Spatiotemporal analysis of the ecological decline in Chattogram city amid rapid urbanization: a remote sensing approach

Chattogram City Corporation (CCC), Bangladesh’s second biggest metropolis and major port area, faces environmental degradation due to tremendous urbanization and human activities. The objective of this study was to identify the changes in spatiotemporal features of ecological quality because of the influence of the city spread in the CCC between 2011 and 2023. Ecological indices e.g. Normalized Difference Vegetation Index (NDVI), Land Surface Moisture (LSM), Normalized Differential Build-up and Bare Soil Index (NDBSI), and Land Surface Temperature (LST) were integrated for a Remote Sensing-Based Ecological Index (RSEI). Index values ranging from 0 to 1 were classified into five equal interval classes (Bad, Poor, Moderate, Good, and Excellent). To assess and compare the emerging hotspots in the surrounding regions, the Urban Expansion Intensity Index (UEII), Annual Urban Expansion Rate (AUER), and Urban Expansion Differentiation Index (UEDI) were calculated using Landsat imagery. Ecologically bad and poor regions together in CCC increased from 50.01% in 2011 to 58.32% in 2023. According to RSEI change dynamics, 6237.14 hectares of land were ecologically damaged whereas 2693.66 hectares of land had experienced enhanced ecological condition, suggesting a concerning deterioration of ecological quality in the area. Kotwali thana showed the highest AUER rate of 4.01% in comparison to other urban hubs between the designated time frame. In contrast, Patenga shows lower expansion rates of 1.77%. Moreover, Kotwali has the greatest UEII (1.67) and UEDI (1.06). This implies significant stress from urbanization and development in this area. The analysis of Moran’s I index values for CCC states a general pattern of decreased spatial clustering. Understanding the transitions between different ecological quality classes and combining UEII and UEDI provide targeted locations that need actions to control rapid growth or promote development.