Major quasi-periodic fluctuations in the drought indices

Abstract

Modified Palmer drought indices for six district areas, two each from arid, semi-arid and dry subhumid climatic regions of tropical India, have been examined for the fluctuations of drought indices series covering a period of 70 years (1901–1970). Power spectrum analysis of the drought indices series revealed statistically significant quasi-periodicities of 3.3, 6.6, 10 and 20 years with regional preferences. The first two of these periods are close to the two modal peaks of the Southern Oscillation suggesting that the oscillations of the drought indices may be connected to the large-scale atmospheric pressure in the Indo-Pacific region. The other two periods 10 and 20 years are close to the 11-year sunspot cycle and the 22-year double sunspot cycle. The influences of solar activity and the Southern Oscillation on the Indian climate seem to be causal features for introducing these quasi-periodic cycles in drought indices fluctuations.