A simulation of biomes on the Tibetan Plateau and their responses to global climate change

The improved process-based equilibrium terrestrial biosphere model (BIOME3China) was run under the present climate to model the potential biomes on the Tibetan Plateau on a 109 grid. The simulated biome was basically in good agreement with a potential natural vegetation map based on a numerical comparison between two maps using the ΔV statistic (ΔV = 0.38). A coupled ocean-atmosphere general circulation model including sulfate aerosols was used to drive a double greenhouse gas scenario to the end of the next century. The simulated vegetation under changed climate with a CO₂ concentration of 500 ppmv and a baseline biome map were also compared using the ΔV statistic (ΔV = 0.4). The climate change would cause a large reduction in the temperate desert, alpine steppe, desert, and ice/polar desert, a large increase in the cold-temperate conifer forest, temperate shrubland/meadow, and temperate steppe, and a general northwestward shift of all vegetation zones. In addition to simulation of biome distribution, BIOME3China also predicted net primary production (NPP) of each grid cell. Comparisons between predicted annual NPP and 160 forest NPP measurements show an agreement between them with a linear regression, despite many problems, such as the quality of the field data. The pattern of predicted annual NPP in the scenario with enhanced CO₂ concentration was the same as that under the present climate; however, the NPP of each biome would increase significantly. Present permafrost simulated using the air frost index was quite similar to the actual frozen ground distribution on the Tibetan Plateau. After the change in climate, the boundary between continuous and discontinuous permafrost would shift toward the north of the plateau by about 1-2° in latitude. The continuous permafrost would mostly disappear, whereas the no-permafrost area would greatly increase. The movement of permafrost would take place with the shift of vegetation zones to the north. The disappearance of permafrost and the expansion of no-permafrost areas would accelerate the desertification of the Tibetan Plateau.