Comparison of the Fraction Absorbed Photosynthetically Active Radiation (FPAR) data derived from AVHRR NDVI data with that estimated by the LPJ global dynamic vegetation model, for the period July 1981-June 1998

Global models are increasingly being used to investigate global dynamic processes. A key issue with any modelling is to be able to assess how closely the models replicate real conditions, before those models can be used for predicting future conditions. With temporal models this evaluation is very difficult. This paper describes four techniques that have been developed to assist in comparing temporal image data of actual conditions with those predicted by a model. In this case FPAR data derived from AVHRR data have been compared with FPAR values computed by the LPJ model of global vegetation dynamics. The paper reviews the main findings that have come out of this comparison at this date.