Agroclimatic classification of the semi-arid tropics II. Identification of classificatory variables

Eight agroclimatic variables related to crop production potential in the semi-arid tropics of India are identified. These are used to assess dry-seeding feasibility, water-logging hazard, risk in agricultural production, cropping patterns and their spatial distribution, using data from 80 locations in India. Regression analysis has been used to identify differences between locations at different scales, i.e., local differences caused by orography, regional differences associated with circulation patterns and continental differences associated with general circulation patterns. Using the data of 8 variables from 199 locations in India and two west African countries (Senegal and Upper Volta) three dissimilarity parameters were derived. The basic dissimilarity observed on a continental scale is that for the same amount of mean annual rainfall the growing season is longer in west Africa than in India. Thus, in west Africa the corresponding wet and dry spells within the available effective rainy period are quite different from India. This will have a significant influence on farming systems in general, and on the identification of adopted crop/cropping systems in particular.