Predictions of floods in Mozambique were ignored

By Fred Pearce, New Scientist . 03.09.00

As Mozambique struggles to recover from its devastating floods, one person can claim to have predicted the heavy rains over the region that caused the disaster.

Mark Jury, a climate modeller at the University of Zululand in South Africa, warned in a press statement last September of a "wet, wet" start to 2000 in southern Africa. If more notice had been taken, he says, the floods could have been reduced.

In January, when international forecasters were cautiously predicting above-average rains, Jury said there would be 75 per cent more rainfall than usual in the catchment area of the River Limpopo, which has caused the bulk of the flooding in southern Mozambique. Remarkably, while the international experts used supercomputers running complex global climate models, Jury's model runs on a PC.

By analysing historical data on atmospheric and ocean conditions, it predicts the weather in southern Africa up to six months ahead. Jury will be discussing his forecasting methods at a conference at the University of Southampton this week.

Like other forecasters, Jury says that the root cause of the floods was La Niqa--a cold-water oscillation in the equatorial Pacific--which is now at full force. In 8 out of 10 years when La Niqa is active, says David Parker at Britain's Meteorological Office in Bracknell, it brings above-average rains to southeast Africa. But Jury says he understands why this year was exceptional. "Sometimes weather conditions over the Indian Ocean amplify the impact. And this was one of those years."

Normally, cyclones and other weather systems coming west across the Indian Ocean are diverted south, away from land, by a jet stream heading the other way. "But this year the jet stream was weak and the storms came right on through," says Jury. "Many models ignore this element."

Tim Palmer of the European Centre for Medium-Range Weather Forecasts in Reading says: "We predicted above-average rainfall but nothing exceptional." He and Jury agree that predicting weather is made harder by the lack of temperature data on the Indian Ocean. "We still rely on passing ships," says Palmer.

Jury says that if dam managers on the Limpopo had taken more notice of the warnings by him and others, the flooding could have been reduced. "They have been keeping their reservoirs too full," he says. Managers contributed to the floods by emptying their dams in a panic as the rivers filled. "They should have started to empty them much earlier," Jury says

This view was echoed by Bryan Davies of the University of Cape Town, who wrote to his government last week warning that inappropriate management of dams on the River Zambezi could flood huge areas of northern Mozambique, leading to "tens of thousands" of deaths. Portuguese engineers in charge of the Cahora Bassa dam in Mozambique had abandoned the safety practice of partially emptying the reservoir behind the dam before the onset of the rainy season. Emergency discharges of water at Cahora Bassa were likely, he warned, resulting in "another flooding catastrophe".

-- cin (cinlooo@aol.com), March 12, 2000