Evaluation of agricultural drought using probability distribution of soil moisture index

Abstract

Weekly soil moisture budget was worked out for kharif cropping season July through October for 33 years (1940-1972) for Delhi which has a semi-arid monsoonal climate. For this purpose the step function approach using climatological data suggested by Slatyer (1960) was followed. Soil moisture index (SMI), the ratio of available water to available water 'capacity in the soil root zone is directly related to the ratio of actual and potential evapotranspiration. frequency distribution of weekly SMI values were evaluated and compared with the Beta distribution. Kolmogorov-Smirnov test of goodness of fit indicated the Beta distribution to be a suitable statistical model for approximating the frequency distribut.ion of SMI for the monsoon season.

For the threshold values corresponding to agricultural drought as well as potential moisture conditions in the root zone in respect of kharif crops, viz., sorghum, pearlmi1let, corn, paddy and peanut crops grown in the Delhi region, the frequency of occurrence of agricultural drought during the monsoon season in the different phenological stages was determined. These results are discussed with reference to selection of a cropping pattern tailored to rainfall distribution of the region.