Trend and spectral analysis of rainfall over India during 1901–2000

Abstract

[1] The spectral analysis of gridded rainfall data obtained from 1384 rain gauge stations by India Meteorological Department demonstrates not much change in low-frequency components of decadal spectra of all India and its four subregions, namely, southwest, southeast, central, and northwest, during the last 10 decades. However, the dominant as well as the significant cycles lying between the periods 10–20 days, 20–30 days, 30–40 days, and 40–50 days are highly variable on an interdecadal basis. On close inspection, it can be inferred that the 40–50 day oscillations that corresponds to Madden-Julian Oscillations is mainly associated with the southern Indian region, namely southwest and southeast, and the 30–40 day oscillation of southeast region is gradually increasing on a decadal scale during the last 4 decades. The physical context of interdecadal variability of rainfall in India can be linked with the warm phase of Atlantic multidecadal oscillations and the cold phase of interdecadal Pacific oscillations. The correlogram analysis shows the presence of 15, (17, 19), and 17 year cycles for the southwest, central, and northwest regions, respectively. No significant trend is discernable during the last 10 decades, when the linear least squares fitting method and Mann-Kendall statistic to identify the trend and the normalized test statistic and statistical probability to quantify the significance of the trend are applied, on the annual rainfall data for all India and its subregions.