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Tropical cyclones packing more punch further from the equator

By Will Dunham

WASHINGTON (Reuters) - People in heavily populated Pacific and Indian Ocean coastal regions beyond the tropics should take heed, U.S. scientists said on Wednesday, because tropical cyclones increasingly are packing their biggest punch farther from the equator.

Over the past 30 years, the location where these powerful storms reach their maximum intensity has shifted away from the equator and toward the poles in both the northern and southern hemispheres at a rate of about 35 miles (56 km) per decade, they said. That amounts to half a degree of latitude per decade.

The trend may be linked to factors that have contributed to global climate change including human activities like the burning of fossils fuels, the researchers said.

The scientists documented the greatest migration in tropical cyclones in the northern and southern Pacific and south Indian Oceans. This march away from the equator was not seen in the Atlantic, although hurricanes have registered increases in average intensity due to factors that may be counteracting the poleward trend seen elsewhere, the researchers said.

The storms that menace coastal regions with damaging winds and flooding are known as hurricanes in the Atlantic and eastern Pacific, typhoons in the western Pacific and tropical cyclones in the Indian Ocean and Southern Hemisphere.

The movement of maximum intensity means regions further north and south of the equator that have not dealt with many of these storms may now be in the crosshairs.

"We found that the tropics are becoming less hospitable to tropical cyclones and the higher latitudes are becoming less hostile," said Jim Kossin, an atmospheric research scientist with the National Climatic Data Center of the U.S. government's National Oceanic and Atmospheric Administration (NOAA) who led the study appearing in the journal Nature.

"So places in Japan and South Korea could find themselves at greater risk," Kossin said in a telephone interview. "Places in the southern Philippines might experience reduced risk."

As these storms creep into higher latitudes, some regions closer to the equator may experience reduced risk of being battered by them, the researchers said. On the other hand, these regions in the tropics that rely on rainfall spawned by these storms for fresh water resources may experience water shortages as the storms migrate away from them, they added.

Gabriel Vecchi, an atmospheric scientist at NOAA's Geophysical Fluid Dynamics Laboratory, said the researchers could not say with certainty whether increases in greenhouse gases or stratospheric ozone depletion have caused the poleward movement. But Vecchi said the latitude of maximum intensity has moved toward the poles at roughly the same rate as an expansion of the Earth's tropics over the same period, and other studies have attributed the tropics' expansion to human activities.

The scientists tracked the trend using satellite and other data spanning from 1982 to 2012 collected by NOAA's National Climatic Data Center. While the study documented the trend over a period of three decades using the data, it may very well have begun well before, Kossin said.

(Reporting by Will Dunham; Editing by Tom Brown)

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