Abstract
Abstract The northern coast of Java, Indonesia, frequently experiences coastal flooding, including in Semarang City. On May 23, 2022, a severe coastal flood led to an embankment breach, primarily driven by atmospheric phenomena such as the Boreal Summer Intraseasonal Oscillation (BSISO) which intensified wind speeds and significant wave height (SWH) in the Java Sea. This study investigates wave characteristics during the flooding event using simulations from the Simulating Wave Nearshore (SWAN) model to assess the influence of these atmospheric drivers. The results reveal distinct wave patterns, with wind speed and wave height increasing significantly from May 19 to May 25, 2022. Wind speeds peaked at 10.3 m/s on May 20 and reached 6.5 m/s at the time of the embankment breach on May 23, while SWH reached a maximum of 0.75 m on May 22 and was 0.6 m during the breach. The BSISO 1 and BSISO 2 indices indicated active intraseasonal atmospheric conditions that corresponded with enhanced wave development. These findings provide new insights into the influence of BSISO on wave amplification and coastal flooding in the Java Sea. The study contributes to disaster mitigation and coastal management efforts by highlighting the importance of incorporating intraseasonal atmospheric variability, particularly BSISO, into flood prediction and adaptation strategies.