Design of an Innovative Probability Plotting Position For a 73 Year Precipitation Data (1940-2012) of El Paso County, Texas, U.S.A
Héctor Adolfo Quevedo, Abraham López, Iván Alvarado

Abstract
This research established a tridimensional probability plotting position, as a function of annual precipitation data, probability of occurrence and return periods. The study determined the gamma distribution to be the most suitable one fitting the data, using the Minitab computer program based on the value of the Anderson-Darling test, which turned out to be 0.271. Afterwards, this method constructed a probability graph going as a function of precipitation values, probability of occurrence and return periods. This novelty approach has an advantage over the traditional plotting positions methods, because it first identifies the right probability distribution and, on that graph constructs a probability plotting position, as a function of precipitation data, probability of occurrence and return periods. This task was done without relying on the traditional assigning of ranges to the data (that not always follow the normal distribution), and the use of empirical formulas. It is concluded that this approach is more precise and reliable than the traditional plotting positions methods, because it determines optimum estimates for return periods and occurrence probabilities that helps in the construction of prime hydraulic projects.

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