WOFOST_GT introduction

Crop models, like many representations of environmental processes, tend to be over-parameterised. A redesign of the SUCROS family of crop models, largely driven by sensitivity analysis, is presented here. In particular, two new versions of WOFOST, the most widespread model from this family, were developed. The first (WOFOST-GT) reduces model complexity through the definition of functions driven by few parameters with biological meaning.

A portion of the large number of parameters present in SUCROStype models is explained by the high level of detail used to represent biophysical processes, and should be considered as a positive, intrinsic feature of this family of models. Nevertheless, the main reason for the over-parameterization is the presence of AFGEN (Arbitrary Function GENerator) tables to describe the dependence of some parameters on air temperature or development stage. Especially when parameters are calibrated using observations related to just one state variable (e.g., aboveground biomass), AFGEN tables could allowthe user to fit unrealistic functions for the description of plant processes. Therefore, although these functions could potentially lead to a better fit of the outputs during calibration because of their high flexibility, they increase the risks of losing adherence with actual biophysical phenomena.

The methodology used to reduce the complexity of the original version of WOFOST is based on the substitution of the AFGEN tables with functions (i) driven by few parameters with a clear biophysical meaning to simplify parameterization activities, and (ii) able to properly formalize the available knowledge on changes in parameter values according to crop development or air temperature (Stella et al., 2014)

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