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As the globe continues to warm, the rainiest parts of the world are very likely to get wetter, according to a new study in Science. Desert dwellers, however, are likely to see what little rain they receive dry up, as the rain becomes even more concentrated in high-precipitation areas.
Atmospheric scientists Richard Allan of the University of Reading in England and Brian Soden of the University of Miami looked at satellite records of daily rainfall stretching back to 1987 to see how warmer temperatures had affected precipitation. That's one of the key climate changes expected from rising greenhouse gas levels in the atmosphere. The researchers specifically focused on El Niño, the warming of the waters of the tropical Pacific that raises air pressure, changes winds, and recurs every few years.
The weather pattern causes floods in some areas and droughts in others while changing climate across the globe over time—and thus is a pretty good stand-in for global warming.
"For the period we examined, 1987 to 2004, there was a clear relationship between warm El Niño events and increased occurrence of heavy precipitation," Soden says. Such "events will certainly become more frequent in a warmer climate."
For example, other research has shown that monsoon storms that dump six inches (150 millimeters) or more of rain on India have become more common since the 1950s.
The satellite observations agree with the predictions of various computer models. The U.N. Intergovernmental Panel on Climate Change expects that such changes will wreak havoc on agriculture, human health and the natural environment.
But the Science study also reveals that the computer projections may be underestimating how severe such downpours may become. Warmer seas resulted in three times as many heavy rainstorms as the models would have predicted—and other studies have shown that such models fail to account for the rapid increase in water vapor in the atmosphere.
"It is very likely that heavy rainfall will become more common and more intense in a warming world," Allan says. "It is too early to say by how much real world changes in rainfall will surpass projections from the climate models."