Relative impacts of vegetation coverage and leaf area index on climate change in a greener north

To identify relative impacts of vegetation coverage and leaf area index (LAI) on climate in a greener north, a set of climate model sensitivity experiments was conducted in which vegetation coverage and/or LAI were increased over the land poleward of 60 degrees N. The simulation results indicate that an increase in vegetation coverage makes a significant contribution to surface warming, while increasing LAI does not. The increased vegetation coverage reduces both background (snow-free) and snow-covered surface albedos and results in a maximum surface warming (> 2 degrees C) during spring and early summer. The increase in vegetation coverage also alters the partitioning between soil evaporation and vegetation evapotranspiration, and consequently reduces soil moisture loss from surface soil. Increased LAI leads to an enhancement of both convective and large scale components of precipitation, while the increase in vegetation coverage primarily increases the ratio of convective to large-scale precipitation.