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

Min-Hui Lo,James S Famiglietti

doi:10.1029/2010jd015134

Abstract

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.

Highlights

Introduction andBackground[2] Unlike the ocean, which has an infinite water supply, the supply of moisture on land is limited and highly variable
This study explores how a groundwater representation in land surface models alters precipitation distributions through coupled groundwater‐land‐atmosphere simulations
After adding a groundwater component in the model, the model produces more precipitation over land owing to an increase in lower tropospheric integrated water vapor (Figure 2d) from an overall increase in top soil water (Figure 2c) and evapotranspiration (Figure 2b)

Summary

Introduction and Background

[2] Unlike the ocean, which has an infinite water supply, the supply of moisture on land is limited and highly variable. [5] Recently, the representation of groundwater dynamics in LSMs has begun to receive considerable attention [e.g., Famiglietti and Wood, 1991, 1994; Liang et al, 2003; Maxwell and Miller, 2005; Yeh and Eltahir, 2005a, 2005b; Fan et al, 2007; Maxwell et al, 2007; Miguez‐Macho et al, 2007, 2008; Niu et al, 2007; Lo et al, 2008] These studies have shown the importance of representing shallow groundwater and its interaction with soil moisture in land hydrologic simulations. In order to remove the effects of uncertain initial and boundary conditions, the 1870–1899 period is treated as spin‐up, and 100 year (1900–1999) simulations are used in the analysis

Results

Discussion

Conclusions