Extrapolation of equations in low flow regionalization: Alternatives to mitigate the risks

Abstract

Streamflow regionalization is an important tool for estimating the streamflows along the hydrography, however, extrapolation of regionalization equations is not recommended beyond the limits of the sample data. This study aimed to present alternatives to minimize risks associated with the extrapolation of regionalization equations for low flows. The study was conducted for Pará river basin. The performance of new explanatory variables was evaluated for Q_7,10 regionalization. The physical characteristic used was the drainage area. The climatic variables considered were the rainfall converted into the equivalent streamflow (P_eq) and rainfall minus an abstraction value, which is 750mm (P_eq750). It’s also presented an imposition of a low flow threshold specific to impose a restriction for low flows in extrapolation regions. The use of P_eq to replace area as explanatory variable, and P_eq750 instead of this one, promoted significant differences in statistics of adjustment equations and as well as in behavior of Q_7,10. The use of a threshold value of physical imposition was an important possibility to extend the use of regionalization equations along hydrography sections where the use of these equations was not recommended.