A multiscale analysis of the extreme rainfall triggering flood and landslide events over Bengkulu on 27th April 2019

On 26 - 27 April 2019, torrential rains triggered floods and landslides on the Indonesian island of Sumatra, particularly in Bengkulu Province. This extreme event resulted in many casualties and displaced thousands of people. At least nine districts were affected, including Bengkulu city, Kaur, North Bengkulu, Central Bengkulu, South Bengkulu, Seluma, Kepahiang, Lebong, and Rejang Lebong. Rain gauges in Bengkulu measured daily rainfall of 81 to 225 mm on 27 April 2019, with minimum and maximum rainfall were observed at Fatmawati station and Batu Roto station, respectively. This study aims to investigate the possible causes of extreme rainfall by analyzing the multiple timescales of atmospheric conditions. The subseasonal tropical waves of Madden-Julian Oscillation (MJO) were strong and active (Phase 3) during the event causing strong convection and heavy rainfall. Besides, the Equatorial Rossby (ER) waves were also active, which typically indicated by two low pressures at the north and south of Sumatra. The southern low pressure was known as the Tropical Cyclone Lorna that contributing to heavy rainfall and strong winds toward Bengkulu. Weather radar images in Bengkulu showed the eastward propagation of torrential rains from the Indian Ocean to Bengkulu, which depicts a typical diurnal cycle over Bengkulu. On 26 April 2019 at 08 LT, heavy rainfall was observed in the Indian Ocean moving eastward. At 14 LT, Bengkulu was hit by the torrential rains until night, which caused the floods and landslide on 27 April 2019 at 01 LT.