Study on the Pattern of Rainfall Distribution using Some Competing Probability Distribution in Cooch Behar District of West Bengal

DEPARTMENT OF STATISTICS Faculty of Agricultural Uttar Banga Krishi Viswavidyalaya Pundibari, Cooch Behar, West Bengal-736165 Study on the pattern of rainfall distribution using some competing probability distribution in Cooch Behar district of West Bengal Rakesh Kumar Meena1, Sharda Dubey1 and S. Basak2 The climate of the Cooch Behar district of west Bengal, in general, is sub-tropical per humid to tropical humid in nature with distinctive characteristics of high rainfall, high relative humidity and low temperature. About 70 % of the annual rainfall is received during the southwest monsoon season, June being the rainiest month. On an average there are about 102 rainy days with records of more than 400 mm rainfall in 24 hours. During monsoons, starting from June, Cooch Behar experiences heavy rainfall. The average annual rainfall is about 3201mm in Cooch Behar district of West Bengal. The numbers of rainy days in Cooch Behar district is recorded to be the highest in the months of June and July. In Cooch Behar district, the number of rainy days often crossed 20 in a month during the months of June and July followed by 15-20 in August and September. Which during April, May and October is varies maintaining a central tendency towards 10 in each month. Also the above mentioned information is based on rainfall data of 1971-1981. An early onset of pre- monsoon shower and occurrence of a low quantum of precipitation during the month of March and April with occasional short dry spells are the other distinctive characteristics for the district of Cooch Behar. During 1995 to 2015 the onset of effective monsoon is delayed by one month as compared to the study period of 1971-1990. Assumed the arrival of monsoon rains over this part of West Bengal has relation with the onset of monsoon at Kerala. As a result, contrary to other parts of West Bengal, The observed variation in the OEM date is only 4 days as compared to 9 days for the period of 1971-1990. However the variation in EEM dates for both of the periods is same. there is possibility of occurrence of dry spell of 10 days or more once in every year, on the average, the starting date of this dry spell being any time during around 1st and 2nd week of May, i. e.10days from the day of onset of monsoon. Again, such a dry spell may appear once in every year, on the average, around 2nd and 3rd week of September. There is also possibility of another such spell of dry days in this area in every in every year, on the average, anytime during 2nd and 4th week of October, The average number of dry spell per year is found to be more in comparison to the study period of 1971-1990. The average amount of rainfall observed in OEM week are almost same for both of the periods but during 1995-2015 it is less than half of the rainfall in EEM week during 1971-1990, The ability of the gamma distribution and parameter estimates to adequately fit the empirical distribution of values in the entire study period have been tested using the KS goodness of fit test. Gamma and Weibull distributions are the best fitted distributions for the rainfall years in Terai region of Cooch Behar district of West Bengal. Observed critical dry spell duration can be used as an indicator of drought risk. This research could prove valuable to a wide range of groups from scientists studying precipitation, to policy makers assessing forecast information, to farmers in crop planning. Probability Distribution, Rainfall Distribution, Gamma Distribution, M. L. E Estimation of Gamma, Oem& Eem