El-Nino and Peru's floods

Peru's Floods Follow Climate Change's Deadly Extreme Weather Trend

An unusual coastal El Niño drove Peru's deluge, in another signal that weather extremes are becoming wild cards as climate change warms the oceans.

Inside Climate Change,

6 April, 2017

Peru's worst floods in nearly a century have killed more than 70 people, left 70,000 homeless in nearly every province and damaged 130,000 structures, including ancient archaeological sites. The downpours inundated the country in the first half of March, then moved north over Colombia, causing a mudslide that killed hundreds.

The intense rain and flooding in Peru took emergency workers and scientists by surprise, because such extreme downpours typically are associated with a large-scale El Niño phenomenon. But the latest El Niño ended nearly a year ago.

The flooding instead has been linked to an exceptional and sudden emergence of extra-warm ocean waters just off Peru's coast, what scientists call a coastal El Niño. Since mid-March, NOAA satellites have showed this patch of the eastern Pacific as the most anomalously warm ocean region in the world. 

It won't be clear whether human-caused global warming was a direct factor in the flooding unless scientists do an attribution study. That would determine how much the buildup of heat-trapping greenhouse gases increased the odds of it happening.

But the unusual flooding is consistent with the extreme weather expected as climate change warms the oceans, according to scientists.

"There's been a big increase in really heavy rainfalls around the world. Storms are moving more slowly, carrying more moisture. That's the new normal," Jim White, said director of the Institute of Arctic and Alpine Research at the University of Colorado, Boulder.

"At 400 ppm of CO2 in the atmosphere, pretty much everything should be carrying a signature of climate change, it would be odd if it didn't. The question is not so much is this event caused by climate change. The question is, which event is not?"

Since the 1950s, the world's oceans have absorbed more than 90 percent of the extra heat trapped in the Earth's atmosphere as a result of the increase in greenhouse gas emissions.

"The eastern equatorial Pacific has warmed by about 0.5 to 1 degree Celsius since 1950, which is likely a result of anthropogenic climate change," said Mojib Latif, a climate scientist at the GEOMAR-Helmholtz Centre for Ocean Research in Kiel, Germany.

"This could be sufficient to boost the impacts of a coastal El Niño."

South America is not alone in experiencing coastal ocean heatwaves. Other recent examples include the notorious warm blob that persisted off the coast of the Pacific Northwest from 2013-15 that spawned a toxic algae bloom and shut fisheries. Persistently warm ocean temperatures off the eastern U.S. coast and in the Caribbean likely intensified tropical storms like Matthew and Irene, according to climate scientists, and record ocean warmth in the Gulf of Mexico helped fuel the devastating downpours and floods last August in Louisiana.

Local marine heatwaves like Peru's have been linked with stagnant weather patterns  and the increase in ocean heat content, which are both caused by global warming.

Overall ocean warming also helps intensify the local ocean heatwaves, according to climate researcher Kevin Trenberth from the National Center for Atmospheric Research. "Ocean dynamics play a role and can help sustain hot spots by replenishing them with more warm water from elsewhere."

Attribution studies that determine climate change's role in individual weather events, such as droughts, heatwaves and floods, can improve long-term forecasts. That can help relief agencies prepare, said Hannah Cloke, a University of Reading climate researcher and flood expert who works with the Red Cross/Red Crescent Climate Center. Her organization partners with Climate Central's World Weather Attribution Program, which has done several recent rapid attribution studies.

"If there is a link, you could provide better early warnings for floods like this. It's a matter of life and death for people that live there," she said.

If it's requested by the Peru government or the Red Cross climate organization, the WWA may study the possible link between global warming and the Peru rainstorms, said Geert Jan van Oldenborgh, a climate scientist with the Royal Netherlands Meteorological Institute, who recently led a similar study for the devastating floods in Louisiana.

His team's study of the Louisiana floods found that human-caused climate change increased the odds of the event by 40 percent, and boosted the rainfall totals by 10 percent. The Louisiana floods cost at least $15 billion.

U.S. government forecasters say there's a chance the warm water off the coast of Peru is the first sign that a new large-scale El Niño is developing, but for the people in Peru affected by the floods that hardly  matters. The bottom line is that record rains were fueled by unusually warm local water temperatures, boosted by long-term ocean-wide warming, according to Trenberth.

"For the poor people in Peru, this is a pretty dramatic climate change. It's the real deal. They don't have the infrastructure to deal with prolonged rains, and this is causing millions of dollars worth of damage," he said. "Scientists in North America may be scratching their heads and talking about whether we've got an El Niño or not, but in Peru, it's not theoretical at this point. In Peru it's real."