Nonstationarity in determining flow-duration curves aiming water resources permits

ABSTRACT Anthropogenic activities in the watersheds are responsible for land use changes, thus interfering in its rivers flows regimes. Consequently, changes occur in the hydrological series statistical moments, a condition known as nonstationarity. The use of a nonstationary time series can cause relevant errors, misleading and biasing the ongoing analyses. In this manner, this paper evaluates the possible effects of nonstationarity over water availability for water resources permits in six Brazilian gauges, considering the Q95% as reference. Median and seasonal flow-duration curves are employed in two distinct periods, before and after 1969, for all the series. Results suggested that Q95% increased in four gauges and reduced in the remainder two. Moreover, important changes were observed in intermediate flow-durations, suggesting that the variations are not limited to the series extreme values.