El Niño Southern Oscillation (ENSO)

The El Niño Southern Oscillation (ENSO) is a natural phenomenon which impacts the Pacific waters and results in changes to weather patterns all over the world. It also has significant impacts on the climate in Mexico.

There are three states which can occur:

1. El Niño: where the rising cold waters are weakened, leading to more warm tropical water pooling at the surface of the Eastern Pacific. This causes levels of rainfall to decrease in the Western Pacific, over areas such as Australia and Indonesia, and rainfalls to increase over the Eastern Pacific in South America. During an El Niño phase, the winds over the Pacific are weakened, or in some cases start blowing in the opposite direction (becoming “westerly winds”).
2. La Niña: the cold water ocean currents get stronger. This causes levels of rainfall to increase in the Western Pacific and decrease over the Eastern Pacific. The normal easterly winds along the equator become even stronger.
3. Neutral: this is an average state, somewhere in the middle of an El Niño and La Niña.

The name “El Niño” (“the boy child”) was given by South American fishermen who noticed that warm waters often moved north around Christmas time. While this annual change occurs, stronger El Niña and El Niño events tend to occur every 7-10 years and can last months.

In Mexico, El Niño years see relatively cooler and wetter winters, and hotter drier summers. El Niño years tend to also experience a larger number of Pacific hurricanes.