Sustainable groundwater management for large aquifer systems: Tracking depletion rates from space

Nearly 2 billion people worldwide rely on groundwater as their primary source of water for domestic and agricultural use. However, in many regions around the globe, groundwater supplies are being stressed to their limits by overuse, population growth and climate change. Likewise, groundwater quality is also threatened by contamination, land use change, salinization, and in coastal regions, seawater intrusion. In the developed world, water management efforts to minimize the impacts of these multiple stressors on groundwater quantity and quality are complicated by a number of institutional, political and socioeconomic barriers. These include the lack of sufficiently dense monitoring well networks, disparate sampling, data reporting and archiving strategies, inadequate data sharing policies, and in many regions, the lack of groundwater use reporting requirements. In the developing world, such management strategies, if they exist at all, are rudimentary or in their infancy. In this paper, a satellite- based method for characterizing groundwater storage changes in large aquifer systems is described that provides new opportunities for water resources monitoring, particularly in data sparse regions. Two case studies of groundwater depletion are presented, one in the relatively data- rich Central Valley aquifer of California (USA) and in the other in more data- poor northern India. The approach uses observations from the NASA Gravity Recovery and Climate Experiment (GRACE) mission, along with varying amounts of supplementary hydrologic data as available. This method can be applied to large aquifers (>200,000 km2) at monthly and longer timescales with sufficient accuracy to inform regional water management decisions. The approach could also be implemented globally to track changes in the availability of the world’s fresh groundwater resources.