Study finds water cycle accelerating with warming

Wet gets wetter, dry gets drier

Climate models are inaccurate, but not in a comforting way: that’s the conclusion of an ocean salinity study conducted by CSIRO and the Lawrence Livermore National Laboratory, which indicates that changes in the water cycle are running faster than models predicted.

Based on the relationship between salinity, evaporation and rainfall, the scientists have concluded that the water cycle strengthened by four percent between 1950 and 2000 – which is double the rate predicted in current climate models.

The scientists, led by Dr Paul Durack at LLNL, also supports the idea that with a warming climate, wet regions are likely to get wetter, with a corresponding drying trend in already dry regions.

Durack says the study found “robust evidence of an intensified global water cycle at a rate of about eight percent per degree of surface warming”.

An enhancement of the water cycle, he said, is driven by the ability of warmer air to hold and redistribute more moisture.

The study, published in Science (abstract here), was designed to overcome the ambiguity of land-based observations of the water cycle. Salinity provides a good proxy for both rainfall and evaporation, and with a fleet of 3,500 profilers now in the field, the researchers are able to work with a global data set.

Moreover, as Durack points out, oceans receive 80 percent of the world’s rainfall, and have absorbed about 90 percent of the heat added to the Earth due to atmospheric warming.

While the error margin in Durack’s prediction is high (water cycle accelerating 8 percent plus-or-minus 5 percent per degree of atmospheric warming), even at the low end, he says, acceleration of the water cycle would have serious implications for freshwater availability. &reg

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