Simulated Water Table and Soil Moisture Climatology Over North America

Abstract

We demonstrate the link between two terrestrial water reservoirs: the root-zone soil moisture and the groundwater, and contribute our simulated climatologic water table depth and soil moisture fields over North America to the community. Because soil moisture strongly influences land?atmosphere fluxes, its link to the groundwater may affect the spatiotemporal variability of these fluxes. Here we simulate the climatologic water table depth at 30-arc-s resolution as constrained by U.S. Geological Survey site observations. Then, we use this water table climatology as the lower boundary for the soil, and variable infiltration capacity (VIC)-simulated land surface flux climatology as the upper boundary, to calculate the soil moisture climatology (SMC) at 14 depths (down to 4 m). Comparisons with VIC, the North America Regional Reanalysis (NARR), and observations suggest the following: first, SMC is wetter than VIC, despite their having identical land surface flux; second, while climate is the dominant signature in NARR and VIC, the water table manifests itself in SMC, with wet soil over the shallow water table; third, while soils in VIC and NARR get drier with depth, soils in SMC get wetter in regions of a shallow water table; and last, SMC has the highest root-zone (top 2 m) total soil water storage. These differences may have implications for climate modeling. We make our simulation results available to any interested researcher, for applications such as model initialization and intercomparison.