River discharge is a crucial indicator to understand terrestrial water cycles and supplies necessary information about water resource management (Adnan et al., 2020). Direct measurement of river discharge, such as employing the acoustic Doppler current profiler, is complicated, costly, time-consuming, and labor-intensive because it requires a number of current sensors and repeated surveys performed by boats and is thus unsafe under unfavorable flow and weather conditions (Gisen & Savenije, 2015;Matte et al., 2018). Other noncontact methods, including large-scale particle image velocimetry (LSPIV) (Akbarpour et al., 2020) and remote sensing (Kebede et al., 2020), have recently begun to be used for discharge measurements. Nevertheless, the use of these methods in contiguous monitoring of river discharge is not feasible; for example, LSPIV cannot measure discharge in large rivers because of limited camera coverage, while satellite images are not always available due to cloud cover, particularly during rainy seasons. As a result, at hydrological stations situated on rivers worldwide, flow discharge is not directly measured; rather, it is indirectly estimated either from the widely used stage-discharge rating curve (RC) method or from cubature, rating-fall, tide-correction, and coaxial graphical-correction methods (Matte et al., 2018), in which the stage (water level) is recorded at specific intervals (e.g., daily, hourly, or sub-daily) depending on the goal of the measurements. Due to technical, financial, maintenance and political instability issues, long-term flow discharge datasets may have gaps, resulting in the loss of information or the misinterpretation of historical flow regime changes and hydrological processes (Tencaliec et al., 2015). Therefore, it is important to reconstruct missing discharge values to reliably provide helpful information for water resource management at the basin scale.Several methods, including statistical methods, numerical models, and machine learning (ML) algorithms, have been employed to predict river flows. Recently, ML techniques, such as support vector regression (SVR) (Adnan et al., 2020;Luo et al., 2019), random forest (RF), Gaussian process regression (GPR) (Sun et al., 2014), M5