DISTRIBUTION AND LONG-TERM FEATURES OF THE SPATIAL VARIATIONS OF THE MOISTURE REGIONS OVER INDIA

Different moisture regions of India exhibit large spatial variations as part of their natural characteristics. In this paper the spatial variations of these regions are studied using annual rainfall data of 306 well-distributed stations for the 114-year period from 1871 to 1984. The distribution characteristics are studied by determining positions of different moisture regions for sufficiently large probabilities using an average probability diagram (APD), which presents variation of the annual rainfall expected with specified exceedance/non-exceedance probabilities with the variation of the mean annual rainfall over India. For determining long-term features of the moisture regions, variations in the boundaries of the moisture regions are examined during all-India deficient/excessive rainfall years as well as during wet/dry epochs identified in the all-India annual rainfall series. It is noticed that boundaries of different moisture regions fluctuate in space along with the annual rainfall over India. During all-India below-normal rainfall years dry regions spread into wet regions, whereas the reverse is the case during above-normal rainfall years. The extremely arid, arid, and semi-arid zones of north-west India have been found to exhibit maximum variations.