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

Abstract

Understanding catchment hydrological responses to rainfall 𝐴𝐴 𝐴𝐴 , represented by the water balance components streamflow 𝐴𝐴 𝐴𝐴 and evapotranspiration 𝐴𝐴 ET , and how they vary with climate and landscape properties is crucial for water-related issues and remains as one of the major challenges in hydrological studies (Gnann et al., 2019;Padrón et al., 2017;Williams et al., 2012). Despite the importance of understanding the relationship between 𝐴𝐴 𝐴𝐴 and catchment's climatic and physiographic properties, additional insight into water balance partitioning can be gained by looking into the decomposition of streamflow in its components (Sivapalan et al., 2011). The two-step water balance proposed by L'vovich (1979), assumes that 𝐴𝐴 𝐴𝐴 may be disaggregated into two primary components: direct runoff 𝐴𝐴 𝐴𝐴𝐷𝐷 and baseflow 𝐴𝐴 𝐴𝐴𝐵𝐵 . The former represents the fast response of a catchment to a rainfall event, while the latter denotes the slow response, representing the water stored in the catchment system (Meira Neto et al., 2020;Price, 2011;Zhang & Schilling, 2006). As a quick response, 𝐴𝐴 𝐴𝐴𝐷𝐷 is usually associated with flood and soil erosion hazards, while 𝐴𝐴 𝐴𝐴𝐵𝐵 is related to water supply and aquifer recharge issues. Accurate knowledge of streamflow components and how they are controlled by climate, land use conditions, and catchments' physiographic characteristics is of primary importance to improve water resources management strategies and to provide additional insights into water balance partitioning, especially in a context of changing climate and increasing water demand (

Brazilian Water Security Threatened by Climate Change and Human Behavior

“…Nevertheless, it is important to highlight that even adopting this simplification in the PET estimation, the A eff -corrected functional forms exhibited a very good performance in characterizing observed long-term water availability Q, being able to explain nearly 87% of its between-catchment variance (see Figure 1). Those values are quite similar with the ones found by Ballarin et al (2022) when using the Priestey-Taylor PET formulation and the same functional forms, suggesting that the r s -simplification does not exert a significant impact on our findings.…”

“…Details about the calibration‐validation procedure, which was conducted using observed catchments' daily streamflow timeseries available in the CABra's data set, can be found in Ballarin et al. (2022). Since we are interested in disentangle climate change impacts on water availability, we assumed here that catchments will follow their Budyko‐based trajectories in the future.…”

“…The functional forms' calibrated parameters for both close (CWB) and open (OWB) water balance assumptions are displayed in Table 1. Details about the calibration-validation procedure, which was conducted using observed catchments' daily streamflow timeseries available in the CABra's data set, can be found in Ballarin et al (2022).…”

“…These functional forms, however, were formulated under the assumption of a CWB, which may not be valid as, in many cases, catchments cannot be considered as closed hydraulic entities (Fan, 2019;Roderick et al, 2014). Hence, we adopted in this study the framework proposed by Ballarin et al (2022), which links the Budyko-based functional forms (Equations 3-5) to the effective area (A eff ) approach, proposed by Liu et al (2020), to account for inter-catchment groundwater exchanges under an open-water balance assumption. Basically, this framework uses an effective area (A eff , Equation 6), rather than the topographic one (A topo ), as the basic spatial unit to compute catchments' hydrological fluxes.…”

Climatic Control on Mean Annual Groundwater Evapotranspiration in a Three‐Stage Precipitation Partitioning Framework

“…Runoff in the one‐stage partitioning framework is separated into fast flow and slow flow in the two‐stage partitioning framework. Both frameworks were originally proposed for natural watersheds with closed water balance; however, they have been extended for watersheds with human activities (Han et al., 2021) and/or open water balance systems (Ballarin et al., 2022).…”