Predicting impact of urbanization on water resources in megacity Delhi

Rapid urbanization to accommodate the migrating population towards urban centers in several regions of the world is burdening regional water resources. In order to efficiently manage the supply demand gap, which is getting worse with ongoing climate change, we must understand how urbanization is affecting the water availability. Urbanization is represented by an increase in impervious area, which when related to secular changes in water availability, can help us predict the future water stress. In this study we analyze the impact of urban land-use change on Delhi's water resources during time-period 2005-2016 and in future year 2031. Using Monte-Carlo simulations in Land Change Modeler (LCM), we predict the future LULC for year 2031 which exhibits similar pattern of LULC change as observed during 2005-2016. An increase of 36.49% in urban area is observed during time-period 2005-2016 and an increase of 14.05% is predicted during 2016-2031. Using in-situ groundwater measurements, the groundwater abstracted (18.75%) is found to be greater than the amount of total groundwater recharge (14.67%). Using statistical relationship, the groundwater recharge by rainwater, artificial recharge and total recharge are found to influence Delhi's groundwater availability. Also, it is estimated that a 1 km(2) increase in built-up area will decrease 0.3 million cubic meters of groundwater recharge by rainfall. This indicates an alarming future as an increase in urbanization is predicted for future in Delhi. A comparison of GRACE and in-situ data shows that both exhibit a positive correlation of 0.60 and the linear trend derived from GRACE is 2.24 cm/year and that from in-situ data is 2.68 cm/year. This indicates Delhi as water-stressed region. Such an analysis requires in-situ groundwater measurements and since, it is not readily available for every city; we have demonstrated that using GRACE satellite observed water storage change can be a viable option in in-situ data scarce regions. This study demonstrates and predicts impact of urbanization on water availability for Delhi and presents a road map to assess future water availability in various megacities across the globe.