Verification of the stationarity of flow series in the Iguaçu River basin

ABSTRACT The purpose of this technical note is to verify the stationarity of flows in the Iguaçu River Basin, considering 14 fluviometric stations. For this purpose, three sets of annual flow series were studied: mean flows, maximum flows and minimum flows of 7 days. Initially, the exploratory analysis of the data was performed, based on the establishment of two points of change of the characteristics of the flows and the accomplishment of statistical tests of equality of mean and variance, parametric and nonparametric. Finally, composite tests were used considering the basin divided into Upper and Lower Iguaçu. In the exploratory analysis of the data, it was concluded that there was apparently a change in the trend of flow rates, part in the 1970s, part in the 1980s. Therefore, the series were divided in two different ways, at the half and at the point suggested in the exploratory analysis. Regarding the statistical tests, the Mann-Whitney test was chosen because it did not depend on the underlying distribution of the flow series, and because the test was highly recommended by other authors. It was concluded that the flow change occurred in a relatively short interval of time, and could be treated as a non-stationarity per hop. In general, the most recent change was downstream of the Uniao da Vitória fluviometric station. A change in the behavior of the mean and maximum flows was evident, however, such phenomenon was not observed in the evaluation of the minimum flows.