IMPACT OF URBANIZATION ON LAND USE AND LAND COVER CHANGE AND ITS IMPLICATION ON DECLINING GROUNDWATER LEVEL AND DRINKING WATER QUALITY

The urban environment continues to expand at an unprecedented rate to meet the demand of increasing global population and economic growth. The expansion of urban areas and resulted changes to landscapes have increased stress to hydrological cycle, biogeochemical processes, and environmental sustainability of natural resources. This study evaluated spatio-temporal changes of land use and land cover (LULC) between 1990 and 2020 in Guwahati city, Assam, India. Time-series Landsat satellite images were classified using supervised classification method (Maximum Likelihood) followed by change detection studies to quantify LULC change over time. Five broad LULC classes were identified on the basis of spectral reflectance signature and visual interpretation. Confusion matrix determined high classification accuracy with Kappa Coefficient >0.81 in all cases. The results showed that the urban built environment have doubled in area in 30 years (1990 to 2020). The increase in urban built environments have resulted at the expenses of vegetation, fallow land/open areas and to some extent wetlands/water bodies. Notably, the expansions of urban areas have taken place from city center to the south, to the south-east, and along the east-west National Highway 37 connecting other NE States of India. The changes in urban environment were largely driven by population growth, economic development and modernization of the city. There is no clear indication of change in the amount of precipitation in response to urbanization during the study period. Analysis of long-term groundwater level data suggests a steady decline in the depth to groundwater level in the areas that have experienced large scale urban development. The declining trend is attributed to the degree of urbanization, decrease in groundwater recharge and over-exploitation of groundwater for domestic and industrial use. The increase in impervious surface cover due to urbanization have played a pivotal role in reduced infiltration and thereby delaying groundwater recharge and increasing runoff. A comparison of fluoride and other water quality parameters based on two-time measurements on different set of wells have shown significant increase in the level of concentrations. A future study is directed to understand how urbanization have influenced geochemical processes and therefore could play an important role to health of millions living within the city.