The Source Region of the Yellow River (SRYR) is known as the "Water Tower of the Yellow River", which is the most important water conservation area in the upper reaches of the Yellow River. The streamflow of the SRYR makes an important contribution to the water resources in the Yellow River basin. Based on the Weather Research and Forecasting Model Hydrological modeling system (WRF-Hydro) model, by using meteorological, hydrological observations and reanalysis data, the key variables of the

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... led atmosphere-land-hydrological processes over the SRYR during the 2013 rainy season (May-August) are analyzed, and the simulation results of the fully coupled WRF-Hydro with those of the standalone WRF are compared, whose aim is to assess the impact of hydrological coupling on the regional atmospheric model settings. The results show that the WRF-Hydro model has ability to depict the characteristics of streamflow over the SRYR with a Nash Efficiency Coefficient (NSE) of 0.44 during the calibration period from June 1 st , 2012 to September 30 th , 2012 and a NSE of 0.61 during the validation period from May 1 st , 2013 to August 31 st , 2013. Compared with the standalone WRF model, the fully coupled model tends to show better performance with respect to temperature, downward longwave radiation, downward shortwave radiation, latent heat, sensible heat and soil temperature and moisture. Although the wet bias of the coupled simulated precipitation slightly increases (2.51 mm vs. 2.50 mm) due to the consideration of lateral flow of soil water, the simulation results of the land-atmosphere water-heat exchange fluxes and soil heat fluxes are comparably improved. Compared with the observations, the mean Root Mean Square Error (RMSE) of latent and sensible heat is reduced to 32.27 W•m -2 and 24.91 W•m -2 , and of surface soil temperature and moisture is reduced to 4.22 K and 0.06 m 3 /m 3 . Besides, the fully coupled model is able to capture the variation characteristics of streamflow with a NSE of 0.33, which indicates that the fully coupled WRF-Hydro model has great potential for characterizing coupled atmosphere-land-hydrological processes and streamflow simulation in the cold climatical and complex topographic regions. Introduction Water, energy and heat flux and the processes among the atmosphere, land surface and hydrology are closely linked through highly complex interactions (Arnault et al., 2016; Fersch et al., 2020) . In the water cycle of the whole Earth Climate System, the land surface hydrological processes are the link between atmospheric water (e.g. precipitation, evapotranspiration, water