Ajuste da distribuição gama aos dados de precipitação pluvial do Município de Lavras Estado de Minas Gerais

Abstract

An experimental work was conducted with the objective ofpresenting a detailed study on the application of gamma distribution applied to the rainfall analysis data for the county of Lavras, Minas Gerais. Daily rain precipitation data (mm) relative to period going from 1966 to 1996 was used in the experiment. Observations concemed to the clustered datafor the periods ranging from 1-3, 1-6, 1-9, 1-12, 1-15, 1-18, 1-21, 1-24, 1-27 and also for the monthly totais were utilized. Foreach period, itwas estimated the parameters (a, p), their variances and confidence intervals, the estimatives of average rainfall and variances, the proportion of null values and coefficient of assimetry. The chisquare was done to verify the adjustment of sampling data to the gamma distribution. Na estimation for the probable rainfall occurences was associated with 19 leveis of probability. The statistical analysis were performed using a SAS program. The main conclusions regarding to the study were: in 65% of the studied periods the data fitted to a gamma distribuition; the estimatives of a parameters of (a) were smaller in the wettest month and greates in the driest month, increasing in valueto the size of the period increased; the estimatives of the parameter of(p) scale didn't present a well defíned trend withna increasing size ofthe periods; as the size ofthe period increased there was a trend for the data to fít betterto the gamma distribuition, daily data didn't fit to the gamma distribuition. There is a 10% probability to the occura rainfall up to 281,0 mm in the month of march and 90% probability to have a rainfall up to 79,8 mm in the same month.