Duration of the rainy season and occurrence of dry spells in the Basin of the Parnaíba River

Abstract

This article search contribute for demarcation of the beginning and end of the rainy season and evaluation of the frequency and intensity of dry spells in the Basin of the Parnaíba River, which covers areas of the states of Goiás, Minas Gerais, Distrito Federal and Mato Grosso do Sul. The understanding of this subject is particularly useful for the understanding of the rainfall rhythm of the basin, being able to subsidize the planning and management of economic activities vulnerable in relation to the rhythm of water offer. Was used the historical series of twenty-two rain gaugesof the Agência Nacional de Águas (ANA), corresponding to the period 1973-2011 (38 years).To delimit the rainy season was adopted criterias with base in the amount and continuity of the rainfalls. In the case of dry spells was based on summation of days interiors of the rainy season without precipitations or that they have been equals or lower to half the daily evapotranpiration. It was found that the rainy season occurs, on average, from 28 October to 02 April, although there are specificities, highlighting Brasilia and its surroundings and the eastern basin. As for the dry spells, the most worrisome months are January and February, because, despite receiving rainfall totals monthly more expressives, recorded the highest number of events, especially more long.