Spike in extreme rains linked with global warming

Raindrops splashing into a pond in Vail. PHOTO BY DYLAN BERWYN.
A new study documents a distinct increase in extreme rainfall events linked with global warming.

Southeast Asia sees biggest increase in dangerous rainstorms

Staff Report

FRISCO —There’s clear evidence that global warming is causing more frequent record-breaking rainstorms, according to scientists with the Potsdam Institute for Climate Impact Research.

The upward trend in extreme rainfall events has been striking in the last 30 years, and particularly noticeable in Southeast Asia, the researchers said in a new study, explaining that the spike lies outside the range of natural variability.

The worldwide increase is consistent with rising global temperatures, which are caused by greenhouse-gas emissions from burning fossil fuels, the scientists said.

Extreme rainfall in Pakistan 2010 caused devastating flooding which killed hundreds and lead to a cholera outbreak. Other examples of record-breaking precipitation events in the period studied include rainstorms in Texas in the US, 2010, which caused dozens of flash-floods. And no less than three so-called ‘once-in-a-century’ flooding events in Germany all happened in just a couple of years, starting 1997.

“In all of these places, the amount of rain pouring down in one day broke local records … and while each of these individual events has been caused by a number of different factors, we find a clear overall upward trend for these unprecedented hazards,” lead author Jascha Lehmann said in a press release.

The average global increase in extreme precipitation is 12 percent, but soars to 56 percent in Southeast Asia, the researchers found in their statistical analysis of rainfall data between 1901 to 2010.

“Due to the upward trend, the worldwide increase of record-breaking daily rainfall events in the very last year of the studied period reaches … 26 percent,” Lehmann added.

The study also found geographic patterns, with wet areas getting wetter. The observed increase in record-breaking rainfall events reached 31 percent in Europe and 24 percent in the central U.S.

But record-breaking rain events declined in the western U.S. by 21 percent, and by 27 percent in the Mediterranean region.

The reason for the increase is simple. A warmer atmosphere can hold more moisture, which can be released during short-term heavy rainfall events.

“One out of ten record-breaking rainfall events observed globally in the past thirty years can only be explained if the long-term warming is taken into account,” said co-author Dim Coumou.

The researchers included the quality of historic weather data in their calculations. For example, rainfall measurements from the Sahara desert are scarce, which makes it harder to draw conclusions for the region.

Other areas, like Europe and the US, have detailed rainfall measurements going back many decades.

“The pronounced recent increase in record-breaking rainfall events is of course worrying,” Coumou said. “Yet since it is consistent with human-caused global warming, it can also be curbed if greenhouse gas emissions from fossil fuels are substantially reduced.”

Weblink to the article: http://dx.doi.org/10.1007/s10584-015-1434-y

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