Analysis of the All-India summer monsoon (June to September) rainfall for the period 1871 to 1978 has been made in order to understand the interannual and long-term variability of the monsoon. On a country level, India receives 85.31 cm mean monsoon rainfall which is 78% of the annual rainfall. The coefficient of variation of monsoon rainfall at the country level is 9.5%. The highest and lowest rainfall country level were observed in the years 1961 and 1877 respectively, the range being 41 cm about 48% of the long term average. There are 13/9 years of large-scale deficit/excess in the 108-yr period. There is a continuous rise in the 10-yr mean rainfall from 1899 to 1953. There are four major climatic rainfall periods in the series. Correlogram and spectrum analysis showed significant 14-yr and 2.8-yr cycles respectively in 108-yr series; however detailed exam:mation indicated that these cycles have developed during the last 30 yr of the data period.

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This study is based on all the monsoon depressions that moved westward across India between Calcutta, Allahabad, and Delhi on the right and Gopalpur, Nagpur, and Ahmadabad on the left during July and August for the period 1891-1960. Statistical distributions of 24-hr motion and of the intensity of the depression, the relation between 24-hr motion and concurrent 24-hr rainfall, and the relation between the intensity of the depression and subsequent 24-hr rainfall are examined. In addition, the average rainfall per depression day and its standard deviation, the contribution of depression rainfall to the total rainfall, and the efficiency of the depression as a rain giver are computed. Mean patterns of 24-hr rainfall within 500 km of the center of the depression along longitudes 8 7 ' E , 80°E, and 75'E are obtained, and the main points of difference between them are discussed. In the quadrants to the right of the depression track, the August July & Aug. Percenta e July within the%& Within Outside Within Outside Within Outside July & Aug. 115 10 119 13 234 23 91

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ABSTRACT-Using data from 39 well-distributed and long-record stations over the area, we found gamma distribution to be the most suitable probability model from among the Pearsonian models that show good fit to monthly rainfall in the Asian summer monsoon. We show that the monthly rainfall distribution is not Gaussian and the simple square-root, cube-root, and logarithmic transformations are of limited utility for normalizing the rainfall distribution.A Craig type chart indicates that the rainfall distribution is a Type I distribution or a special or limiting case of this distribution; these distributions are fitted to monthly rainfall, and the goodness-of-fit is tested by the chi-square test. The gamma distribution (Pearson's Type 111), which is a limiting case of Type I distribution and next to the Gaussian distribution in simplicity, gives a good fit to monthly rainfall a t all the stations in each of the summer monsoon months; the Kolmogorov-Smirnov test and the

The total volume of rain-water over India has been computed for each of the years during the period 1871-1978 on the basis of the rainfall data for a fixed network of 306 raingauges. The mean, the standard deviation and the coefficient of variation of the series of annual rain-water volume are 3143 km3, 300 km3 and 9.5 per cent, respectively. The series is homogeneous and random. The serial correlation is 0.013 which is too low to suggest any relationship between successive terms. Gaussian distribution gives a good fit to the series.The series giving the percentage area of the country with a deficiency of 20 per cent or more, as well as the percentage area with an excess of 20 per cent or more have been obtained. These bring out the variability in the deficiency and excess of rain-water over the country during the period. The years of well-marked rain-water deficiencylexcess over India have been identified by utilizing the criterion of 40 per cent or more area under rain-water deficiency/excess. The occurrence of such years has been found to be random and the number of such years in five-year periods appears to be distributed in accordance with the Binomial and the Poisson Probability models.The impact of marked deficiency/excess on the All India Index of food grain prices and A l l India Index of food grain production has been examined. It is found that the impact of well-marked deficiency can generally be seen clearly but that of well-marked excess is seen clearly in some cases only. This is understandable. Overall excess in a year may or may not result in floods which have the potentiality to damage crops. The impact of the well-marked deficiency of 1918 has been maximum.Remedial measures which would make the economy of the country less dependent on the variability of the annual rain-water have been discussed.