Scientists Link Warmer Temperatures to Rainfall Extremes

Heavy rain events increase during warm periods and decrease during cold periods, according to the scientists in Florida and England who said today that their research is the first to provide observational evidence linking higher temperatures with heavier rains.

"We use satellite observations and model simulations to examine the response of tropical precipitation events to naturally driven changes in surface temperature and atmospheric moisture content," they explained.

The study focused on changes in sea surface temperatures associated with El Niņo, a pattern of warming in the central tropical Pacific Ocean off the coast of South America that results in floods, droughts, and other disturbances around the world.

El Niņo patterns occur at irregular intervals of two to seven years and usually last from one or two years.

Based on satellite observations combined with data from computer models the scientists found "a distinct link" between tropical rainfall extremes and temperature.

"A warmer atmosphere contains larger amounts of moisture which boosts the intensity of heavy downpours," said study author Dr. Brian Soden, an associate professor of meteorology and physical oceanography at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.

A thunderstorm over Miami, Florida. August 5, 2008 (Photo by Don Shackleford)

This means that projections of future changes in rainfall extremes due to global warming caused by human activities may be underestimated, and future rains may be even heavier than previously thought.

"Comparing observations with results from computer models improves understanding of how rainfall responds to a warming world," said co-author Dr. Richard Allan of the University of Reading's Environmental Systems Science Centre.

"Differences can relate to deficiencies in the measurements, or the models used to predict future climatic change," he said.

Established by the UK's Natural Environment Research Council, ESSC undertakes research into how life, land, oceans, atmosphere and ice sheets interact with each other.

Soden says the sensitivity of the Earth's climate to an increase in the greenhouse gas carbon dioxide depends on the response of clouds and water vapor.

"My research strives to better understand the role of atmospheric hydrologic processes in governing climate and climate change through the use of satellite observations and mathematical models of Earth's climate," Soden says on his website. "This research is motivated by the need to better understand how human activities are altering Earth's climate."

The report, "Atmospheric Warming and the Amplification of Precipitation Extremes," is previewed online in "Science Express" today, and set for publication in an upcoming issue of the journal "Science," a publication of the American Association for the Advancement of Science.

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