Better flood forecasts eyed from space

by Timothy Oleson
Tuesday, November 4, 2014

Satellite measurements of total water storage in river basins — including surface waters, snow, groundwater and soil moisture — may help indicate, months in advance, whether those basins will be predisposed to major flooding, according to new research published in Nature Geoscience. Thus, they could help improve on conventional flood forecasts, which are often based on shorter-term weather forecasts combined with incomplete estimates of basin saturation and offer abbreviated lead times for predictions.

From May to August 2011, catastrophic flooding in the Missouri River Basin breached levees, inundated thousands of acres of farmland, claimed five lives and caused an estimated $2 billion in damage, according to a National Weather Service report. Record snowmelt and elevated groundwater levels preceded the floods, which were triggered by heavy rains.

University of California at Irvine scientists looked at data collected by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites — which measure changes in Earth’s gravitational pull due to regional changes in water storage — over the 1.37-million-square-kilometer river basin leading up to and during the summer of 2011. Comparing the satellite data to stream gauge measurements along the Missouri River, John Reager and colleagues correlated total water storage in the basin to river discharge levels, which is representative of how close a basin is to flooding.

With this correlation factored in, modeling indicated that the potential for major flood-like river discharges on the Missouri could have been seen at least five months in advance, and possibly as much as 11 months beforehand, offering more time to prepare for flood-related impacts. Using similar correlations between river discharge and only soil moisture or snow-loading, the same model indicated the potential for major flooding one to two months in advance.

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