GLOBAL VEGETATION CHANGE PREDICTED BY THE MODIFIED BUDYKO MODEL

A modified Budyko global vegetation model is used to predict changes i n global vegetation patterns resulting from climate change (CO2 doubli ng). Vegetation patterns are predicted using a model based on a drynes s index and potential evaporation determined by solving radiation bala nce equations. Climate change scenarios are derived from predictions f rom four General Circulation Models (GCM's) of the atmosphere (GFDL, G ISS, OSU, and UKMO). Global vegetation maps after climate change are c ompared to the current climate vegetation map using the kappa statisti c for judging agreement, as well as by calculating area statistics. Al l four GCM scenarios show similar trends in vegetation shifts and in a reas that remain stable, although the UKMO scenario predicts greater w arming than the others. Climate change maps produced by all four GCM s cenarios show good agreement with the current climate vegetation map f or the globe as a whole, although over half of the vegetation classes show only poor to fair agreement. The most stable areas are Desert and Ice/Polar Desert. Because most of the predicted warming is concentrat ed in the Boreal and Temperate zones, vegetation there is predicted to undergo the greatest change. Specifically, all Boreal vegetation clas ses are predicted to shrink. The interrelated classes of Tundra, Taiga , and Temperate Forest are predicted to replace much of their poleward mostly northern) neighbors. Most vegetation classes in the Subtropics and Tropics are predicted to expand. Any shift in the Tropics favorin g either Forest over Savanna, or vice versa, will be determined by the magnitude of the increased precipitation accompanying global warming. Although the model predicts equilibrium conditions to which many plan t species cannot adjust (through migration or microevolution) in the 5 0-100 y needed for CO2 doubling, it is nevertheless not clear if proje cted global warming will result in drastic or benign vegetation change .