Apr 3, 2017

Meteorology of Saturday's Colombian Flood Disaster That Killed 254

Mocoa, Putumayo
Colombia
by
Jeff Masters and Lee Grenci
,
Category 6
Mocao, Colombia after the Saturday, April 1, 2017 flood.  A video from early Saturday morning showed cars and trucks being swept down the streets. Photo:  Ejército Nacional de Colombia via Facebook
Mocao, Colombia after the Saturday, April 1, 2017 flood. A video from early Saturday morning showed cars and trucks being swept down the streets. Photo: Ejército Nacional de Colombia via Facebook

At least 254 people were killed in the in the city of Mocoa (population 40,000) in southwest Colombia near the border of Ecuador early Saturday, when torrential rains triggered a debris flow on a nearby mountain that surged into the town as a huge wall of water carrying tons of mud and debris. The disaster is the fourth deadliest weather-related disaster in Colombia’s recorded history. Reports from Colombia indicate that 130 mm (5.1”) of rain fell during a short period on Friday night and early Saturday morning, with the heaviest of the rain falling in just two hours, between 23:00 Friday, 31 March and 01:00 Saturday, 01 April, 2017. The rains fell on soils that were already wet from unusually heavy rains during March; the Mocoa region received about 50 percent more precipitation than usual during the month of March. The heavy rains of Saturday morning triggered a debris flow down the Taruca ravine on the northwest side of Mocoa, and this landslide, accompanied by floodwaters, poured into the Sangoyaco River and rampaged through the city of Mocoa. According to a USA Today interview with Jonathan Godt, coordinator of the U.S. Geological Survey’s landslide hazards program, “That mixture can move at 35-40 miles an hour, and because it’s so dense it has a lot more momentum and destructive power than water alone.”

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 President Juan Manuel Santos blamed climate change for triggering the flood, and he has a point—increased evaporation from warming oceans have caused a significant rise in atmospheric water vapor and very heavy rainfall events like the Mocoa event in recent decades. The Mocoa rains were triggered by a very moist flow of air from the tropical Atlantic, where ocean temperatures were near average. The rainy season in Colombia extends from March to mid June, so additional floods and landslides can be expected the next two months.