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Rising global temperatures could be changing rainfall levels in the tropics, according to researchers.

Scientists at the Goddard Space Flight Center in the United States analysed the global rainfall record from 1979 to the present, logged by the Global Precipitation Climatology Project.

They found that while there has been no overall global change, rainfall over oceans in tropical latitudes increased by five per cent over the period and decreased by one per cent over land — a total increase of four per cent for the entire tropics.

The year 2005 saw the highest amount of rainfall on record over both tropical land and ocean. Two-thirds of all rain globally falls in the tropics.

The study was published this month (1 August) in the American Meteorological Society's Journal of Climate.

"Since we know there are long-term changes in temperature, the presumption is that these changes [in rainfall] are related to the temperature changes," Robert Adler, co-researcher on the study, told SciDev.Net.

He explained that the tropical oceans have experienced higher rainfall as higher temperatures create more moisture over oceans, resulting in more precipitation.

He added that people on the ground would probably not have noticed the rainfall changes, except for some subtle changes in the number or severity of storms.

Adler stressed that they do not know why rainfall is increasing specifically in the tropics, and said that more research is needed to establish a cause and effect relationship between change rainfall and the warming climate.

"What's interesting is that if this kind of change in precipitation is happening with temperature change, what's going to happen over the next 50 or 100 years?" says Adler.

If the changes continue, he says, there could be "significant problems for populations in these areas".

Adler said the next step is to verify the observations using new methods that use radar to detect rainfall, as part of NASA's Tropical Rainfall Measuring Mission.

Reference: Journal of Climate 20, 4033 (2007)

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