How does El Nino cause drought?

Answer 1

El Niño is a weather phenomena which tends to occur in tropical waters of the Pacific Ocean. It affects the region across the Pacific from New Guinea to South America. During an El Niño season, which occurs on average every 2-7 years, a shift in ocean currents and winds brings warm water in a westerly direction, displacing the usual cold water that comes up from the ocean depths. As well as affecting marine life, the El Niño has an effect on weather patterns. Under normal conditions, in the tropics warm oceans tend to be accompanied by heavy rains, resulting in heavy rains in the warm west Pacific while the cooler east Pacific receives far less rainfall. This is reversed during an El Niño, when the ocean temperature gradient from one side of the Pacific to the other weakens. Warmer than usual ocean temperatures cause droughts in the west, while the unusually warm eastern waters bring heavy rains and floods to the Pacific coast of South America, which is usually much drier. It's all a matter of interactions between the oceans and the atmosphere. Changes in sea surface temperatures causes a shift in air pressure which, in turn, can result in climatic anomalies, such as severe droughts, flooding and even cyclones. One of the effects is that the normal circulation patterns over the Pacific are disrupted, and moisture-bearing trade winds weaken, whilst drier westerlies increase.