资料LaNina.docx

Experts say the Pacific ocean phenomenon known as La Ni?a is partly to blame for the drought ravaging the Horn of Africa.But while the latest La Nina episode has ended, climate scientists are concerned about what the next few months will bring and the intensifying effects of a changing global climate.La Ni?a begins when eastern Pacific waters near the equator turn cooler than normal. A cascade of changes in ocean temperatures and wind currents follows, and the consequences are global.Droughts and floodsThe latest episode began in July of last year.In the United States, altered winds pushed moisture away from the south, causing severe droughts that persist today, and toward the north, causing floods.Half the world away, flooding in Australia this winter was also linked to La Ni?a, experts say.And in Africa, The easterly winds that are supposed to bring moisture into East Africa [were] reduced, says meteorologist WassilaThiaw, head of the Africa desk at the U.S. National Weather Services Climate Prediction Center. There was less moisture coming into East Africa and therefore rainfall is reduced.Rains that were supposed to fall over Somalia, southern Ethiopia and northern Kenya late last year failed.Lost rainy seasonThe second rainy season in that part of the Horn of Africa, from March through May, failed, too, but for different reasons, he says.What played out here during the March-April-May season, we dont think that is really La Ni?a, but it probably mostly due to the atmospheric conditions that prevailed at that time.He says La Ni?as influence on the March-through-May rainy season typically is not as strong as on the October-through-December season. Natural variations in atmospheric conditions were enough to prolong the drought, he says.Rainy season threatenedThis La Ni?a episode ended in May. But Thiaw says there is a chance another one may begin by the end of this year.If that happens before the October-through-December rainfall season, then theres a high chance