Monday, 15 January 2007
Observations and Influence of Groundwater on Surface Fluxes Using the NOAH Land Suraface Model in the Nebraska Sand Hills
Exhibit Hall C (Henry B. Gonzalez Convention Center)
In this study of the surface water and energy balances of three distinct locations in the Nebraska Sand Hills, special attention is paid to the role of the water table and its influence on the surface layer meteorology. One major limitation of the uncoupled NOAH-Land Surface Model (LSM) is the absence of explicit groundwater representation. Time-variant changes in the depth of subsurface water is an important component of the Sand Hills water cycle and is a crucial entity in providing both reasonable evapotranspiration (ET) values and partitioning of the surface energy fluxes. There has been little research to date focused on land atmosphere interactions where an influx of groundwater, varying in depth during much of the year, affects the surface energy budget. As routine observations of neither soil moisture nor depth to groundwater are readily available for input into numerical models, a simple method to compute additional subsurface water for grid cells containing a high water table is presented. Adjustments were made to the NOAH-LSM depending on site characteristics and annual observed values of soil moisture to account for the influence of the water table in annual model simulations. Comparisons were then made between the modeled and observed soil moisture and surface flux values for each site. It was determined that over the diurnal and annual cycle, there was improved performance by the NOAH-LSM in capturing the evolution of the surface fluxes when compared to unadjusted model simulations for each location.