Heavy precipitation and Flooding associated with Atmospheric Rivers over the Indian Region

Atmospheric Rivers (AR) are long plumes of intense water vapor transport in the lower atmosphere that carry most of the atmospheric water vapor fluxes from the lower latitudes to the higher latitudes. Landfalling ARs are a major source of heavy precipitation and often cause major weather and/or hydro-meteorological extremes. An AR detection algorithm is applied to identify and characterize these features using gridded fields of anomalous vertically integrated water vapor transport (IVT) over Indian region. The underlying theme of this study is to understand the impacts of ARs on extreme precipitation and floods over the Indian region.

Seasonal analysis of AR incidence over Indian coastal regions using AR global database is performed for the period spanning 1980 to 2015. The results highlight that ARs exist and causes heavy precipitation events (HPEs) during the summer monsoon (June-September) over the West Coast of India and during the winter monsoon (October-December) over the East Coast of India. The analysis of relationship between the frequency of ARs and three prominent large-scale atmospheric modes (SOI, Nino3.4, and IOD) suggest that most of the west coast region, SOI, Nino3.4 and IOD can be helpful in describing the frequency of ARs in summer monsoon, which in turn can be useful to characterize the frequency of HPEs over the Indian region. The study also investigates the detection of ARs over the Indian region through the integrated water vapor transport (IVT) thresholds using long-term (1979-2013) atmospheric reanalysis product. The results highlight that the existence of both landfalling and inland penetrating persistent ARs from the Arabian Sea as well as Bay of Bengal sides lead to HPEs and floods over the Indian region. A statistically significant correlation between IVT of ARs and extreme precipitation emphasizes the role of ARs as a proxy in identifying the occurrence of HPEs and floods over the Indian region.

The modelling capability in the prediction of occurrence of ARs and associated HPEs with different physics schemes are also explored. The results reasonably predicted the occurrence and location of ARs and the rainfall over the west coast of India.

Keywords: Atmospheric Rivers, Heavy Precipitation Events, Floods, Climate indices, Indian region