Vegetation root distribution is an important factor in determining the rates of water extraction from different soil layers. Using a comprehensive observational global root database, the vertical root distribution and rooting depth have been changed in the Land Surface Model(LSM) coupled with the NCAR Community Climate Model(CCM).

Accurate representation of vegetated surfaces is vital to the distribution of surface energy and water balances in a climate modeling system. Fractional vegetation cover and leaf area index(LAI) have been derived at 8km resolution from normalized difference vegetation index. These data provide accurate estimation of seasonal LAI variation and fractional vegetation cover for each LSM vegetation type. The data were used to adjust the existing LSM vegetation parameters.

Results of the global CCM/LSM model will be presented from seasonal ensemble simulations of 1988 and 1993. The simulations provide evidence of the impacts of vegetation root distribution, fractional vegetation cover, and LAI on warm season precipitation over the contiguous United States.