Rivers and GRACE...

Source: Science Magazine; US Army Corp of Engineers

When ground water saturates a river basin, the risk for flooding goes up. So does the strength of Earth’s gravity in that region, ever so slightly, because of the extra mass of the underground water. By using tiny variations in gravity detected from space, researchers report online today in Nature Geoscience that they can identify basins that are primed for flooding if additional rains come—sometimes with several months' warning. As a test case, the scientists looked at the gravity signals leading up to catastrophic floods in 2011 on the Missouri River (pictured above). They used data from NASA’s Gravity Recovery and Climate Experiment (GRACE), a pair of orbiting satellites that get tugged around the Earth faster in places where gravity is slightly stronger.

Science Magazine: Gravity measurements can predict river flooding, Eric Hand
UT Austin Climate Science Research: GRACE
NASA: GRACE - Earth Missions