When it comes to predicting flooding, it isn’t just the amount of rain that matters, but also where the excess rain can be stored – if the earth is already saturated the rain has nowhere to go, and flooding follows on.
Scientists are now taking advantage of the fact that saturated earth has a greater gravitational pull, and that satellites can monitor the changes in saturation from day to day. Prof Shin-Chan Han, from the University of Newcastle in Australia, and colleagues measure changes in the Earth’s gravity by monitoring micrometre changes in distance between the two Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellites.
When the satellites approach an area with higher gravitational pull (such as a saturated groundwater reservoir) the lead satellite is tugged forward, increasing the gap between the satellites. Shortly afterwards the tail satellite is also pulled forward, shortening the distance between the satellites.
By regularly measuring the change in distance between the satellites Han and his colleagues were able to demonstrate that the devastating floods experienced in eastern Australia in March 2021 were preceded by a rapid recharge of groundwater the week before the rains. Their findings, published in Earth and Space Science, have the potential to dramatically improve our ability to prepare for floods.
