Probability models for weekly rainfall at Thrissur
Keywords:
Southwest monsoon, Northeast monsoon, Assured rainfall, Dependable rainfallAbstract
Probability distributions were fitted for rainfall in the different standard meteorological weeks (SMWs) at Thrissur, using daily rainfall data for 31 years from 1980 to 2010, recorded at Agromet observatory, Vellanikkara. Exponential distribution was suitable for 16 SMWs, normal distribution for 10 SMWs and lognormal for 8 SMWs. The probabilities for more than 10, 20, 30 and 40 mm rainfall in the different standard weeks were estimated based on the distributions. Heavy rainfall is obtained from 23rd to 31st SMWs during 4th June to 5th August as indicated by the probabilities. The excess rainfall during this period should be harvested and stored for irrigation in the SMWs with less than 75 percent probability for even 10 mm rainfall. In northeast monsoon season (October-November), more than 75 percent probability for 30 mm rainfall is only during 15th to 21st October. Hence supplementary irrigation is needed for rabi crops raised in this season. The assured rainfall amounts at 75 and 90 percent probabilities in the different SMWs were computed based on the probability distributions fitted. The dependable rainfall is found to be more than 40 mm during 4th June to 5th August. 11th to 17th June is the rainiest week at Thrissur. From 35th to 39th SMWs coming in September, assured rainfall is less than 20 mm. During 1st October to 11th November of northeast monsoon season, dependable rainfall is in the range 12-32 mm. The probabilities for different amounts of rainfall along with assured rainfall amounts in the different SMWs serve as a guide for planning various agricultural activities in Thrissur.Downloads
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