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• The impact of satellite actual evapotranspiration assimilation on runoff simulations is assessed for 149 CAMELS basins. • The assimilation of GLEAM, REA-ET, and GLDAS ETa products shows relatively small improvements in runoff simulations. • The data assimilation using GLEAM ETa data yielded the best performance in runoff simulations. • The influence of multiple catchment characteristics is evaluated for the runoff simulation. Data assimilation (DA) techniques that integrate remotely sensed observations and in-situ measurements into hydrological models have been extensively implemented, but few studies have applied multisource actual evapotranspiration (ETa) products to evaluate its impacts on the DA performances through a large number of basins with different catchment conditions. This study performs a DA experiment to assess the influence of remotely sensed ETa products on streamflow simulations over 149 Catchment Attributes and Meteorology for Large-sample Studies basins across the contiguous United States, and the relationships between the DA results and multiple catchment characteristics are further analyzed. In this experiment, three satellite ETa products from the GLEAM, REA-ET, and GLDAS are assimilated into a conceptual rainfall-runoff model (i.e., HYMOD) using the ensemble Kalman filter. The results show that assimilating the three ETa products provides relatively small improvements compared to the open loop (OL) scenario in approximately 48%-58% of the study basins, and around 14%-19% of these basins exhibit an increase in Nash-Sutcliffe Efficiency over 0.01. Specifically, the GLEAM ETa shows the greatest improvements in runoff, followed by the GLDAS and REA-ET products. The OL performance plays a significant role in runoff improvements, greater improvements are achieved for basins with poor OL runoff simulations. The assimilation efficiency is revealed to be relevant to the accuracy of the satellite ETa products. While the catchment conditions such as the aridity index, mean slope, the fraction of forest, and catchment area are found to have a limited effect on the spatial pattern of ET assimilation performances. [ABSTRACT FROM AUTHOR]

• A monthly hydrological model is developed based on the proportionality hypothesis. • The TSPM model achieves satisfactory runoff simulations, especially in high flow. • The climatic characteristic plays pivotal role in model performance, as well as the forest fraction. Monthly hydrological models are very useful tools for modeling of catchment hydrology. In this study, a two-stage partitioning monthly water balance model (TSPM) with three parameters is developed based on a generalized proportionality hypothesis. A total of four model scenarios are conducted to investigate the effects of calculation procedures of the soil water content on model performances by incorporating the hyperbolic tangent function used in the two-parameter monthly water balance model (TWBM) by Xiong and Guo (1999). The developed monthly models are then tested in 205 Catchment Attributes and Meteorology for Large-sample Studies (CAMELS) basins across the United States. Application results demonstrate that the three-parameter model TSPM1 performs well and has better performance than the modified two-parameter model TSPM4 using the equations of soil moisture and runoff from the TWBM. Five monthly models with different structures and model parameter numbers are compared to the two developed TSPM models. Results show that the TSPM1 and TSPM4 models have a median performance among these models. They show an excellent performance in high flow, but a relatively weak performance in low flow, especially for the TSPM4 model. The relationship between the model performances and catchment characteristics is explored and results demonstrate that the climate and vegetation conditions of catchment (e.g., aridity index and forest fraction) exert very significant effects on model performances, including entire goodness-of-fit, low and high flows in runoff simulations. [ABSTRACT FROM AUTHOR]