NON-DIMENSIONALISATION OF THE PENMAN-MONTEITH MODEL

The Penman-Monteith model is expressed in non-dimensional form. Scalings are selected such that the groups of dimensionless variables lie between minus one and plus one. The relative importance of each term in the equation is assessed from the size of the dimensionless parameters. In extreme cases where very large or very small values are found, asymptotic analysis allows equation simplification. Hourly field data from savannah vegetation and pine forest are applied to each model term in its new form. For pine forest, the equation describing evaporation rates can be reduced to a single term. Describing savannah evaporation, the aerodynamic conductance is modelled in two different ways and subsequent values of calibrated parameters within the bulk stomatal response function are found to be strongly dependent on this. The model dependence of such parameters is more easily understood with equations in normalised form. A sensitivity analysis of the Penman-Monteith model to all driving variables is performed for both savannah and pine forest data.