Tropical cyclones' role in ending drought in Southeast US charted

"Drought is a far more protracted natural disaster than a tropical cyclone, and drought can have a huge economic impact," said Dr. Peter Soulé, a professor in the Department of Geography and Planning at Appalachian State University.

"Generally, the news coverage of tropical storms runs to the negative, such as damages and lives lost," Soulé said. "However, there are some benefits to landfalling tropical systems from the rainfall they produce that can end drought conditions."

Storms that are considered tropical cyclones include tropical disturbances, tropical depressions, tropical storms and hurricanes. The beneficial effects of "drought busters" have been studied since 1968 when A. L. Sugg published "Beneficial Aspects of the Tropical Cyclone," in the Journal of Applied Meteorology.

Soulé and three other researchers analyzed tropical cyclones' role in reducing drought conditions in the Southeastern United States. Their work, "Drought-Busting Tropical Cyclones in the Southeastern United States: 1950-2008" was published in the March 2012 issue of the journal Annals of the Association of American Geographers.

Dr. Justin Maxwell from Indiana University was the lead author of the research article. In addition to Soulé, the other authors were Dr. Paul Knapp from UNC Greensboro and Dr. Jason Ortegren from the University of West Florida. 

They found that during the 58-year period, up to 41 percent of all droughts and at least 20 percent of droughts in three-fourths of the climate divisions in the Southeast were ended by tropical cyclone drought busters. In addition, they found that 4 to 10 percent of all rainfall in the Southeast occurred during the tropical cyclone season and that as much as 15 percent of rainfall in the Carolinas occurred from tropical cyclones.

"It turns out tropical cyclones were a very important process for ending drought," Soulé said of the time period and region studied.

"Drought can be a far worse natural hazard in terms of cost because it is so long lived and affects such large areas," Soulé said. "In the broad scheme of natural hazards it tends to rank high in terms of cost. People don't usually think about how bad drought can be and how much money drought can cost."

For example, the 1988 drought is estimated to have caused between $80 and $120 billion in damage including crop losses and destructive wildfires. Last year's drought across the Southeast cost more than $10 billion in agricultural losses. Droughts also impact urban and rural water quality.

Currently, 65 percent of the U.S. is experiencing drought, according to the drought monitor website at the University of Nebraska-Lincoln (http://droughtmonitor.unl.edu/). And while Tropical Storm Debby ended Florida's drought, there is no guarantee that any of the five hurricanes and 13 named storms predicted for this hurricane season will make landfall and bring relief to the Southeast.

Last year's season saw only one storm to make landfall in the Southeast.

"This year has been unusual in that we have already had four named storms, two which developed in May before the official beginning of the hurricane season on June 1," Soulé said. "But there is no way to know what this season is going to hold."