Reviewing the Oceanic Niño Index (ONI) to Enhance Societal Readiness for El Niño’s Impacts

Abstract

AbstractNOAA’s Oceanic Niño Index (ONI) is used to record for historical purposes the occurrence and duration of El Niño episodes, based on the monitoring of sea surface temperatures (SSTs) in the central Pacific Ocean. The ONI is used to identify the onset of an above average SST threshold that persists for several months, encompassing both the beginning and end of an El Niño episode. The first appearance of an anomalous seasonal value of 0.5 °C suggests with a high probability that an El Niño could emerge, but for heightened warnings, one must wait for several months. In this article, we proposed that the ONI value of 0.7 °C identifies a tipping point at which the El Niño event becomes locked in, which can provide additional lead time for mitigative actions to be taken by societal decision makers. Our preliminary findings suggest that a first appearance of 0.7 °C value could serve as a credible marker of El Niño’s locked-in phase, which can provide additional credibility to the current 0.5 °C El Niño onset indicator for at-risk societies to get ready for El Niño’s foreseeable societal and ecological impacts.