Malaysian Journal of Geosciences (MJG)

Dhaka the capital city of Bangladesh has experienced a steady loss of waterbodies over the last few decades due to unsustainable urbanization and climate change. This study employs remote sensing and geospatial technology to investigate the spatial-temporal changes of waterbodies of Dhaka city over a 30-year period. This study relied, primarily, on the Normalized Difference Water Index (NDWI) method for the identification and classification of the waterbodies (and non-waterbodies) followed by change detection and accuracy assessment. In addition to this NDWI approach, a supervised LULC classification -followed by change detection has been undertaken for the evaluation of the spatial and temporal dynamics of the LULC classes(Bare Land, Built-up Area, Vegetation and Waterbody). The results of the NDWI-based assessment primarily demonstrate that the extent of the waterbody area has disappeared significantly, from 84.19 km2 in 1992 to37.20 km2 in 2022. This indicates that more than half of the waterbody area has been lost over these 30 years. The overall classification accuracy was 88%, 92% and 90% respectively for the study years 1992, 2007 and2022, with kappa values of 0.84, 0.88 and 0.86 for each respective study year. The supervised LULC classification and change detection present a dynamic picture of the LULC transition, which reveals that the growth of built-up areas is the principal driver leading to the loss of 15.083 km² of waterbodies and 27.483km² of vegetation over the study period. Finally, based on the findings, this study provides a briefing on the likely reasons underlying this dynamic LULC transformation as well as plausible policy strategies to reverse the trend. The findings of this study could be useful to policymakers for the long-term planning and management of urban water resources as well as sustainable urban planning and environmental management of this capital city.