Agroclimatic classification of the semi-arid tropics IV. Classification of India, Senegal and Upper Volta

To arrange the 190 locations in India, Senegal and Upper Volta into finite groups, numerical taxonomic techniques were adopted, using 11 agroclimatic variables derived from parts I, II and III of this study. The results obtained using the data matrix of 7 principal coordinates with Euclidean metric — unweighted pair group method using arithmetic averages (UPGMA) fusion strategy appear to be the most suitable to identify groups formed in India and West Africa. In general, this study separated the highly undependable locations with different effective rainy periods. The groups identified are not homogeneous in terms of dependability defining dry-seeding feasibility, at the lower end of the range, and water-logging hazards. Therefore, to overcome this problem, the groups were first arranged into 3 broad zones, namely arid, semi-arid and sub-humid according to a modified Thornthwaite approach, and the semi-arid locations were further divided into 5 zones based on the effective rainy period related to the cropping pattern. As the primary groupings refer to the most stable situation, they were again divided into 5 sub-zones each based on the level of dependability, which was characterized by the standard deviation of the commencement time of sowing rains. To account for some of the operational problems, such as water-logging, availability of field work days for cultural operations, etc., they were further divided into groups and sub-groups based on wet and dry spells and aridity index.

The derived zones and sub-zones of the semi-arid tropics are straight forward and easily memorised, and make sense agronomically. With the given classification structure it is easy to add new locations without further numerical analysis.