Observations and influence of groundwater on surface fluxes using the NOAH land surface model in the Nebraska Sand Hills

The NOAH-LSM was modified to include the influence of subsurface water at two inter-dune regions in the Nebraska Sand Hills where the water table is near the surface. Mean monthly depths to subsurface water were used with a weighting function to adjust the soil moisture at the lowest model soil level. The effect of this additional soil water on ET and the surface fluxes were examined. The NOAH-LSM overestimated the annual ET and latent heat flux while underestimated the sensible heat flux at the dry valley site, where the groundwater is likey less an influence on the upper soil moisture. At the wet valley site, the addition of subsurface water improved the diurnal and annual estimation of ET. This in turn improved the partitioning of the latent and sensible heat fluxes to better represent the observed values. In the absense of a more sophisticated hydrologic model coupled to the NOAH-LSM, this simple yet effective method of accounting for the influence of subsurface water on soil moisture can be used with good accuracy if reliable data on depth to subsurface water are available.