Secular variations of regional rainfall over India

Trends and periodicities in the annual rainfall of 31 meteorological sub-divisions of India based on data for over 60 years have been examined by various latest techniques like Mann-Kendall rank method, low-pass filter and power spectrum analysis. It is seen that the frequency distribution of annual rainfall for the period of 1901 to 1960 is not normally distributed in some sub-divisions of the country. Positive trend is noticed over central India and the adjoining parts of the peninsula and also over two smaller areas in north-west and north-east India. Only over some parts of eastern India there is negative trend. Increase in mean rainfall for 30 years shows a gradient from the west coast to the interior parts of the country with a maximum over the west coast. The spectral analysis of the annual rainfall of these sub-divisions shows a significant cycle of range 8.5 to 12.0 years which is mainly seen in and around the arid and semi-arid regions of Rajasthan, some central parts of India and extreme south peninsula. A cycle of 2.0 to 3.5 years is also observed over large parts of the country mainly over north-west India, central parts of peninsula and some parts of northeast India