Low-lying island nations like Indonesia are vulnerable to extreme sea level events. Rapid urbanization of Java island and population growth in low-lying areas, together with fast sinking due to ground water extraction (e.g., Jakarta is the fastest sinking city in the world), further increase vulnerability to climate variability and change, making the problem of rising sea level particularly acute in this region.

By analyzing tide gauge and satellite observations we detect the Height EXtreme (HEX) events around Indonesian coasts of the Indian Ocean since 1993, when accelerated global sea level rise (GSLR) has been detected and attributed largely to human-induced climate change. To put our analysis in a longer-term context, we also extend our analysis to the 1960s using reanalysis data. To attribute the causes for the HEX activities, we perform model experiments using two independent ocean general circulation models and a coupled global earth system model, the CESM1. Additionally, the results from CMIP6 are also analyzed to estimate the impacts of external forcing on Indonesian regional sea level change. We find that most HEX events occur during the 8yr period of 2010-2017, with the highest monthly magnitude of 0.44m. Anthropogenically-induced GSLR and positive decadal sea level anomaly (SLA) combine to boost up the HEXs for this period. The positive decadal SLA is mainly driven by the equatorial westerly and longshore northwesterly wind anomalies over the Indian Ocean, which are associated with the decadal variabilities of ENSO and the Indian Ocean Dipole (IOD). Our findings show the crucial roles played by anthropogenic warming and decadal climate variability in shaping the extremes, which may help improve decadal predictions and near-term projections of the high impact sea level rise events.