Ground water storage changes. Global map of changes in the ground water stores around the world as mapped by observing variations in the Earth's gravitational field. Orange areas are where ground water has decreased, and areas in blue are where ground water levels have increased. This data shows the results as of April 2015 relative to a 2002-2015 mean. The data was acquired by the GRACE (Gravity Recovery and Climate Experiment) satellites operated by NASA and the DLR (Germany) that are in polar orbit around the Earth. Anomalies in the gravitational field, when compared to previous readings, can be used to monitor changes in ground water levels.