A MODEL ANALYSIS OF THE TERRESTRIAL VEGETATION MODEL OF IMAGE-2.0 FORCOSTA-RICA

The Terrestrial Vegetation Model (TVM) of the Integrated Model to Asse ss the Greenhouse Effect (IMAGE 2.0) determines potential land cover f or natural ecosystems and potential productivity for agrosystems. A mo del analysis of this TVM using Monte Carlo simulations is described fo r the eighteen Costa Rican (0.5 degrees x 0.5 degrees latitude-longitu de) IMAGE 2.0 grid cells. It is demonstrated that the TVM is not overl y sensitive to climate input variability. Much observed output variabi lity is related to model parameters. These model parameter related eff ects can strongly determine the intra/inter grid variability for Costa Rican potential yields. The model analysis indicates that more model refinement is required to make any effort to improve data quality effe ctive. It is therefore proposed to remove as many model criteria as po ssible or to replace them by more gradual criteria based on crop ecoph ysiological characteristics. A first tentative comparison of maize, ri ce and pulses yield potentials and their distribution in Costa Rica du ring 1973 and 1984, suggests that the assumption that the two an relat ed, as assumed in the Land Cover Model (LCM) in IMAGE 2.0, has some va lidity.