Artist's conception of the twin Grace satellites in the Earth's orbit

Gravity-sensing satellites to provide early flood warning

Earth-observing satellites could provide warning of river flooding months in advance, a study has shown.

In a paper published in Nature Geoscience, a group of American researchers examined data about the region around the Missouri river which had been struck by catastrophic flooding in 2011.

The data captured by two satellites of the GRACE (Gravity Recovery and Climate Experiment) constellation enabled the team to analyse sources of river basin wetness including surface and ground water, snow and soil moisture prior to the catastrophic floods.

Reviewing the information available, the team concluded they could have predicted the catastrophic floods up to 11 months in advance.

The Grace constellation is a joint project of Nasa and the German Aerospace Centre focusing on measuring tiny differences in the Earth’s gravity caused by the uneven distribution of mass around the planet.  

"Basin-scale estimates of water storage derived from satellite observations of time-variable gravity can be used to characterise regional flood potential and may ultimately result in longer lead times in flood warnings,” the US team wrote in the Nature Geoscience article.

"We show that the inclusion of Grace-based total water storage information allows us to assess the predisposition of a river basin to flooding as much as five - 11 months in advance."

Conventional field measurements of snow water and soil moisture were only useful indicators up to two months in advance of a flood.

Further studies of flooding affecting the Columbia River in North America and Indus River in Pakistan confirmed the accuracy of Grace-based predictions.

The twin Grace satellites circle the Earth 15 times a day, sensing minute variations in the planet's gravitational pull.

When one satellite passes over a region of slightly stronger gravity, it is pulled slightly ahead of the other. In this way, tiny fluctuations in gravity can be measured.

The 2011 Missouri flood was a one in 500-year event that occurred when two storm systems dumped a huge amount of rain on a region already saturated by a record snow melt.

In May of that year the region was declared a federal disaster area.

An estimated 130,000 acres of Missouri farmland were inundated, major interstate roads washed away, railways swamped, and dams disabled. The cost of patching up levees and repairing dams alone was estimated at more than a billion dollars (£590m).

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