## 1 Introduction
WRF-Hydro realizes the effective scale conversion of hydrology and land surface modules, solves the problem of resolution mismatch between a climate model and a hydrologic model [22], and reflects the lateral movement of soil moisture and the interaction between surface water and subsurface water. The interrelationship promotes the expression of the land surface hydrological process, and the fully coupled WRF/WRF-Hydro is expected to be able to provide feedback and improve the simulations of the WRF model [23; 24]. Variables that feedback to each other in the fully coupled WRF/WRF-Hydro include soil moisture, land flues of energy, etc. The coupled WRF/WRF-Hydro system has been applied for studies in a number of places in the world. [PERSON] et al. [25] conducted a three-year continuous simulation in southern Italy. The results show that the WRF/WRF-Hydro coupling model produced higher soil moisture content and lower overall surface runoff than WRF-only. [PERSON] et al. [26] investigated the exchange processes between the atmosphere and the land surface using the fully coupled system, by carrying out a comparison experiment from 2004 to 2013 in northwestern Mexico. The results indicated that the soil moisture and vegetation types could affect the convective rainfall, and the initial land surface conditions (such as the soil water storage) were critical for enhancing the simulations. [PERSON] et al. [6] explored the simulation with the coupled WRF/WRF-Hydro in a watershed of East Africa from 2011 to 2014, and showed that the precipitation of the coupled system had little variation compared to WRF and might be affected by the moisture advection outside the domain. Both of the above three fully coupled cases focused on the long-term series of simulation. [PERSON] et al. [27] gave an analysis of a 3-day extreme event in arid region of United Arab Emirates, and the simulated precipitation suggested reducing root mean square error (RMSE) and relative error (RE) trends in the fully coupled WRF/WRF-Hydro than WRF-only. These previous studies show that atmospheric hydrological coupling models have a significant effect on the simulated atmospheric-terrestrial water balance. However, for the discussion of fully coupled WRF/WRF-Hydro, most of the coupling simulations focus on a long time scale, there were not enough cases and few systematic analyses of storm events with different temporal and spatial consistency and the related changes of water cycle elements in the hydrological processes. In semi-humid areas of northern China, there is frequent convectional rain and the runoff generation is mixed with infiltration-excess and storage-excess mechanisms. The rain storm events in such areas, featured with high rainfall intensities, pre-dry soil conditions, and inhomogeneous spatiotemporal distributions, need further simulation accuracy of the terrestrial hydrological processes. This study we explored three basic questions:  
* What are the different spatiotemporal storm simulation performances between WRF-only and the fully coupled WRF/WRF-Hydro in the semi-humid areas of northern China? * Could the fully coupled system improve the precipitation spatiotemporal distribution? * What are the differences in the variation of water cycle elements (e.g., rainfall and soil moisture) of different storm events? To answer the problems above, the WRF-only and coupled WRF-Hydro models were applied to two catchments for six 24-hour rainstorm events with different spatiotemporal homogeneousness of the rainfall distribution. The impact of the enhanced description of atmospheric-terrestrial water balance in WRF-Hydro was investigated by comparing WRF-Hydro and WRF-only results with observations over the region. In order to further understand the simulation results, several crucial water cycle elements, i.e., the generated runoff, the evapotranspiration, and the soil moisture were also analyzed and compared between the fully coupled modeling system and the stand-alone WRF model.