Unravelling the influence of teleconnection patterns on monsoon extreme precipitation indices over the Sikkim Himalayas and West Bengal

The influence of major climate indices of tropical seas and equatorial oceans on the variability of monsoon (June to September) extreme precipitation indices (EPIs) is explored for observed (1961-2017) period over two meteorological subdivisions of India. The strength and span of covariate relations for each EPI and the Indian Ocean Dipole (IOD), the Multivariate El Nin similar to o-Southern Oscillation Index (MEI), the Pacific Decadal Oscillation (PDO), the Southern Oscillation Index (SOI), and sea surface temperature (SST) anomaly of the Bay of Bengal (SST-BoB) as well as the Arabian Sea (SST-AS) are evaluated by linear and nonlinear functions. The periodicities and coherent patterns of each EPI and the climate indices are investigated in time-frequency space using wavelet power spectra. This is to identify the periodic behaviour, strength of nonlinear linkages and major climatic factors involved in the variability of monsoon precipitation extremes. EPIs show significant negative association for MEI and SST-AS. Consecutive dry days (CDD) develop significant positive (negative) correlation with MEI (SST-BoB) over Bihar, GWB, Orissa, Jharkhand and Sub-Himalayan West Bengal (SWB). The duration, intensity and absolute indices over the Sikkim (SIK) Himalayas exhibit significant negative correlation with the SST-BoB. The EPIs develop significant positive relation with PDO phases across the regions. EPIs show asymmetric cor-relation pattern for SST-BoB and SST-AS with the changes in latitudes and altitudes. Interannual periodic bands from low to medium frequency regions are observed in EPIs. CDD shows in-phase coherency with MEI, and a complex periodic oscillation with SST-BoB. Consecutive wet days (CWD) develop strong consistent decadal co-herency with IOD. Monsoon total precipitation (PRCPTOT) is dominantly influenced by MEI and SST-BoB. Heavy precipitation events show strong response to the MEI and SST-AS over GWB. Absolute indices show regional variability in power spectra with intermittent breaks. For absolute indices, major controlling factors considerably vary at both subdivisions and timescales. This study reveals corresponding changes in active-and break-spells, drought and flood events, regional availability of water resources and its possible consequences.