Interference of significant sub-decadal periodicities in Indian monsoon rainfall

The inter-decadal variability of the Indian Summer Monsoon Rainfall (ISMR) has been conventionally considered to be an important indicator of climate change. This variability can be studied in terms of the significant periodicities underlying the rainfall time series. The present endeavour implements the Welch technique to estimate the Power Spectral Density (PSD) of rainfall data of the period of 1901–2005 to identify the significant periodicities at all India and at \({1}^{0} \times {1}^{0}\) gridded scale. The analysis reveals that the sub-decadal periodicities in the ranges of (2, 3), (3, 5) and (5, 10) years have prevailed over 54%, 30% and 26%, respectively, of the subcontinental stretch individually, and about 82% of the total land area by combined action over the last century. Driven by the need to determine the interplay of these dominant sub-decadal periodicities in causing extreme rainfall occurrences this work seeks to correlate their interference patterns with the recorded rainfall amount. The results show the presence of a linear relationship within the range (0.5, 1) across diverse combinations of sub-decadal periodicities.