Figure 1. Saturday’s opening of the first gate on the Morganza Spillway, as seen on the live feed from USTREAM.

Devastating flooding continues in Colombia
Devastating flooding has hit South America in Colombia, where exceptionally heavy spring rains have killed at least 425 people so far this year, with 482 others missing. Damages are in the billions, and there are 3 million disaster victims. “Some parts of the country have been set back 15 to 20 years”, said Plan’s Country Director in Colombia, Gabriela Bucher. “Over the past 10 months we have registered five or six times more rainfall than usual,” said the director of Colombia’s weather service, Ricardo Lozano. Up to 800 mm (about 32 inches) of rain has fallen along the Pacific coast of Colombia over the past two weeks (Figure 3). The severe spring flooding follows on the heels of the heaviest fall rains in Colombia’s History. Weather records go back 42 year in Colombia. Colombia’s president Juan Manuel Santos said, “the tragedy the country is going through has no precedents in our history.” The 2010 floods killed 571 people–the second deadliest year for floods in Colombian history, next to 1987. The floods did over $1 billion in damage, and affected 2.8 million people. In many places, the flood waters from this great disaster never fully receded, and are now rising again due to this latest round of intense flooding. More rain is in the forecast–the latest forecast from the GFS model calls for an additional 5 – 10 inches (200 – 400 mm) across much of western and northern Colombia in the coming week.

Figure 2. Satellite-observed rainfall over Colombia during the past two weeks shows a region of up to 800 mm (about 32 inches) has fallen near the Pacific coast. Image credit: Navy Research Lab, Monterey.

Colombia’s rainy season usually has two peaks: one the fall in October, then then another in the spring in April – May. The heavy rains are due to the presence of the Intertropical Convergence Zone, the area encircling the earth near the Equator where winds originating in the northern and southern hemispheres come together. When these great wind belts come together (or “converge”, thus the name “Convergence Zone”), the converging air is forced upwards, since it has nowhere else to go. The rising air fuels strong thunderstorm updrafts, creating a band of very heavy storms capable of causing heavy flooding rains. In La Niña years, when a large region of colder than average water is off the Pacific coast of Colombia, rainfall tends to increase over Colombia. La Niña was moderate to strong during the fall 2010 rains and floods in Colombia, and was largely to blame for Colombia’s deadly rainy season. However, in recent months, La Niña has waned. April sea surface temperatures off the Pacific coast of Colombia (0° – 10°N, 85° – 75°W), warmed to the 13th highest temperatures in the past 100 years, 0.68°C above average. Thus, this month’s flooding in Colombia may not be due to La Niña.

See also my December 2010 post, Heaviest rains in Colombia’s history trigger deadly landslide; 145 dead or missing

Figure 3. Dramatic video of flooding in Colombia over the weekend. Flood waters swept away cars and buses in a busy street in the city of Barranquilla, and passengers climbed on the roofs of their vehicles in order to escape the flood waters. Video credit: BBC.

300-year flood in Canada; wildfires destroy large portions of Slave Lake, Alberta
In Manitoba, Canada, heavy spring snow melt in combination with heavy rains have combined to create record flooding on the Assiniboine River. Authorities intentionally breached a levee over the weekend to save hundreds of homes, but inundated huge areas of farmland as a result. The flood is being called a 300-year flood, and damages are already in excess of $1 billion. In neighboring Alberta, the reverse extreme is causing havoc: severe drought and strong spring winds have made ideal conditions for wildfires, which swept into the community of Slave Lake (population 6,700) yesterday. The fires destroyed hundreds of buildings, burning down the town hall and at least 30% of the town, according to preliminary media reports.

Figure 4. Video of the May 15, 2011 Slave Lake fire.

First tropical wave of the year over the Atlantic
The first tropical wave of 2011 is now over the tropical Atlantic near 6°N 46°W, according to the latest Atlantic Tropical Weather Discussion. The wave will bring heavy rain to the northeast coast of South America over the next two days, but is too far south to be a threat to develop into a tropical depression. The Atlantic hurricane season is just two weeks away, and the Eastern Pacific hurricane season began yesterday. So far, the models are not predicting any tropical storm development in the East Pacific or Atlantic over the next six days.

Jeff Masters