Probability of occurrence of water deficits and excess on the climatic conditions of Barreiras, Bahia

Abstract

Probabilistic studies of climatic variables are of utmost importance for the planning of agricultural activities. In this context, we aimed to adjust the function Normal distribution to the values of precipitation and monthly potential evapotranspiration in order to determine the components of the water balance (deficits and excesses) with different levels of probabilities in Barreiras, Bahia. We used daily data of maximum and minimum air temperature and precipitation, period of 1961 to 2008. The potential evapotranspiration was estimated by the method of THORNTHWAITE (1948). In order to check the adherence of the estimated probabilities to the observed frequencies, we applied the adherence tests Chi-square (χ2) and Kolmogorov-Smirnov (KS), at 5% of significance. We obtained the probable values of precipitation and monthly potential evapotranspiration for the following probabilistic levels: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 and 90%, correspondent to the probable minimal occurrence P(X > x). We elaborated for each probability level of precipitation and potential evapotranspiration a monthly water balance, according to THORNTHWAITE and MATHER (1955). The use of Normal distribution presented better adjustment to the data of precipitation and monthly potential evapotranspiration by applying the KS test, at 5% of significance. At the level of 75% probability, the major values of water deficit concentrated in the period of April to October, with the need of total replacement of 579.1 mm.