Ideal size of minimum annual flow historical series and its applications in hydrological studies: case study in the Paraná and São Francisco Hydrographic Regions

ABSTRACT

The use of historical series of hydrological records is one of the basic tools for the management of water resources. However, several regions do not have long historical records. Thus, the general objective of this study was to define the ideal sample series size for historical series of minimum flows. Nineteen fluviometric stations from the Paraná Hydrographic Region (RHP) and another 35 from the São Francisco Hydrographic Region (RHSF) were used, with the criterion of having at least 50 years of daily data records. Annual minimum series were generated for each of the stations, to which the non-parametric tests of randomness, stationarity, independence and homogeneity were applied, in order to verify the possibility of applying probability distributions to the data. Then, the Kolmogorov-Smirnov adherence test was applied in order to verify the best fitted distribution for each station. The Q₇ and the permanence flow series were constituted for the complete and specific (partial) series, making it possible to obtain the values of means, Q_7,10, and Q_90% of each series. The results obtained through the complete and specific series were statistically compared using the PBIAS and Student's t test. The study showed that, in general, the results obtained through series of seven to fifteen years were satisfactory, or statistically equal, to the results of the complete series, which may indicate that not always having few daily record data of hydrological series makes the necessary studies unfeasible.

Keywords:
hydrological cycle; water resource management; hydrographic basin