Vietnam flood relief aided by Dartmouth team

Posted 10/13/00

The United Nations World Food Program is using maps produced by Dartmouth's Flood Observatory to help target emergency food supplies to victims of current flooding in Southeast Asia.

Flooding along the Mekong River, estimated to be the worst in the area since 1961, has displaced hundreds of thousands of people in recent weeks. Using satellite imagery provided by NASA's Moderate-Resolution Imaging Spectroradiometer (MODIS) aboard the Terra spacecraft, Dartmouth Professor of Geography Robert Brakenridge and his colleagues have been able to produce detailed maps that provide information about the severity and precise location of flooding in the region.

"The MODIS maps are proving really useful to us," said Mahadevan Ramachandran, the United Nations World Food Program regional vulnerability analysis and mapping officer in Phnom Penh, Cambodia. "In areas like Cambodia and Laos where there are weak data collection systems on the ground, the MODIS data will be our first-hand information to identify the areas we need to visit and assess for ourselves."

Before the early 1990s, mapping of flooded lands was limited to occasional aerial photography surveys of specific floods. Brakenridge and colleagues used images from a spaceborne radar on the European ERS-1 satellite to produce some of the first satellite flood maps in 1993 of the extensive flooding in the upper Mississippi River valley that year.

Brakenridge began work on a global flood monitoring system in 1996 that would convert available satellite imagery into precise geographic information on flooded areas that could be distributed to disaster relief agencies through the World Wide Web. The result was the Dartmouth Flood Observatory.

"The Observatory is the first system for global flood monitoring using remote sensing," says Brakenridge. "We can use almost any data source and incorporate it into a global data base of flood-prone areas."

The Dartmouth Flood Observatory was developed with funding from NASA's Earth Observing System (EOS) program, which is managed at Goddard Space Flight Center. EOS is a program of multiple spacecraft missions and interdisciplinary science investigations to understand global climate change. Flood maps from the Dartmouth system have been used to aid relief efforts in Honduras after Hurricane Mitch in 1998 and in the Carolinas after Hurricane Floyd in 1999.

"MODIS has made an enormous difference in our flood mapping," says Brakenridge. "MODIS can image most of the world every day and it views a very wide area." The images are much more detailed than other readily available wide-area images.

The frequent heavy cloud cover over Southeast Asia makes it difficult to regularly see the surface and flooded areas, says Brakenridge. To overcome this problem, eight MODIS images from consecutive days are blended together to produce one image that combines all the cloud-free views of the surface. This new image product provides a look at how much floods rise or fall nearly every week.

Observations of floods in a region over successive years help disaster relief agencies like the United Nations unequivocally identify the largest flood events and allocate limited aid resources accordingly.

Ramachandran compares the new MODIS maps with 1999 flood maps to pinpoint hardest hit by the current flooding. "We overlay the MODIS maps with maps of crop production, poverty level, and land cover and land use derived from Landsat images to design our food aid relief efforts." The World Food Program is planning to feed nearly 500,000 people in Cambodia starting this month and continue aid for up to six months.

The growing Dartmouth Flood Observatory record of major floods around the world has another practical use: identifying flood-prone areas for national flood hazard reduction programs. The flood record is also being used to grapple with a tough scientific question: Are "great floods" around the world getting larger as the Earth's climate warms?

"We have to know how big a flood event is and keep a global record of such events in order to determine if climate change is accompanied by changes in the frequency and magnitude of big floods," says Brakenridge. NASA's EOS program recently funded a multi-year research proposal by Brakenridge on this question.

Click here for more information on the Dartmouth Flood Observatory.