Evolution of Marine Heatwave in the Philippines During and After the 2023/24 El Niño

Abstract In March 2023, the Philippine Atmospheric, Geophysical & Astronomical Services Administration (PAGASA) issued an El Niño watch that was expected to commence in July-August 2023 in the tropical Pacific. The El Niño event lasted until May 2024, which coincided with the declaration of the 4th global coral bleaching event by NOAA in April 2024. In the Philippines, the impacts of this event through much warmer sea surface temperatures (SSTs) were experienced even after the El Niño from June-August 2024. At the same time, daily SSTs reached a record high in November 2023 and from April-May 2024, surpassing recorded SSTs from previous El Niño events such as the 2015-2016 El Niño. In this study, we tried to investigate how the marine heatwave that resulted from warmer SSTs brought by El Niño evolved in the waters surrounding the Philippines during and after the El Niño event. Marine heatwaves are “prolonged, anomalously warm water events” that have caused significant impacts on marine organisms globally yet there is limited information on how marine heatwaves are related to El Niño events in the Philippines. We used the Operational Sea Surface Temperature and Ice Analysis Near Real-Time (OSTIA-NRT) dataset from March 2023 to August 2024 to examine the spatiotemporal evolution of SSTs and the marine heatwave anomalies during the recent El Niño event. Results of the study are expected to contribute to understanding marine heatwaves in the Philippines, specifically during an El Niño event. Marine heatwaves have been documented to have detrimental effects on marine ecosystems globally. Understanding their causes and links to broader climate change patterns can provide guidance for marine conservation efforts.