The great Mississippi River flood of 2011 continues to make history, with Saturday's opening of the flood gates of the Morganza Spillway marking just the second time that flood control structure has been used since its construction in 1956. With the Morganza, Bonnet Carre', and Birds Point-New Madrid Spillways all open, the Army Corps of Engineers has now opened all of its major spillways simultaneously for the first time ever. The Mississippi is rising at Vicksburg, Mississippi, where the water has now reached 56.5', exceeding the previous all-time record of 56.2', set during the great flood of 1927. Natchez, Mississippi, is also at its greatest flood height on record, with the water at 60.6'. The previous record high was 58', set in 1937. However, the opening of the Morganza spillway has reduced the predicted heights of the great flood of 2011 from Natchez to New Orleans by 1 to 1.5'. This will serve to greatly reduce the pressure on the levees and on the Old River Control Structure, which as
I discussed in my previous post, is America's Achilles' heel, and must be protected. According the
National Weather Service, flood heights along the Lower Mississippi from Natchez to New Orleans will peak this week, and slowly fall next week. Rainfall
over the next five days is expected to be minimal over the Lower Mississippi watershed. The next chance for significant rain over the region will come Sunday, May 22.
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 ColombiaDevastating 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