Long-term monitoring of cropland transformation in Kolkata Metropolitan Area, India using open-source geospatial technologies

Urban and peri-urban agricultural practices are degrading throughout the developing world owing to unprecedented urban sprawling and consequent expansion of built-up areas. This study attempted to assess the changing land use/land cover patterns of Kolkata Metropolitan Area, India from 1990 to 2020 with special emphasis on the transformation trajectories of its urban and peri-urban agriculture as a case study using free and open-source software and multi-temporal geospatial database. It also aimed to project the transformation scenario of croplands in 2030 through application of the artificial neural network algorithm of the freely available Modules for Land Use Change Evaluation plugin. Results revealed a persistent spread of built-up areas by engulfing croplands, wetlands, vegetation and water bodies throughout the assessment period. An overall loss of 181.11 sq. km of croplands between 1990 and 2020 was estimated and found to be more prominent in the northern, eastern, and south-eastern parts of the study area. If the existing socio-economic framework and administrative mechanism would prevail as usual, then the projected land use patterns of 2030 would predict a further decrease of 15.46 sq. km in cropland area thereby culminating to a total 37.39% of it original extent since 1990. A theoretical three-stage model of land use conversion was developed from the empirical results as well as field observations and validated with the findings of the projected scenario. It indicated two primary conversion patterns for the study area, viz. (1) natural area to cropland to fallow land and then to built-up, and (2) natural area to fallow land to built-up. Few necessary management measures were suggested to mitigate this persistent loss of croplands and other natural areas.