General circulation models (GCMs) are briefly described together with the
parametrizations employed. Aspects especially relevant to changes in vegetation
are emphasized. Factors such as surface albedo, ground hydrological processes,
and aerodynamic surface roughness, which are affected by these changes, are
considered in relation to their contribution to the sensitivity of the models.
Results are summarized for experiments on both global and regional scales,
simulating changes of surface albedo and surface water availability.
A removal of vegetation tends to increase albedo and reduce roughness and
affects surface moisture availability by changing interception, runoff, and the
depth of soil accessible to the roots. Increases in surface albedo decrease
evaporation and also tend to reduce atmospheric moisture convergence and
precipitation. Decreases in surface moisture availability reduce evaporation,
and this generally leads to a decrease of rainfall, which helps to maintain the
surface moisture anomaly. A decrease in surface roughness also affects the
partitioning of upward energy flux between the sensible and latent (evaporation)
forms, with evaporation increasing as roughness decreases for large stomata!
resistances and decreasing for