The ‘girl’ who unleashed the torrential rains

2011-01-22 17:03

The “girl” who has wreaked havoc in the southern hemisphere will be with us until at least March.

Called “La Niña” (Spanish for “the girl”), she appeared in the middle of last year, causing severe wet weather which, in the New Year, caused:

» The worst flooding in 35 years in Australia. The death toll is at 22 and more flooding is expected;

» Flash floods and mudslides in Rio de Janeiro, killing more than 740 people – one of Brazil’s worst recorded natural disasters;

» Flooding in the Philippines which killed 57 people;

» Flooding in Sri Lanka, which is still recovering from a tsunami that struck in 2004. Forty-three people were killed and more than one million affected by the heavy rains; and

» Flooding, lightning and storms in South Africa that have claimed the lives of 70 people, displaced more than 8 400 around the country and destroyed infra- structure worth hundreds of millions of rands.

The South African Weather Service (SAWS) predicts a very good chance of above-normal rainfall over much of the country until April.

“Further heavy rain and flooding are possible in parts of South Africa, but it is too early to say where this might occur,” says Mnikeli Ndabambi, the senior manager for forecasting at the SAWS.

He explains La Niña as a phase of the El Niño/Southern Oscillation which began in the middle of 2010 (see sidebar).

During El Niño there is abnormally wet weather in dry climates and dry weather in typically wet regions.

During La Niña, however, there is abnormally drier weather in dry climates and wetter weather in typically wet locations.
A La Niña event occurs every three to four years.

“La Niña affects the weather of the continents surrounding the Pacific Ocean. Through a ‘knock-on’ effect, the weather in more distant places like South Africa can also be influenced,” Ndabambi says.

He adds that the link between La Niña and heavy rainfall in South Africa is not direct because the Atlantic and Indian Oceans also play an important role in SA’s weather conditions.

“On average, however, we tend to receive above-normal summer rainfall during La Niña.”

In future severe weather events are expected to increase in their frequency and their intensity, says Ndabambi.

The current severe weather experience worldwide could be the result of a mixture of the La Niña phase and climate change, says Dr Mark Tadross from the Climate Systems Analysis Group at University of Cape Town: “But no one really knows how much climate change is contributing to the severe weather.”

While scientists are not able to pinpoint whether severe weather events are a direct result of climate change, they can make predictions about the impact that climate change may have on weather patterns in the future.

“We do expect that by 2050 the eastern parts of the country will experience increases in average rainfall,” says Tadross.


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