Precipitation response to land subsurface hydrologic processes in atmospheric general circulation model simulations

Several studies have established that soil moisture increases after adding a groundwater component in land surface models, owing to the additional supply of subsurface water. However, the impact of groundwater on the spatial-temporal variability of precipitation has received little attention. This study explores how a groundwater representation in land surface models alters precipitation distributions through coupled groundwater-land-atmosphere simulations. Results indicate that the addition of groundwater yields a global increase in soil water content and evapotranspiration, a decrease in surface air temperature, and an increase in cloud cover fraction. These result in globally inhomogeneous changes in precipitation. In the boreal summer, tropical land regions show a positive anomaly in the Northern Hemisphere and a negative anomaly in the Southern Hemisphere. As a result, an asymmetric dipole is found over tropical land regions along the equator. Furthermore, in the transition climatic zone where the land and atmosphere are strongly coupled, precipitation also increases. Two main mechanisms are suggested for the two different regions with increased precipitation. The "rich-get-richer" mechanism is responsible for the positive precipitation anomalies over the tropical land regions, while a positive feedback of land-atmosphere interaction is the major contributor to increased precipitation over central North America. This study highlights the importance of land subsurface hydrologic processes in the climate system and has further implications for global water cycle dynamics.