Impact of observed vegetation root distribution on seasonal global simulations of land surface processes

Using a global root distribution derived from observations, results from June to August ensemble simulations are presented. The new root distribution shifts the location of roots in the soil in most regions of the world. Root relocation depends on land use type with some roots located shallower (e.g., grasslands) and others deeper (e.g., tropical forests). Comparison of the boreal summer results of 1988 and 1993 for a control simulation and simulation with the new root distribution produces, in several regions of the world, statistically significant differences of up to 40 W/m² in the components of the surface energy budget. Analysis of the eastern and western United States shows statistically significant changes of over 1 K in surface air temperature and over 25 W/m² in surface energy components for both seasonal averages and diurnal cycles. Comparison with observations shows that the new root distribution improves the surface air temperature simulation, especially in 1993, but any precipitation improvement is statistically insignificant.