Extreme precipitation over complex terrain using multiple remote sensing observation: A case study in the Great Bandung, Indonesia

Intense precipitation events are the main cause triggering hydrometeorological hazards over complex terrain. Two extreme precipitation (EP) events led to major flooding on 23-25 March 2021 and produced a rain-hail mixture (RHM) on 11 April 2021 in the Greater Bandung (GB) basin area, Indonesia. We investigated the spatial and vertical structure of precipitating cloud systems and the plausible mechanism triggering the two case studies with combined multiple remote sensing observations using an X-band polarimetric Doppler Weather Radar (Xpol) and Xband rain scanner radar (RSR) network, supported by rain gauges and satellite observation. The local processes controlling the intense rainfall events over the complex topography were quantified for the first time using an observational campaign in Indonesia. During the first EP event (23-25 March 2021), the modified satellite algorithm successively confirmed that the mesoscale convective system triggered the local anomalous circulation. The RSR network reveals that the EP in eastern GB contributed to the overflow of the Citarum River alongside the basin, coinciding with the eastward propagating convective system that produced oblate-shaped water droplets without hail. Nevertheless, during the second EP event on 11 April 2021, the strengthening of mountain-based convection played a main role in producing RHM, confirmed by a hail differential reflectivity larger than 12 dB and exhibited hail early stage over two height levels in different locations (981 m and 1033 m) in the GB. Our study also found Doppler vorticity-based and rain sizes combination indicators using RSR data networks in capturing such extreme weather events over complex topography with 35 min early times to support the early warning system of hydrometeorological disaster mitigation over GB, Indonesia.