Charting Niño 3.4 sea surface temperature anomalies

Produced by Sanden Totten and Chris Keller | Published Jan. 10, 2017

An El Niño occurs when water in a large swath of the Pacific Ocean along the equator heats up more than average. This is measured by looking at sea surface temperature anomalies, or fluctuations in ocean temperature, in key parts of the ocean. One of the most important areas is a region called Niño 3.4.

If temperatures there reach 0.5°C above average for at least three consecutive months, then an El Niño has formed. Not all El Niños are equal though, only the strong ones tend to bring rain to Southern California.

The 1997-98 El Niño is considered one of the strongest on record. Parts of California saw double the average rainfall, leading to floods and mudslides that caused $550 million in damages.

The chart below displays the deviation from the sea surface temperature baseline in the Niño 3.4 region during strong El Niños dating back to 1990. Click the filters on the right to explore data for other years in this region.