Trend analysis of the indicators of urban wetland change and its implications using geospatial indices and statistical analysis

Darbhanga City is a major centre for producing fox nuts (Euryale ferox) and water chestnuts (Trapa bispinosa). The city had 300 lakes in 1964, reduced to 83 in 2023. There is a paucity of research on the urban wetlands of the area. The study attempts to bridge the research gap in the area by utilising geospatial indices to calculate NDVI, MNDWI, NDBI, EBBI NDMI, BSI, LULC, and LULCC detection to investigate the impact of land use change on the urban wetlands. Decadal analysis change was conducted using Landsat satellite data for 1989, 2000, 2010, 2020 and 2023, for two seasons: pre- and post-monsoon. EBBI showed better results for bare land area than BSI. Change detection was analysed for four major classes: built-up areas, urban plantations, water bodies, and barren land. The most significant change was observed for the built-up area, which increased from 21.3 % (1989) of the total land area to 59.8 % (2023). The other land use classes have decreased. The Kappa coefficient depicted an excellent overall accuracy of 89 %. The area under a water body in 1989 was 13.2 sq.km, which decreased to 4.2 sq.km in 2023. A common trend can be observed in pre- and post-monsoon results of MNDWI and NDMI. The results showed a positive increment of built-up area and a significant decline in the water body. This could result in a decrease in the production of foxnuts, impacting the livelihood of the local population as well as the water-related sustainability of the city. • This study utilises a multi-sensor approach, to assess LULC changes in Darbhanga city. • Results revealed a significant increase in built-up areas and a concomitant decline in wetlands. • Rapid urbanization poses a serious threat to the city's ecological balance and the community livelihoods.