The Impact of an Open Water Balance Assumption on Understanding the Factors Controlling the Long‐Term Streamflow Components

Abstract

AbstractUnderstanding how streamflow and its components, baseflow and quickflow, vary spatially according to climate and landscape characteristics is fundamental for dealing with different water‐related issues. Analytical formulations have been proposed to investigate their long‐term behavior and additional influencing factors, suggesting that they are mainly controlled by the aridity index (). Nevertheless, these studies assume the catchment as a closed water balance system, neglecting inter‐catchment groundwater flow (IGF). This simplification makes the analysis of the long‐term streamflow components and their main control mechanisms challenging, given that many catchments cannot be considered as closed hydrologic entities. Here, we assessed the controls of the mean‐annual streamflow components and their behavior under an open water balance assumption, using observed data of 734 Brazilian catchments with diverse hydroclimatic conditions. Our results indicate that indeed streamflow components are primarily controlled by at the mean annual timescale. The consideration of an open water‐balance significantly improved the performance of aridity‐based functional forms to describe streamflow components while also elucidating how catchments' attributes may influence streamflow behavior. Land cover, groundwater, climate seasonality, and topographic attributes appeared as the main control mechanisms besides aridity. Overall, our study provides new insights into the main control mechanism of the streamflow behavior at the long‐term scale, while shedding light on the importance of the open water‐balance assumption for model development and water resources management.