Probable precipitation and reference evapotranspiration in Ponta Grossa -PR

Probabilistic studies on estimates of probable values of evapotranspiration of reference and precipitation are of great value for planning, designing and managing several agricultural activities related to water and soil engineering. The objective of the study was to determine the statistical parameters of five probability density functions adjusted to decennial values of precipitation and evapotranspiration of reference, as well as to calculate probable values using the density function of best adjustment, and to determine the magnitude of occurrence for payback periods of 1.33, 4, 5, 10 and 15 years in the city of Ponta Grossa, Paraná state. The Normal, Triangular, Gamma, Exponential and Uniform probability distributions were considered, and the Kolmogorov-Smirnov tests at 5% probability were used to test the adjustment of the probability distributions to the series of data. The Normal (70.3%) and Gamma (29.7%) probability density functions presented the best adjustment to the series of reference evapotranspiration, and the Gamma (59.5%) and Exponential (29.7%) probability density functions presented the best adjustment to the data series of precipitation. Precipitation for a payback period of 1.33 years (75% probability) corresponded to an average of 26.1% (32,4 mm decennial^-1) of the mean decennial precipitation. The probable values of precipitation should be used for simulations of activities in agricultural planning, designing and managing in Ponta Grossa- PR region.