Index-Based Change Detection, Spatial Zoning and Environmental Criticality of Urban Land Cover: A Spatiotemporal Study on Gazipur Sadar Upazila of Bangladesh

Urbanization has become a comprehensive phenomenon worldwide as well as in Bangladesh. This study has tried to analyze the urban land cover change pattern of Gazipur Sadar Upazila between 2001 and 2021. This study also has made an investigation to classify the urban land cover of Gazipur Sadar Upazila based on categorical spatial zoning and analyze how urbanization affects nearby green spaces to monitor environmental criticality. Multispectral Landsat satellite imageries, population census data, air quality index, and open-ended questionnaire data were used as the operational data. Spectral indices such as NDVI, and IBI, were performed from remotely sensed satellite data. NDVI was used to extract green cover and IBI was used to extract the built-up area. Spatial zoning was done based on existing literature, expert interviews, and RS analysis. Environmental criticality was analyzed by correlating population density and air quality data with the extracted green cover. Between 2001 and 2021, the built-up area expanded by around 77.7 km2 and green cover by about 74.79 km2. Although the green cover flourished, it decreased in Tongi and Konabari. Besides, the south-western region of Gazipur experiences rapid growth in built-up areas. Three classified zones e.g., industrial and manufacturing zone, forested zone, and neutral zone were extracted from criteria-based spatial zoning. The results of green space per capita analysis showed that from 2001 to 2021, green space in the study area decreased by 10-713 m2. Environmental criticality analysis illustrated that in 2001, two regions (Tongi and Konabari) were classified as highly critical, and by 2021, this number had escalated to five (Tongi, Konabari, Kasimpur, Basan, Gaccha). Furthermore, the study uncovered that the criticality in urbanized areas is growing rapidly.