Global climate modeling requires an effective use of physically-based computer parameterizations and accurate and consistent initial conditions for both the atmosphere and land surface. An accurate representation and initialization of vegetated surfaces is vital to the distribution and balance of surface energy and water in a climate modeling system. Fractional vegetation cover and leaf area index(LAI) have been derived at 8km and 1km resolution from normalized difference vegetation index. These data provide an accurate estimation of seasonally varying LAI and annually constant fractional vegetation cover for each CLM vegetation type. Using these data, the existing CLM vegetation parameters have been changed in the Community Land Model (CLM version 2) coupled with the NCAR Community Atmospheric Model (CAM version 2).

Results of the global CAM2/CLM2 model will be presented from seasonal ensemble simulations. The simulations provide evidence of the impacts that fractional vegetation cover and LAI have on warm season precipitation and the partitioning of water resources above and below the soil interface within the contiguous United States. The results will also examine the appropriate number of vegetation types necessary in each model grid to effect the simulation results.