Open Access

Zhenyu Zhang

• Regional climate modeling integrating the water, energy and mass exchange at and between the subsurface, land surface and atmosphere provides a useful tool to inves- tigate the regional water cycle and land-atmosphere interactions. Current regional climate modeling frameworks focus on the description of sophisticated terrestrial hy- drological processes, such as lateral terrestrial water flow. However, the effect of the complexity of terrestrial hydrological processes to atmospheric modeling is not fully understood in all its details yet. This dissertation contributes to the improved under- standing of the joint terrestrial and atmospheric water balance and land-atmosphere interactions in mountainous areas. The application region is the Heihe River basin (HRB), an endorheic basin located in northwest China, which is characterized with complex terrain and heterogeneous natural features. The human activities in this area suffer from water-stress related issues, which requires the properRegional climate modeling integrating the water, energy and mass exchange at and between the subsurface, land surface and atmosphere provides a useful tool to inves- tigate the regional water cycle and land-atmosphere interactions. Current regional climate modeling frameworks focus on the description of sophisticated terrestrial hy- drological processes, such as lateral terrestrial water flow. However, the effect of the complexity of terrestrial hydrological processes to atmospheric modeling is not fully understood in all its details yet. This dissertation contributes to the improved under- standing of the joint terrestrial and atmospheric water balance and land-atmosphere interactions in mountainous areas. The application region is the Heihe River basin (HRB), an endorheic basin located in northwest China, which is characterized with complex terrain and heterogeneous natural features. The human activities in this area suffer from water-stress related issues, which requires the proper knowledge of the regional water balance. For this purpose, the Weather Research and Forecasting (WRF) model and its hydrologi- cal modeling extension package WRF-Hydro are applied for the case of the HRB. The atmospheric modeling is configured at convection permitting scale 3 km, and the additional lateral terrestrial water processes with WRF-Hydro are resolved at 300 m fine hydrological sub-grid. The effect of lateral terrestrial water flow on re- gional climate modeling is investigated by comparing the model simulations results with and without this hydrological extension coupling for the period 2008-2010, and is quantified with a joint atmospheric-terrestrial water budget analysis, a regional precipitation recycling analysis and a fully three-dimensional atmospheric moisture tracing method (evaporation tagging). The coupled modeling system WRF-Hydro simulates near-surface hydrometeorological variability similar to the standard WRF model and demonstrates, in addition, its ability to reproduce daily streamflow. In the fully coupled mode, as a consequence of lateral terrestrial water flow description, the redistribution of infiltration excesses in the mountainous area produces higher soil moisture content in the root zone, increases the terrestrial water storage and evapotranspiration and decreases the total runoff. The resulting wetting and cooling in the near-surface affect the regional climate by changing the regional water vapor transports and water vapor content, while, in turn, inducing precipitation differences. Overall, the fully coupled modeling increases the recycling rate, indicating that lateral terrestrial water flow influences regional climate in the study area.…