Modeling of probability in obtaining intensity-duration-frequency relationships of rainfall occurrence for Pelotas, RS, Brazil/ Modelagem da probabilidade das relacoes intensidade-duracao-frequencia de ocorrencia da precipitacao pluvial para Pelotas, RS

Based on historical series, for each locality, equations can characterize the relationship between intensity, duration and frequency of rainfall occurrence. The objective of this study was to present two equations that can describe the occurrence of intense rainfall in Pelotas, RS state, over the period 1982-2015. The two equations were denominated conventional and hybrid, depending on the probabilistic model used. Following the conventional methodology, the parameters of Normal, Log-Normal, Gumbel and Gamma probability distributions were adjusted by the maximum likelihood method for return periods of 2, 5, 10, 20, 25, 50 and 100 years. The maximum intensity values for the hybrid equation were obtained using the empirical model of Weibull, considering return periods of 2, 5, 10, 20 and 25 years. On the other hand, the same theoretical distributions used in the conventional equation were applied to return periods of 50 and 100 years. The Kolmogorov-Smirnov test was used to select the best fitting distribution for the data. In order to verify the information acquired through the Weibull empirical model in comparison to the theoretical distributions, the t-test was applied to the angular coefficients. Significant differences were not verified between the values of maximum rainfall intensities obtained using the two methodologies, for the pre-established durations and return periods. Thus, considering the maximum rainfall intensities values (durations of 5-1440 min) and return periods of 2-100 years in the municipality of Pelotas, RS, Brazil, both the hybrid and the conventional intense rainfall equations can be used. Key words: rainfall records, intense rainfalls, maximum rainfall intensities Com base em series historicas, para cada localidade, equacoes podem caracterizar a relacao entre a intensidade, duracao e frequencia de ocorrencia de precipitacao pluvial. Objetivou-se apresentar duas equacoes para a localidade de Pelotas, RS, no periodo de 1982-2015, uma denominada convencional e outra hibrida, dependendo do modelo probabilistic utilizado. Na metodologia convencional foram ajustados os parametros das distribuicoes de probabilidade Normal, Log-Normal, Gumbel e Gama, pelo metodo da maxima verossimilhan9a, para os periodos de retorno de 2, 5, 10, 20, 25, 50 e 100 anos. Para a equacao hibrida, os valores de intensidade maxima foram obtidos utilizando o modelo empirico de Weibull, nos periodos de retorno de 2, 5, 10, 20, 25 anos. Por outro lado, as mesmas di