Assessment of wetland and vegetation dynamics in the context of urbanization and seasonal variation using surface indices in Ara city, India

The pressure of rapid urbanisation has led to the rapid transformation of wetlands and vegetation, causing major problems for ecological sustainability in fast-growing cities. This study assesses the spatiotemporal dynamics of wetland, vegetation, and built-up surfaces in Ara City, Bihar, India, from 1995 to 2025 using Landsat 5, 8, and 9 imageries. The following spectral indices were used to assess the seasonal and long-term environmental changes as a result of urban expansion: Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI), Normalized Difference Built-up Index (NDBI), Urban Index (UI), Normalized Difference Bareness Index (NDBal), Bareness Index (BI), and Enhanced Built-up and Bareness Index (EBBI). The anthropogenic impact on vegetation and water resources around Ara city in middle of Bihar-Uttar Pradesh border in Bhojpur district of north-eastern part of Bihar, India surrounding by the Ganga and Son rivers was studied. The results reveal a progressive decline in vegetation cover and open-water features, areas experiencing rapid urban expansion. Pre-monsoon NDVI exhibited lower spatial variability than post-monsoon NDVI, indicating seasonal differences in vegetation dynamics. MNDWI indicated a reduction in water-related features, whereas higher NDWI values in 2025 suggest an increase in water-associated surfaces within the urban landscape. The results of the Pearson’s correlation analysis indicate negative correlation between built-up indices and NDVI and negative correlation between built-up indices and MNDWI, showing the inverse relationship between urbanization and ecological health indicators, while positive correlation between built-up indices and NDWI shows the positive relationship between built-up and water. The study underscores that wetlands, which serve as critical habitats for migratory birds, are increasingly threatened by human activities. The novel nature of the study is the integration of multi-season and multi-index analyses of the dynamics of wetland, vegetation, and urban surfaces over 30 years. The results offer insights for sustainable urban planning, wetland conservation, ecosystem management and may have implications for wetland-dependent biodiversity.