WASHINGTON -- The nation's coastal population has exploded in recent years during a period of fewer than normal hurricanes, meaning millions could be in harm's way should the number of storms rebound.
Researchers at Florida State University point to a downward trend in hurricanes striking coastal sections of the Gulf of Mexico.
The peak period was 1916-1925 when 14 of the storms came ashore, including six severe hurricanes, they reported in the July edition of the Bulletin of the American Meteorological Society.
By contrast, nine hurricanes, including four severe ones, made landfall in 1976-85 and eight, one severe, occurred in 1986-95.
The research was prompted by New Orleans officials' concerns that global warming would lead to more hurricanes striking that city, located on the Gulf and largely below sea level.
"So we sat down and looked at the available data, and saw there's really no trend yet to support that" fear, said Mark C. Bove, a graduate assistant at Florida State's Center for Ocean-Atmospheric Prediction Studies.
However, the sharp growth of coastal communities -- with populations now totaling an estimated 47 million -- has placed more people at risk when storms do occur, Bove said, echoing a threat emergency preparedness managers have been citing for years. Most of those people have never been through a major hurricane, and emergency planners fear new residents may not respond to warnings when a storm does occur.
While saying it's hard to pinpoint a reason for the decline in recent decades, Bove said in a telephone interview that the El Nino phenomenon and other climate variables can affect hurricane frequency.
El Nino, an unusual warming of water in the eastern Pacific Ocean, can change weather worldwide and scientists say that years when it occurs tend to have few hurricanes in the Atlantic Ocean and Gulf of Mexico.
Last summer was marked by a strong El Nino, and just one hurricane made landfall in the United States, for example. Now that El Nino has ended, disaster preparedness officials fear more storms this summer.
William Gray, a hurricane expert at Colorado State University, has found indications of a 30-year cycle in hurricanes, Bove said.
Many scientists are also concerned about the so-called greenhouse effect, which could lead to warmer temperatures worldwide as carbon dioxide and other chemicals are added to the atmosphere. Various studies have suggested this warming could cause droughts, floods, heat waves, hurricanes and even spread disease.
Bove said that he, graduate student David F. Zierden and professor James J. O'Brien studied hurricanes back to 1896 because those were the most reliable records available. A further analysis of the relationship between Atlantic hurricanes and El Nino is expected to be published in the fall, he said.
Their report on Gulf hurricanes focuses on storms that came ashore between Cape Sable, Fla., and Brownsville, Texas. To be rated as a hurricane, a storm must have sustained winds of at least 65 knots (74.7 mph). To be considered severe, it must have winds of 96 knots (110.4 mph).
Here's the study's rundown on the hurricanes coming ashore along the Gulf Coast per decade:
-- 1896-1905: 8 storms, 1 severe.
-- 1906-1915: 13 storms, 6 severe.
-- 1916-1925: 14 storms, 6 severe.
-- 1926-1935: 11 storms, 7 severe.
-- 1935-1945: 13 storms, 4 severe.
-- 1946-1955: 9 storms, 3 severe.
-- 1956-1965: 10 storms, 5 severe.
-- 1966-1975: 11 storms, 5 severe.
-- 1976-1985: 9 storms, 4 severe.
-- 1986-1995: 8 storms, 1 severe.