A statistical study on incidence of drought in relation to agricultural production

Abstract

In India about 75 percent of the cultivated area is rainfed and since about 42 per cent of- our food comes from such areas, there is considerable variation in food production depending upon the amount and distribution of rainfall Semi-arid areas where the annual potential evapotranspiration exceeds-the mean—annual rainfall exist in several of our States. In such areas crop fortune depends very much on vagaries of weather: The annual rainfall in these areas is usually less than 75 cm and there occurs sometimes prolonged dry spells within the rainy season. It is then the distribution of rainfall during a season more important than its amount. While the rainfall, coupled with the moisture storage property of soils-ensurethe--moisture supply, the Water loss taking place in the form of evapotranspiration, runoff and deep drainage places an evapotranspirative demand during the growing season. It is, therefore, the- progressive balance. between the receipt and expenditure of the moisture in the soil which creates favourable or unfavourable conditions for successful crop production. One can, thus, with the help of rainfall distribution and potential evapotranspiration values determine conditions for drought for a specific period in relation to a given variety of crop in the region.

Several research workers have attempted to study the various aspects of drought on this basis. Their studies mostly relate to occurrence of dry spells, water availability periods, drought mapping, Palmer indexing and spectrum analysis for assessing and forecasting of drought. These studies have not taken into account the crop yields in determining the agricultural drought.

In the present paper, therefore, data on rainfall and yield of a crop like jowar have been analysed for certain, semi-arid areas of western India for characterising the agricultural drought and its intensity. The recurrence of drought in relation of jowar has also been studied.