Abstract

                                A systematic study was made to assess the variability and probability occurrence (initial and conditional) of rainfall at Coimbatore. Length of Growing Period (LGP) was also computed to plan dry land crop cultivation with minimum risk. LGP was computed by two different methods viz., weekly Moisture Availability Index (MAI) and weekly Rainfall /Potential Evaporation (R/PE) ratio. The mean weekly rainfall and PET data from 1961-2010 were used to compute LGP. The results indicated that for getting more than 25 mm with 50 per cent probability was possible from 42ndto 45th Standard Meteorological Week (SMW). The chance of receiving 20 mm rainfall per week with 50 per cent probability was observed from 39th to 49th week except in 48th week. The coefficient of variation was below 150 per cent from 16th to 23rd week and from 37th to 45th week. It showed that weekly rainfall during pre-monsoon and post monsoon season is highly dependable. LGP analysis shows that 77 days (37th to 47th week) was available as per MAI method and 91 days (37th to 49th week) period as per R/PE ratio.

Key words : Co-efficient of variation, Conditional probability, Initial probability, LGP, Rainfall analysis