land use/land cover types were identified with an overall accuracy of 90% and kappa statistics of 87.3. Changes along topographic gradients were assessed in the GIS environment using overlay analysis. The results show that area coverage of green spaces decreased from 68.34% in 1990 to 36.51% in 2020. The study found a decrease in all green spaces- forest cover (9.9%), agricultural land (7.6%) and vegetation cover (14.3%) from 1990 to 2020. The decrease of green spaces was mainly due to the expansion of built-up areas, about 51.32 km2 area of green spaces were transformed into built-up areas during the period. The changes mostly occurred along low to moderate elevation (0–26 m) and gentle to moderate slope (0–15%) gradients. Green spaces decreased along all topographic gradients but the decreasing trend of forest cover was relatively low in high to very high elevation (26–88 m) and steep to very steep slope (15–66%) gradients. Such a setting can be used to expand forest cover in areas with similar topographic conditions. Built-up areas increased along all topographic gradients, increasing the risk of land degradation. The study has the potential to provide practical information to the local planners for sustainable land use management in Chattogram city.