Niuetal-07 - Click Here JOURNAL OF GEOPHYSICAL RESEARCH,...

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Development of a simple groundwater model for use in climate models and evaluation with Gravity Recovery and Climate Experiment data Guo-Yue Niu, 1 Zong-Liang Yang, 1 Robert E. Dickinson, 2 Lindsey E. Gulden, 1 and Hua Su 1 Received 17 May 2006; revised 24 October 2006; accepted 26 December 2006; published 7 April 2007. [ 1 ] Groundwater interacts with soil moisture through the exchanges of water between the unsaturated soil and its underlying aquifer under gravity and capillary forces. Despite its importance, groundwater is not explicitly represented in climate models. This paper developed a simple groundwater model (SIMGM) by representing recharge and discharge processes of the water storage in an unconfined aquifer, which is added as a single integration element below the soil of a land surface model. We evaluated the model against the Gravity Recovery and Climate Experiment (GRACE) terrestrial water storage change ( D S ) data. The modeled total water storage (including unsaturated soil water and groundwater) change agrees fairly well with GRACE estimates. The anomaly of the modeled groundwater storage explains most of the GRACE D S anomaly in most river basins where the water storage is not affected by snow water or frozen soil. For this reason, the anomaly of the modeled water table depth agrees well with that converted from the GRACE D S in most of the river basins. We also investigated the impacts of groundwater dynamics on soil moisture and evapotranspiration through the comparison of SIMGM to an additional model run using gravitational free drainage (FD) as the model’s lower boundary condition. SIMGM produced much wetter soil profiles globally and up to 16% more annual evapotranspiration than FD, most obviously in arid-to-wet transition regions. Citation: Niu, G.-Y., Z.-L. Yang, R. E. Dickinson, L. E. Gulden, and H. Su (2007), Development of a simple groundwater model for use in climate models and evaluation with Gravity Recovery and Climate Experiment data, J. Geophys. Res. , 112 , D07103, doi:10.1029/2006JD007522. 1. Introduction [ 2 ] Groundwater storage constitutes about 30% of the global freshwater storage. This is a large percentage when compared with the amount of water stored in soil, wetlands, and permafrost, all of which constitute only 1% of the global freshwater. Groundwater interacts with soil, vegetation, and climate. Groundwater storage shows as large variations as that of soil water at monthly or longer timescales in Illinois [ Rodell and Famiglietti , 2001]. The groundwater level also shows a strong diurnal cycle in aquifers where the water table depth is less than 2 m because of the water uptake by the roots of the above- ground plants [ Fan et al. , 2007]. Groundwater influences soil moisture and hence surface energy and water balances in regions where the water table is shallow [ Gutowski et al. , 2002; York et al. , 2002; Liang et al. , 2003; Chen and Hu , 2004; Yeh and Eltahir , 2005]. The rise and fall of the water table directly interacts with soil moisture in
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This note was uploaded on 11/07/2011 for the course EAS 8803 taught by Professor Staff during the Spring '08 term at Georgia Institute of Technology.

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Niuetal-07 - Click Here JOURNAL OF GEOPHYSICAL RESEARCH,...

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