The El Nino Southern Oscillation (ENSO) is a cycle of warm and cold temperatures of the tropical central and eastern Pacific Ocean. The warm phase of ENSO is called "El Nino," while the cool phase is referred to as "La Nina."
The El Nino phenomenon occurs at irregular intervals, every two to seven years. It causes increased rainfall across east-central and eastern Pacific Ocean, including the South American west coast. Depending on its strength, El Nino can lead to major flooding.