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).