Annual rain‐water over India, its variability and impact on the economy

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Abstract
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 deficiency/excess 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 All 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.

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