Influence of the seasonality of stream flows on water use rights criteria: a case study of the Paraopeba river basin

Brazil has one of the most modern laws of water resource management in the world. Among its management and planning tools, the granting of water use rights allows water resource management agencies to control water usage both quantitatively and qualitatively. Given the importance of the granting of water use rights as an instrument of water usage control, this paper sought to analyze the criteria used to grant water use rights considering the influence of the seasonality of yearly stream flows, with the objective of establishing a technical, scientific basis for decision-making by water resource management agencies. The quantitative effects of adopting four-month and six-month seasonal period criteria were analyzed in comparison to the annual periods of stream flow references Q7,10, Q90, and Q95 in order to quantify the relative differences in water availability between the stream flow references adopted for water use rights purposes. In the analysis of Q7,10, the results showed that applying seasonal criteria may increase the amount of water available for water use grants in the periods of higher water availability by up to 126%. Meanwhile, stream flows associated to the permanence of 90% (Q90) and 95% (Q95) showed increases of up to 99% during the rainy period. During the dry period, however, water availability decreased by up to 24.5% in comparison with the annual period criteria calculation base period. Results showed that stream flow analysis based on seasonal criteria provides more flexibility of water availability for water use grants during certain periods of the year.