Variabilidade do início e fim da estação chuvosa e ocorrência de veranicos na bacia hidrográfica do Rio Paranaíba

Abstract

The knowledge of climate is essential for planning and managing of the use of the natural resources, including water. This is especially important for the watershed of the Parnaíba River, since the agricultural sector is very important to its economy. Therefore, it is necessary to study its rainfall in a special way in relation to the duration of the rainy season, which concentrates for over 85% of the total annual the rainfall. It is also important to analyze the occurrence of dry spells, that interferes in the pace of the water availability for both the dynamics of the environment as for human activities. The Parnaíba Basin is relatively diverse of the point of view altimetry, which influences in the mesoclimates, creating specific situations that need to be understood and considered. This research drew on historical series of 22 pluviometrics stations of the Agência Nacional de Águas (ANA), corresponding to the period of 1973-2011 (38 years). Were prepared the water balances according with Thornthwaite & Matter (1955), necessary for defining the beginning and end of the rainy season of each year and too for count and characterize of the dry spells. It was observed that the rainfall concentrated, usually between the months of October and March. The average date of outset of the rainy season is October 28 and the average date of the end of the rainy season is April 2. Despite of the relatively generalized tendency of the beginning and end of the rainy season, there are important specificities within the basin, especially Brasilia and its surroundings and the east of the Alto Paranaíba. These areas have the larger durations of the rainy season as well as the larger rainfall index. On the other hand, the stations of Corumbazul (municipality of Buriti Alegre-GO) and Itajá (municipality Itajá-GO) have rainfall station more shorter and receive smaller amounts of rain. Occured 3336 dry spells during the period 1973-2011 and that 36% their lasted of 7 to 8 days. With the exception of the station rainfall Turvânia-GO, all localities have events of dry spells exceeding 18 days, which can be very prejudicial for economic activities of the basin. The most troubling months are January and February, which despite of have monthly rainfall totals expressive are the months that occur the largest number of dry spells. In the range of 13 to 18 days in January, ocurred 72 events of dry spells, equivalent to 11,9% probability and in February occurred 77 events, corresponding to 10,7% probability. And in relation to dry spells above of 18 days, it was found that in January occurred 30 events (5% probability) and in February 43 (6% probability). The understanding of such a situation is particularly useful for understanding of the climatic rhythm of the Paranaíba Basin, can subsidize the planning and management of the same, offering subsidies for necessary consideration of the temporal variability of water ingress in the your hydrographic system.