Evaluation of the utility of satellite-based vegetation leaf area index data for climate simulations

In this study the utility of satellite-based leaf area index (LAI) data in improving the simulation of nearsurface climate with the NCAR Community Cli mate Model, version 3 (CCM3), GCM is evaluated. The use of mean LAI values, obtained from the Advanced Very High Resolution Radiometer Pathfinder data for the 1980s, leads to notable warming and decreased precipitation over l arge parts of the Northern Hemisphere lands during the boreal summer. Such warming and decreased rainfall reduces discrepancies between the simulated and observed near-surface temperature and precipitation fields. The impact of interannual vegetation extremes observed during the 1980s on near-surfac e climate is also investigated by utilizing the maximum and minimum LAI val ues from the 10-yr LAI record. Surface energy budget analysis indicates tha t the dominant impact of interannual LAI variations is modification of the partitioning of net radiant energy between latent and sensible heat fluxes brought about through changes in the proportion of energy absorbed by the v egetation canopy and the underlying ground and not from surface albedo chan ges. The enhanced latent heat activity in the greener scenario leads to an annual cooling of the earth land surface of about 0.3 degreesC, accompanied by an increase in precipitation of 0.04 mm day(-1). The tropical evergreen forests and temperate grasslands contribute most to this cooling and incre ased rainfall. These results illustrate the importance and utility of satel lite-based vegetation LAI data in simulations of near-surface climate varia bility.