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close this bookForests, Climate, and Hydrology: Regional Impacts (UNU, 1988, 217 pages)
close this folder8. Review of general circulation models as a basis for predicting the effects of vegetation change on climate
View the document(introductory text...)
View the documentAbstract
View the documentIntroduction
View the documentGeneral circulation models
View the documentResponse to variation in land surface properties
View the documentGCM Simulations of tropical rainfall
View the documentRecommendations for future research
View the documentSymbols and abbreviations
View the documentReferences
View the documentAssessment


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 small.