Rainy Days Ahead

The planet's water cycle has gotten more intense

Global warming has caused more rain to get dumped on rainy parts of the world and dry regions to dry up even more, according to a Science study. While climate change models had already predicted these trends, the new research suggests the changes are happening about twice as fast as expected.

Climate models have forecasted that the water cycle, or patterns of precipitation and evaporation, will become more intense as the planet warms. But confirming that this trend is occurring has been difficult. Scientists have little long-term data showing how much rain has fallen over the oceans, which gets most of the Earth’s rain, and satellites have been gathering this information for only about 15 to 30 years.

The study authors took a different tack. They studied the salinity, or saltiness, of the oceans, which fluctuates depending on rainfall and evaporation. Areas with more evaporation have saltier waters, while rainy areas have fresher waters.

After examining salinity records from 1950 to 2000, the team concluded that salty parts of the ocean “are getting saltier, whereas fresh regions are getting fresher.” These results suggest that the globe’s water cycle has indeed intensified over the last half-century. And the rate of intensification was about twice as high as predicted by climate models. Such rapid changes in the water cycle are even more cause for concern than warming, the authors say. — Roberta Kwok | 26 April 2012

Source: Durack, P.J., S.E. Wijffels, and R.J. Matear. 2012. Ocean salinities reveal strong global water cycle intensification during 1950 to 2000. Science doi: 10.1126/science.1212222.

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