Large-scale drivers and ocean-land feedbacks contributing to extreme precipitation during the January 2021 South Kalimantan flood, Indonesia

초록

Severe flooding impacted South Kalimantan from 8 to 15 January 2021, resulting in significant casualties and widespread disruption. This study investigates the meteorological mechanisms underlying the extreme rainfall event by integrating synoptic datasets with mesoscale modeling, utilizing both the standalone Weather Research and Forecasting model and a coupled atmospheric-hydrological model. Results indicate that the event was primarily driven by active cold surges and cross-equatorial northerly surge systems. Convergence zones, formed by the interaction and blockage of these surges with southwesterly winds, were further modulated by the Madden-Julian Oscillation (MJO) and convectively coupled Kelvin waves. Mesoscale analysis, incorporating satellite observations and model outputs, reveals that the extreme rainfall was associated with convective systems propagating from oceanic to inland regions. This propagation was influenced by the diurnal phase of rainfall and modulated by enhanced background winds linked to the MJO and Kelvin waves, although the second peak did not fully conform to typical diurnal timing. Comparative assessment of the standalone and coupled models underscores the potential feedbacks from oceanic and soil moisture conditions to atmospheric processes. These findings highlight the necessity for further sensitivity studies to elucidate the roles of ocean and land surface interactions in convective initiation during extreme rainfall events.

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