Abstract
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.