The long-term average is about ten storms a year, with about one and a half developing into "major" hurricanes, Landsea noted. "That number is likely to increase to three per year in the next several decades," he added.
Tropical cyclones undergo a series of phases—from tropical depression to tropical storm—before being defined as a hurricane.
Once a storm is designated a hurricane, it is measured on a scale from one to five based on wind speed (the Saffir-Simpson Scale). Storms designated as Category 3 and above are considered major hurricanes. A Category 3 storm has wind speeds of 110 to 130 miles per hour.
The new findings apply only to the Atlantic Ocean, the Caribbean, and Gulf of Mexico. Accurate records of hurricane activity date back 60 years for the Atlantic Ocean and the western Northern Pacific Ocean, but only about 30 years elsewhere. The lack of reliable records makes it impossible to identify long-term trends in other regions of the world.
Planning Ahead
The researchers warn that the long period of generally low hurricane activity from 1971 to 1994 may have lulled us into a false sense of security.
"We're looking at up to a five-times increase in damage costs from hurricanes," said Landsea. "Over the last 30 years we've been fortunate, with annual costs to the continental U.S. at about $500 million. That's likely to increase to about $2.5 billion."
The toll is much higher in other affected regions. In the Philippines, about 5 percent of the gross national product is spent on hurricane recovery. More than 10,000 people died in Honduras and Nicaragua when Hurricane Mitch struck in 1998.
The loss of human lives and damage to property can be expected to rise in the years ahead because of population growth, increased affluence, and greater development of infrastructure in many coastal regions over the last 40 years.
The extended period of generally reduced hurricane activity in recent years may have lulled hurricane-prone regions into a false sense of security, Landsea suggested. He said governments may need to rethink their emergency plans to determine whether they would be adequate if hurricanes in the next several decades become as severe as those of 1920 to 1960.
Co-authors of the scientific report were Stan Goldenberg, a meteorologist at the U.S. National Oceanic and Atmospheric Administration, Alberto Mestas-Nuñez of the University of Miami, and William Gray of Colorado State University.
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