Extreme Rain and Flooding in Australia Drops Global Sea Levels

Rain in Australia may be having some unanticipated side effects. While floods have swept across the landscape, it seems that the oceans are also being affected. It turns out that rising waters on land means lowering global sea level rise.

In 2010 to 2011, three atmospheric patterns came together over the Indian and Pacific oceans. These patterns drove vast amounts of rain over Australia, drenching the continent. In fact, so much rain fell that the world's ocean levels dropped measurably. Unlike other locations, the soil and topography of Australia prevent almost all of its precipitation from running into the ocean. This means that any rain that falls is kept on the continent rather than contributing to sea level rise.

In fact, scientists found that for an 18-month period beginning in 2010, the oceans dropped about .3 inches. That more than offsets the annual sea level rise of about .1 inches annually. After a bit of researching, the scientists discovered that this drop coincided with the atmospheric oscillation known as La Niña, which cooled tropical surface waters in the eastern Pacific and enhanced rainfall patterns over portions of the tropical Pacific, Africa, South America and Australia.

Yet the picture was a bit more complex than simply blaming the rainfall on La Niña. The researchers used a combination of satellite instruments and other tools to further examine the climate in 2010. They found that a rare combination of two other semi-cyclic climate modes came together to drive large amounts of rain over Australia--so much that the continent received almost a foot more rain than average.

"No other continent has this combination of atmospheric set-up and topography," said John Fasullo, the lead author of the new study, in a news release. "Only in Australia could the atmosphere carry such heavy tropical rains to such a large area, only to have those rains fail to make their way to the ocean."

What is more interesting, though, is the fact that there is now a reversal of this trend. Since 2011, when the atmospheric patterns shifted out of their unusual combination, sea levels have been rising at a faster pace of about .4 inches per year. This could be due to increased melting, but also shows that the ocean seems to be "making up" for lost time.

"It's a beautiful illustration of how complicated our climate system is," said Fasullo. "The smallest continent in the world can affect sea level worldwide. Its influence is so strong that it can temporarily overcome the background trend of rising sea levels that we see with climate change."

The findings are published in the journal Geophysical Research Letters.