2.1.2 Groundwater lateral flow (GLF)
A two-dimensional groundwater (GW) movement equation based on Darcy’s
Law and the Dupuit approximation (Bear 1972) was used to realize GW
exchange between grid cells. The numerical formulation of this equation
considered the equal chance of a cell exchanging water with its
horizontal neighboring cells from eight directions. The GLF module was
calculated in a 1-km-sized cell based on the water table gradients
between itself and its neighboring cells, which then updated the
groundwater table depths based on both the GLF fluxes and the vertical
water flux obtained from CAS-LSM, and the calculated lateral flux was
sent back to CAS-LSM to adjust the water table at the coarse land model
resolution. A simple resolution conversion method based on the LSM
sub-grid structure was used to link CLM4.5 and the GLF module at
different resolutions. For the depth-to-bedrock that describes the
distance between the ground surface and the less permeable bedrock
layers, we used the global data set of depths-to-bedrock at 1-km
resolution presented by Shangguan et al. (2017).