Decoding urban sprawl in Nagaon, Brahmaputra Valley: a Shannon entropy and Gini coefficient analysis.

Urban sprawl has emerged as a serious challenge for sustainable planning and development in mid-sized cities of developing countries like India. The study examines the spatiotemporal pattern of urban sprawl in the Nagaon Urban Area (NUA), located on the south bank of the Brahmaputra Valley in central Assam, over the period from 1993 to 2023. The study employed Landsat TM (Thematic Mapper) of 1993 and 2003 and Landsat OLI (Operational Land Imager) of 2013 and 2023. The urban sprawl is assessed using the Gini coefficient and Shannon entropy model. Moreover, landscape matrices have been employed to corroborate the trend of urban growth. The study found that NUA made significant land use and land cover changes (LULC) during the study period. Among all land use categories, the built-up land experienced massive positive growth at an annual rate of 0.32 sq km. The vegetation cover, on the other hand, exhibited a significant annual decline of 0.47 sq km. The built-up land expanded more in the northern (N), northeastern (NE), and western (W) directions, mostly in zones 2 and 5, demonstrating edge expansion and leapfrog development. The positive trends of ED (edge density), PD (patch density), and LSI (largest shape index) with waning LPI (largest patch index) substantiate urban sprawl at NUA. The rising Shannon entropy value from 4.70 to 5.90 with declining Gini value from 0.71 to 0.55 indicates the dispersed and decentralized urban growth at NUA from 1993 to 2023. The significant negative correlation of - 0.98 between the Gini and Shannon entropy values supports the observation. Thus, the present study provides a new approach to address urban sprawl for effective urban planning.