Low-Flow Seasonality and Effects on Water Availability throughout the River Network

Given the increasing demand, there is a constant need to identify ways to optimize water use without imposing drought risks and conflicts for its use. The water availability, represented by low flows, is used as a criterion to grant water use by regulators. Therefore, the objective here was to investigate the effects on water availability considering annual and monthly estimates of two low flows: the low flow observed for 7 consecutive days with a return period of 10 years (Q7,10) and the permanent flow present 95% of the time (Q95). Streamflow regionalization techniques were used to transfer information from the stream gauges to the rest of the basin, so it was possible to compute the relative difference between the estimates (RD%) of all hydrographic segments. The results show that the annual Q95 is 31% higher than the Q7,10, whereas the monthly values were statistically equal. The annual Q7,10 was the most restrictive estimate, however, there is potential to increase from 50% (January) to about 5% (October) when seasonality is considered. Conversely, monthly Q95 can only increase by 20% (February) and has to decrease during dry seasons, i.e. 20% reduction in September, in relation to the annual estimate. The findings show that the consideration of seasonality can optimize water use and, thus, watershed management and planning.