Development of a Simple Groundwater Model for Use in Climate Models and Evaluation with Gravity and Climate Experiment Data

Guo-Yue Niu, Zong-Liang Yang, Robert E. Dickinson, Lindsey E. Gulden, and Hua Su, Journal of Geophysical Research, Vol. 112, D07103, doi:10.1029/2006JD007522, 2007

Motivations

• Develop a simple groundwater model (SIMGM) to represent groundwater dynamics in GCMs

• Evaluate SIMGM against observations to see whether this model is realistic

• Compare the updated model to the previous model to investigate the impact of this modification on the simulation of soil moisture and evapotranspiration

Background

Background

• Recent study shows that surface runoff is an exponential function of water table depth.

• TOPMODEL-based runoff scheme formulates the base flow as an exponential function of water table depth.

• Deficiencies of current land surface models

• Several methods to improve the model

Model Descriptions

• Add an unconfined aquifer to an LSM’s soil column

• Apply a simple TOPMODEL-based runoff scheme:

Model Descriptions

• Represent groundwater recharge and discharge processes

• Update the gravitational drainage with the groundwater recharge as the lower-boundary condition

• The water table depth is converted from the aquifer water storage scaled by the specific yield (0.2)

Evaluation against GRDC Runoff Product

Evaluation against GRDC Runoff Product

Evaluation with GRACE

Evaluation with GRACE

Relationship of P – E with Recharge & Discharge

Comparison to FD

Comparison to FD

Comparison to FD

Conclusions• SIMGM was developed to represent groundwater dynamics in

GCMs.

• Global runoff produced by SIMGM agrees well with the GRDC runoff.

• Both modeled total water storage and water table depth anomalies are in good agreement with those from GRACE,

• Discharge, recharge, soil water and water table depth are controlled by P-E.

• SIMGM produced much more soil moisture and 4% - 16% more annual ET than FD.

Discussions

• Integration elements

• Is aquifer connected to the bottom layer of the soil column?

• Specific yield?

• Initialization of the model