资源环境科技发展态势分析平台

A multi-day atmospheric river (AR) in the second week of August 2018 was pivotal in causing extreme precipitation over south-west coast of India that eventually lead to record-breaking floods in the state of Kerala. Integrated water vapor transport (IVT) analysis depicted an intense and long-duration CAT 5 atmospheric river stretching from the Arabian Sea across South India into the Bay of Bengal. A high-pressure ridge over the eastern Arabian Sea and western India and a trough over the Bay of Bengal forming a subsection of monsoon wave-train was observed ahead of the flood event. The monsoon trough was exacerbated by the synchronous effect of a polar westerly jet trough that created an anomalous low-pressure region covering central and eastern India and a quasi-stationary depression over the Bay of Bengal. The system favored continuous supply of moisture from the Indian Ocean into Kerala. To locate major sources of moisture, the air parcels that rained out to generate extreme precipitation are tracked backwards using the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT). The backward trajectory analyses reveal that on 13th August more than 60% of the moisture was contributed from the Central-Eastern Indian Ocean, with some intermittent contributions from the Arabian Sea; while on 14th–16th August, about 25–30% was contributed from the Arabian Sea