Development and Validation of a Three‐Dimensional Variably Saturated Flow Model for Future Water Resource Assessment at a Global Scale—Targeting Saturated Groundwater Flow in Plains

Abstract A three‐dimensional variably saturated flow model was developed for assessing future global water resources and parameterized groundwater pumping. We applied this to an actual watershed verify its validity as Earth System Model. For applicability, the parameterization method multi‐layered pumping verified through comparison with observations MODFLOW results. The proposed in study is applicable even when multiple wells are present within one horizontal computational grid well spans vertical grids. This can be at scale without parameters such radius, which data may difficult obtain. recreated seasonal annual variations observed values. Furthermore, results were comparable those of MODFLOW. However, calculation overestimated relative overestimation likely due active Central Valley before start unsteady‐state calculation. Therefore, level beginning calculated using values, improving reproducibility. levels unlikely available scale, steady‐state calculations conducted over 15 60 years considering not reproducible obtained levels. These suggest that set important global‐scale