The catastrophic mudslides

Around midnight on Aug. 8, 2010, a violent surge of loosened earth roared down mountain slopes and slammed into quietly sleeping neighborhoods in Zhouqu County in Gansu, China. The catastrophic mudslides -- the deadliest in decades according to state media -- buried some areas under as much as 23 feet (7 meters) of suffocating sludge. 1,765 people died. Property damages totaled an estimated $759 million. Cutting from right to left, this detailed image, from DigitalGlobe’s WorldView-2 satellite, shows the largest slide in the lower part of the city on Aug. 10, 2010.
Credit: Image from WorldView-2 © 2010 by DigitalGlobe

A NASA study using TRMM satellite data revealed that the year 2010 was a particularly bad year for landslides around the world.

A recent NASA study published in the October issue of the Journal of Hydrometeorology compared satellite rain data from NASA’s Tropical Rainfall Measurement Mission (TRMM) to landslides in central eastern China, Central America and the Himalayan Arc, three regions with diverse climates and topography where rainfall-triggered landslides are frequent and destructive hazards to the local populations.

The work, led by Dalia Kirschbaum, a research physical scientist in the Hydrological Sciences Laboratory at NASA's Goddard Space Flight Center in Greenbelt, Md., is part of an ongoing effort to catalog worldwide rainfall-triggered landslides—one of the world's lesser known but often catastrophic natural hazards. Locating them is a step in an effort to be able, one day, to predict and warn.

Currently, Kirschbaum explains, no consistent regional or global scale warning system exists for landslide disasters. To create one, scientists need to understand more than the individual factors that may contribute to local landslides -- the intensity and total amount of rainfall over hours to days, slope angle, soil type and saturation, among others.

"For other hazards like hurricanes, there's a clearly defined season," says Kirschbaum. "From satellite data and observations we know that hurricane season in the Atlantic spans from June 1 to Nov. 30. But we don't have that type of record for landslides around the world, and we want to know when and where to expect them in different regions."

Scientists also need a systematic way to assess landslide hazards for a region, and one way to do that, says Kirschbaum, is to look at the distribution and intensity of rain from satellite data and see how that correlates with where and how often landslides are being reported.