Environmental and human impacts on Bangalore's regional water scarcity

The Arkavathy River Basin adjacent to Bangalore, India, faces a multitude of challenges driven by water demands from urbanization and intensification of agriculture. In the Arkavathy Basin, the two major reservoirs that historically supplied water to Bangalore now receive little to no inflow. Recent research has resulted in multiple plausible hypotheses attributing streamflow reductions in the Arkavathy to (1) increased evapotranspiration due to a boom in eucalyptus plantations and irrigated agriculture, and (2) increased deep drainage from surface soils due to long-term, excessive groundwater extraction. Current knowledge of Bangalore's water scarcity is largely based on anecdotal evidence and the sparse environmental data for this region is insufficient to definitively test these hypotheses. To bridge the gap between provincial and academic knowledge and better understand the nature of regional water resource depletion, we utilize a range of methods to integrate information across spatial and temporal scales. We use the full history of Landsat satellite imagery to approximate post-monsoon water storage in tanks and construct a spatially-explicit, historical record of surface water. We combine stable isotope mixing models, traditional field methods, and kite photography to build a deeper understanding of rainfall-runoff processes. Remote-sensing results confirm reductions of surface water in many of the tanks in the upper reaches of the watershed. We also observe an increase in surface water availability downstream of Bangalore, where imported water results in large waste flows. Field methods reveal considerable contributions of Hortonian overland flow due to soils with low hydraulic conductivity, mitigating changes in the subsurface water balance. We conclude that surface water availability is strongly related to spatial patterns of urban and agricultural water demand overlaid on a template defined by topography, soil, and climate.