## 4 Discussion  
Enhanced hydrological representations on short-term meteorological forecasts are more uncertain, and as yet under investigation and understanding its impact [25]. The concept of coupling the hydrological model (WRF-Hydro) with atmospheric model (WRF) was expected to reduce uncertainties associated with the spatial and temporal distribution of storm events, especially for complex terrain. In this study, six storm events were screened with different spatiotemporal characteristics during a 24-hour window. The focus is to explore the short-term temporal and spatial water exchanges of elements in the water cycle, especially different spatiotemporal types rainfall between WRF-only and the coupled WRF/WRF-hydro in the semi-humid areas of northern China, where the short real rainfall duration is regarded as a great challenge to the coupled system. Through categorical and continuous indices, we proved a potential for the fully coupled system to reduce spatial mean square error and could be confirmed from the enhancement spatial distribution of precipitation in the fully coupled WRF-Hydro, especially for the simulation of rainstorm centers. However, when the fully coupled WRF/WRF-Hydro is used, attention should be paid to the false alarm risk of rainfall occurrences and period rainfall values in time inhomogeneous storms which have large rainfall intensity. The distribution of precipitation among land water cycle elements is a complex process, and more details are not yet fully explored [54]. In our study, the redistributions fluctuation of spatial precipitation in the fully coupled system was highly correlated with soil moisture, and a low initial soil moisture corresponded to a large spatial fluctuated range. The feedback process of the increased soil moisture after the spatial redistribution led to the increase in precipitation in the corresponding position, indicating that there may be a positive feedback relationship between local soil moisture and precipitation. The spatial redistribution of soil moisture will change the surface flux, which may  
Figure 14: Spatial distributions of the 24 h cumulative evapotranspiration: (**a**) WRF-only; (**b**) the fully coupled WRF/WRF-Hydro. affect boundary layer dynamics, the initiation of moist convection and precipitation [55; 56]. In this study, the fully coupled system generally produced higher soil moisture content than WRF-only. This was consistent with the previous study by [PERSON] et al. [25], which claimed before that the reason was related to the combined effects of lateral terrestrial water flow redistribution in the fully coupled system by allowing more water to circulate in the regional water cycle. The fully coupled system is unstable and far from maturity [57]. After a disaggregation of the land surface module, the coupled WRF-Hydro carries out the overland and undersurface routing on a finer grid, and then, through average of the subgrid, aggregates and feeds back to the LSM to realize the horizontal interaction between the hydrological module and LSM. It solves the spatial variability structure of soil moisture resolution from one to the next time step. One of the model structure restraints is that even if there are adjustable thicknesses of four soil layers in WRF-Hydro, they are constant throughout the entire model domain. This does not bring much trouble to this study due to the relatively single local soil type (cinnamon soil), but for the areas with strong soil heterogeneity, it is still a problem to be solved because the main runoff generation processes are carried out in the 'fixed column'. Since the primary objective of the study is to show the effects of different spatiotemporal types rainfall between WRF-only and the fully coupled WRF/WRF-Hydro in the semi-humid areas of northern China, rather than extensively assessing the performance of the hydrological module, the streamflow is limited to only a simple foregoing calibration of four sensitivity parameters in the stand-alone WRF-Hydro.