Abstract

In the monsoon months of June to December two monsoons seasons are included. They are the South-west Monsoon season (June to September) and North-east Monsoon season (October to December). The possibi- lity of one of these two monsoons being favourable when the other one fails is not entirely ruled out (3). But the North-east Monsoon period is more well-defined and dependable for rains than that of the South-west Monsoon (1).. In the year 1963 sufficient soaking rains of the order of 1.50" were not received on any three or four consecutive days in the period 13th July to 23rd August in the South-west Monsoon season to take up the Adi pattam sowing of dry land cholam crop. Similarly in the month of October in the North-east Monsoon season in 1963 sufficient rains were not received to now dry land Karunganni Cotton crop. The net result was that the area under these two major dry land crops in and round about Coimbatore was considerably low in 1963, particularly in the case of cholam crop. To know as to whether similar agricultural failure of rains in the critical periods of both the monsoon seasons has occurred previously at Coimbatore, the daily rainfall data, collected in the Observatory, located at the Agricultural College and Research Institute in the period 1907 to 1963 (57 years) were compiled and critically examined with special reference to the occurrence of droughty weeks in general and spells of continuously droughty weeks of four and above in particular. If the rainfall in a week is equal to half the normal rainfall or less, then that week is considered as a week of drought'. Drought has great agri- cultural significance when it lasts for four or more consecutive weeks (2)

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