Study of the behavior of dry and rainy periods in the city of Garanhuns, PE, with an agricultural planning as a goal

Abstract

This study focuses on estimating the probable monthly precipitation with different levels of significance, and to determine the probability of occurrence of dry and rainy periods in Garanhuns, Pernambuco state. The study is based on the data of monthly pluviometric precipitation of one sequence of data that represents the period between the years of 1913 and 1987. Distinguishing criteria of dry and rainy periods are based on four classes of monthly accumulated rains: (D) dry month, from 0 to 50 mm; (NSR) not-so-rainy month, from 50 to 100 mm; (R) rainy month,
from 100 to 200 mm; and (VR) very rainy month with more than 200 mm. It was using theoretical distribution of gamma probability for estimating the probable monthly precipitation, in the probability levels of 90, 80, 75, 70, 60, 50, 40 and 30%. It was possible to conclude that the gamma distribution presented a good adjustment to the values, favoring its use for estimating the probable monthly precipitation. The lower probable precipitations, below 50 mm per month, are recorded in the months of October, November and December, where the irrigated agriculture should be focused. It is also recommended that species and cultivate species of short cycle should be planted in October, and for those with
a long cycle in August, in order to avoid damages during harvesting.