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World: Global Weather Is Hard To Predict

  • Charles Recknagel

From droughts in the Middle East to floods in Mozambique, natural disasters this year have proved once again how hard it is to predict the weather. But as RFE/RL correspondent Charles Recknagel reports, scientists are beginning to understand the world's climate and may be better able to foresee future patterns.

Prague, 24 May 2000 (RFE/RL) -- If people in the Middle East and southern Asia suspect there is a relationship between the droughts they have been suffering and the excessive flooding in Mozambique earlier this year, they are right.

The two weather extremes are part of a disruption in the climate of the Indian Ocean region in which winter rainfall patterns this year shifted on a large scale. Instead of the rainfall being dispersed across the region, it migrated southward, causing a pair of natural disasters that are two sides of the same coin.

Scientists say they are still far from fully understanding why such shifts in regional rainfall take place, and farther still from reliably predicting them in advance. But over the past decades, research has begun to suggest some precursor signs to look for which may one day provide a means of anticipating droughts and floods before they occur.

One of the most promising avenues of research is study of the much-talked about "El Nino-La Nina" phenomenon in the Pacific Ocean. It is a natural cycle in which the vast ocean's surface temperature first warms in a phase dubbed El Nino, then cools in a phase known as La Nina, as colder water wells up from the ocean depths.

The cycle, which has been going on since the ocean took shape, usually takes about one year to swing from the warming phase to the cooling. And it appears the cycle may be a motor for many of the planet's weather changes, because the heat the ocean adds and subtracts from the atmosphere can create dramatic shifts in wind and rain patterns over great distances.

Mike Davey, a climatologist at the British government's Meteorological Office in south-central England, told RFE/RL that both the flooding and the droughts in the Indian Ocean region this year appear to be associated with the El Nino-La Nina cycle.

"[The floods in Mozambique] and the conditions in the greater Horn of Africa are mostly due to the year-to-year climate swings which occur and these appear to be associated with this time the El Nino-La Nina cycle that's going on in the Pacific Ocean region, in particular."

He continues:

"The changes in the ocean and atmosphere interaction mean that the rainfall patterns and wind patterns shift on a large scale even as far away as Africa and beyond. And it is really those shifts which are to some degree predictable, that are bringing the current dry conditions which we are seeing in the greater Horn [of Africa] region and also associated with those [flood] weather conditions which we saw further south in Africa. These climate shifts that occur really are shifts, in that the rainfall tends to move from one place to another, so that what one place loses, another region gains."

Climatologists say this means that if the El Nino-La Nina cycle in the Pacific Ocean is better understood, the information could help build models of what will happen around the globe in response to the degree to which the great ocean alternately warms and cools. But that process is complicated by the fact that other variables, including a range of atmospheric conditions -- also influence regional weather. That makes building a predictive model a very complex task.

And even as some factors become better understood, new variables emerge. One is the phenomenon of global warming -- which some scientists have suggested will bring more frequent and intense droughts to some areas just as it brings coastal flooding from the melting of the polar caps to others.

Davey says that is still too early to know what influence on droughts and floods global warming ultimately may have. But he says we could see some early effects within the next few decades as global warming begins to influence the El Nino-La Nina cycle. Davey:

"We have a rather weak global warming at present, and superimposed on that we have this robust El Nino cycle, and other cycles as well, influencing the climate shifts. Now, what happens if we look 50 years ahead when global warming really starts taking a firm hold, and what effect that will have on El Nino, is really an important question. Because one of the important consequences of global warming may indeed be changes in the strong climate anomalies which are associated with the El-Nino cycle."

Davey adds:

"There is evidence that there might be some changes in perhaps the frequency or intensity of these El Nino events, as global warming takes off and the two phenomena start interacting with each another."

In the meantime, scientists around the globe continue to collect ever more data on how the climates in very different regions of the world seem to be interconnected. And they say they are confident that one day they will be able to spot trends -- both on a local and global level -- which can predict a coming natural disaster before it happens.

That, of course, will do nothing to prevent the next drought or flood from occurring. But it could at least help people make preparations weeks or months in advance, so that future crises will be less difficult than they are today.