It is hard to believe that water can change the gravitational field of Earth. However, by using the Gravity Recovery and Climate Experiment (GRACE) satellite, researchers are able to compute the changes in gravity due to changes in the amount of water in an area. This satellite has been measuring the changes in Earth’s gravity since it was launched on March 17, 2002. As part of its Image of the Day, NASA has published a series of images of the changes in gravity due to the changes in seasonal precipitation.
Though it is distributed over the landscape, water has mass; the greater the mass, the greater the gravitational attraction. Blues indicate increases above the normal water storage (mass) for an area, while browns indicate decreases. Water storage changes are measured in centimeters because they are, according to NASA hydrologist Matt Rodell, “expressed as an equivalent water level change, as if all the land’s water were ponded on the surface.”
