Sea level extremes and compounding marine heatwaves in coastal Indonesia

Low-lying island nations like Indonesia are vulnerable to sea level Height EXtremes (HEXs). When compounded by marine heatwaves, HEXs have larger ecological and societal impact. Here we combine observations with model simulations, to investigate the HEXs and Compound Height-Heat Extremes (CHHEXs) along the Indian Ocean coast of Indonesia in recent decades. We find that anthropogenic sea level rise combined with decadal climate variability causes increased occurrence of HEXs during 2010-2017. Both HEXs and CHHEXs are driven by equatorial westerly and longshore northwesterly wind anomalies. For most HEXs, which occur during December-March, downwelling favorable northwest monsoon winds are enhanced but enhanced vertical mixing limits surface warming. For most CHHEXs, wind anomalies associated with a negative Indian Ocean Dipole (IOD) and co-occurring La Nina weaken the southeasterlies and cooling from coastal upwelling during May-June and November-December. Our findings emphasize the important interplay between anthropogenic warming and climate variability in affecting regional extremes. Increased extreme high sea level events and concurrence of marine heatwaves are observed along the Indian Ocean coast of Indonesia in the past decade due to the combined impact of anthropogenic warming and natural decadal climate variability.

Automated summary

This study investigates extreme sea level height events and their relationship with climate variability along the Indian Ocean coast of Indonesia in recent decades. The findings highlight the interplay between anthropogenic warming and climate variability in affecting regional extremes, with increased high sea level events and concurrent marine heatwaves observed in the past decade.