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. © 2008 American Meteorological Society.