El Niño happens when the sea water temperature rises in surface waters of the tropical Pacific Ocean. Every two to five years the Pacific Ocean has this event. A weak, warm current starts around Christmas along the coast of Ecuador and Peru. It lasts for only a few weeks to a month or more. Every three to seven years, an El Niño event may last for many months. This can change the weather and have important effects around the world. Australia and Southeast Asia can have drought but the deserts of Peru have very heavy rainfall. East Africa can have both. In a La Niña event the weather patterns are reversed.