Using AMSR-E Soil Moisture Data to Study Extent of March 2004 Flood
In early March 2004, a fast-moving line of thunderstorms stretched about 300 miles from central Kansas to northern Texas, dumping nearly two inches of rain in southern Kansas in one day and more than three inches in parts of central Oklahoma. Tornado and flood watches were issued for dozens of counties. The following maps from the NOAA National Climatic Data Center show the severity of the storm.
Precipitation Map, 29 February - 06 March 2004. Larger image.
NEXRAD Reflectivity Image, 03 March 2004. Larger image.
Developing Thunderstorm. Image courtesy of NOAA Severe Storms Laboratory.
Fortunately, improved spaceborne technologies are available to help scientists study the extent of excessive soil moisture following a severe storm. The Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) sensor aboard NASA's Aqua satellite, launched in May 2002, provides the first opportunity to obtain quantitative soil moisture data for global hydrologic and climate studies. Previous microwave radiometers did not provide high enough spatial resolution or optimal frequency range to monitor changes in soil moisture.
Steven Chan of the Terrestrial Science Research Element division of NASA's Jet Propulsion Laboratory analyzed AMSR-E soil moisture data for the midwestern U.S. immediately following the March 2004 storm. The first image below shows the spatial extent of retrieved soil moisture stretching across Kansas, Oklahoma, and Texas on 06 March 2004, which correlates well with the flood extent. This date was selected based on the observed maximum spread of retrieved soil moisture during the observation period. Soil moisture values less than 20 percent by volume are not shown in the image.
Following are time-series snapshots of retrieved soil moisture from 03 to 11 March 2004. They show a gradual buildup and reduction of soil wetness as the storm raged through the region.
Another view of soil moisture extent is shown below in four discrete intervals (20-23%, 23-26%, 26-29%, and 29-32%), along with the temporal variation of the coverage area, which Chan calculated by multiplying the number of EASE-Grid cells within the contoured region by 25 km2.
Brown, Angela. "Strong thunderstorms roll through east Texas, Oklahoma." Anchorage Daily News. 04 March 2004.
http://www.adn.com. Accessed 16 April 2004.
"Wind Storms Hit Texas, Oklahoma." CBSNews.com. 05 March 2004.
http://www.cbsnews.com/stories/2004/03/05/national/main604199.shtml Accessed 16 April 2004.