Statistical study on incidence of drought in relation to agricultural production

Abstract

In India about 75 per cent of the cultivated area is rainfed and since about 42 per cent of India 's food comes from such areas, there is considerable variation in food production depending upon the amount and distribution of rainfall. The annual rainfall in India 's semi-arid areas is usually less than 75 cm and there sometimes occur prolonged dry spells within the rainy season. An agricultural drought is caused by a rainfall deficiency spread over a long duration during the crop season. The intensity of drought is related to the duration of the period during which total rainfall is deficient in relation to that required by the crop for its growth. Conditions for drought for a specific period in relation to a given variety of crop in the region may be determined with the help of rainfall distribution and potential evapotranspiration values. The agricultural drought and its intensity were characterized using data on rainfall and yield of a crop like jowar for certain semi-arid areas of western India. The estimates of the minimum amount of rainfall which is just sufficient for crop growth during a given number of consective weeks were worked out. The occurrence of rainfall below these drought base values gives rise to drought conditions. These values were used to determine the probability estimates of the occurrence of drought of varying durations. In Jamnagar and Surendra Nagar, the occurrence of drought of 9 week duration during early August and end of September is relatively more frequent and is expected to occur once in four and five years respectively.