Abstract:
The assessemnet of the impacts of urbanization on hydrological regime is important as the urbanization affects the water quanity, quality and demand. The impervious surface which is associated with urbanization may increase the flood frequence and magnitude, and decrease groundwater recharge. With the increasing water demand and declining groundwater, the assessment of the impact of increasing impervious surface on groundwater has become important. In this study, an algorithm, named Rule-based Spectral Unmixing Algorithm (RBSUA), is developed to derive annual time series of impervious surface using satellite imagery. The developed algorithm is utilized to derive impervious surface maps for Delhi and adjoining areas during the past 26 years. The impervious surface maps were then utilized with a hydrological model, named WetSpass, to assess the impact on groundwater recharge. The evaluation of the developed algorithm shows that the overall accuracy of the extracted impervious surface varies from 88% to 91% between different years. The result shows that the impervious surface area has increased from 377±78 km2 in 1992 to 708 ±64 km2 in 2017. In addition, the groundwater recharge has declined considerably during the study period. The annual groundwater recharge has decreased from —550 Mm3 to —531 Mm3
between 1994 and 2012. The algorithm developed in this study will help reducing modelling uncertainnity in the future studies. Moreover, the results obtained could be helpful in preparing management strategies for groundwater in the study area.
