Gravity variations foretell flood risk months in advance

Small gravitational tugs from waterlogged river basins could give scientists a big advantage in predicting devastating floods, researchers report July 6 in Nature Geoscience.

Hydrologist J.T. Reager and colleagues from the University of California, Irvine looked at data from GRACE, a duo of NASA satellites that detect small changes in Earth’s gravity. As a river basin soaks up water, the satellites record a stronger gravitational pull. Wetter ground is more liable to flood when hit by a surge of rain or snowmelt.

The researchers studied GRACE data collected during the months before the May–July 2011 catastrophic flooding along the Missouri River. The team found that the region’s gravity increased leading up to the floods, and the researchers showed that the uptick could have been used to predict the 2011 flood five months in advance. Field measurements of snowmelt and soil moisture can offer at most two months of warning.

While promising, Reager’s team says the approach can’t predict flash floods brought on by sudden torrential rain, such as the deadly July 2010 typhoon that flooded parts of Pakistan.