Assessing El Niño definitions and early warning alerts across Australia, Peru, and the U.S.: implications for disaster risk reduction and climate justice

This study examined how three Pacific Rim countries issued early warning alerts associated with El Niño, the warm phase of the climate cycle, El Niño-Southern Oscillation (ENSO). The El Niño influences hydrometeorological (hydromet) hazards and disaster risk. While many studies focused on the physics and impacts of El Niño, less explored is the quantitative definition and how this influences early warning systems (EWS). Evidence of conflicting definitions creates confusion affecting how El Niño is detected, hindering warning usability, communication and preparedness. Moreover, a definition problem raises questions about climate justice and DRR. To address this gap, the authors conducted desktop reviews of bulletins from national hydromet agencies across Australia, Peru, and the U.S., key countries of varying impacts, to compare definitions of El Niño and La Niña (ENSO's cold phase) and patterns of alerts from 2017 to 2024. 

The findings show that La Niña-related alerts were most frequent in Australia and the U.S., while Peru issued more El Niño-related alerts. Importantly, we show that while the most common warnings between Peru and the U.S. were El Niño-related, these countries also issued conflicting alerts which occurred during significant El Niños, providing evidence of a potential definition problem. They conclude with implications for anticipatory action DRR as well as climate justice.