Atmospheric rivers and extreme precipitation over India

Abstract

Atmospheric rivers (ARs) are qualitatively described as long, narrow, and transient corridors of strong horizontal moisture transport in the lower troposphere. They are the strongest moisture fluxes in the mid-latitude atmosphere. Upon landfall at coastal or inland regions, ARs exert a diverse range of impacts spanning from beneficial to catastrophic. However, South Asia, particularly India, has seen limited exploration of ARs. This thesis aims to address that gap by investigating ARs and their connection to extreme events in these regions, through three key objectives. First and foremost is to examine the potential role of ARs in the recent second-largest flood in Kerala, South India, on August 2018. This study involves the identification of ARs before and during the flood, examine the factors intensifying precipitation, and pinpoint locations of surplus moisture uptake. There was an intense and long-duration AR during the second week of August, and its perpendicular impact on the Western Ghats amplified AR-moisture depletion. The polar jet trough dipped towards India and strengthened the region’s monsoon trough. High-and-low pressure anomalies over India directed moisture mainly from the north-central and eastern Indian Ocean into the region.