Variability and Predictability of the Northeast India Summer Monsoon Season Rainfall (Neir)

36 Pages Posted: 26 Mar 2022

See all articles by DEVABRAT SHARMA

DEVABRAT SHARMA

Institute of Advanced Study in Science and Technology

Santu Das

Institute of Advanced Study in Science and Technology

Bhupendra Nath Goswami

Cotton University

Abstract

The mesoscale orography over one of the wettest regions of the world makes the Northeast India (NEI) vulnerable to hydrological disasters while sustaining a biodiversity ‘hotspot.’ The monsoon rainy season over the NEI is known to be longer than June-September (JJAS), but an objective definition has been lacking. Also, understanding the drivers and predictability of rainfall variability over the region is key for sustainable development planning and adaptation to increasing disasters in the backdrop of a warming climate, but lacking. Here, using the relationship between rainfall over the region and winds at 850 hPa, we argue that May rainfall is a result of southwesterly monsoon winds. In contrast, we find that the October rain is not from ‘summer monsoon’ as the winds at 850 hPa change to northeasterly from the South-China Sea during October. Therefore, the summer monsoon rainy season over the NEI (NEIR) is from May to September (MJJAS). In contrast to a significant negative relationship between JJAS NEI rainfall and JJAS Central India (CI) rainfall, the MJJAS rainfall over the NEI has no relationship with JJAS CI rainfall or all India summer monsoon rainfall (ISMR). We unravel that (a) the tropical Northwest-Pacific (TNWP) sea surface temperature (SST), (b) the Subtropical Indian Ocean Dipole (SIOD), and (c) the Atlantic Zonal mode (AZM) are potential drivers of the NEIR variability. Causal inference using the PCMCI method indicates that SIOD directly influences NEIR while TNWP SST has a two-way connection with the NEIR. Potential predictability estimates indicate that NEIR is as predictable as CI rainfall at short leads, while at long leads, the ‘potential skill’ of NEIR decreases significantly compared to the CI rainfall. Smaller amplitude of inter-annual variability of NEIR may be responsible for poorer predictability at long leads.

Keywords: NEIR, Potential Predictability, Causality, Internal Variability, TNWP, ITCZ

Suggested Citation

SHARMA, DEVABRAT and Das, Santu and Goswami, Bhupendra Nath, Variability and Predictability of the Northeast India Summer Monsoon Season Rainfall (Neir). Available at SSRN: https://ssrn.com/abstract=4067274 or http://dx.doi.org/10.2139/ssrn.4067274

DEVABRAT SHARMA (Contact Author)

Institute of Advanced Study in Science and Technology ( email )

IASST, Vigyan Path
Paschim Boragaon, Garchuk
Guwahati, ASSAM 781035
India
08011767457 (Phone)
781035 (Fax)

Santu Das

Institute of Advanced Study in Science and Technology ( email )

IASST, Vigyan Path
Paschim Boragaon, Garchuk
Guwahati, Assam 781035
India

Bhupendra Nath Goswami

Cotton University ( email )

Guwahati, 781001
India

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