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Abstract:
The BIOME model of Prentice et al. (1992; J. Biogeogr. 19: 117-134), which predicts global
vegetation patterns in equilibrium with climate, was coupled with the ECHAM climate model of the
Max-Planck-Institut fiir Meteorologie, Hamburg, Germany. It was found that incorporation of the
BIOME model into ECHAM, regardless at which frequency, does not enhance the simulated climate
variability, expressed in terms of differences between global vegetation patterns. Strongest changes
are seen only between the initial biome distribution and the biome distribution computed after the first
simulation period, provided that the climate-biome model is started from a biome distribution that
resembles the present-day distribution. After the first simulation period, there is no significant shrinking,
expanding, or shifting of biomes. Likewise, no trend is seen in global averages of land-surface
parameters and climate variables. Significant differences in the results of the climate-biome model are
found when single-year and multl-year climatologies are compared regardless whether climate and
biome model are used in an off-line mode or are interactively integrated. It is concluded that a biome
model should be coupled with a climate model in the following way: firstly, the climate model should
be integrated over several years; secondly, a biome distribution should be computed from the corresponding
multi-year simulated climatology; finally, land-surface parameters are to be deduced from
the biome distribution as boundary condition of the climate model for a subsequent integration, and so
on until an equilibrium is established. Starting the climate-biome model from a biome map which drastically
differs from today's global distribution of biomes, but keeping present-day ocean temperatures
fixed, it takes several iterations until the model finds a new equilibrium differing from the present-day
vegetation distribution in certain parts of the globe. This study indicates that the results of the climatebiome
model are dependent on the initial land-surface conditions.
