Impact of Lateral Terrestrial Water Flow on Land-Atmosphere Interactions in the Heihe River Basin in China: Fully Coupled Modeling and Precipitation Recycling Analysis

Lateral terrestrial water flow is usually not considered in regional climate modeling. This study focuses on the impact of increased hydrological model complexity for the description of the land-atmosphere interactions in a complex terrain region. For this purpose, we apply the Weather Research and Forecasting (WRF) model with its hydrological modeling extension package WRF-Hydro for the case of the Heihe River Basin in convection permitting atmospheric resolution (3 km). The Heihe River Basin (143,200 km(2)) is an arid-semiarid inland river basin in Northwestern China. By comparing model simulations results with and without coupling for the period 2008-2010, the effect of lateral terrestrial water flow on land-atmosphere interactions is evaluated 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 temperature and precipitation variability similar to the 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 excess 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 affects 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 our study area.