A simple model for predicting herbage production from rainfall in rangelands and its calibration using remotely-sensed data

This paper describes the development of a model for estimating herbage production from rainfall and evapotranspiration in rangelands and its calibration using a vegetation cover index derived from remotely-sensed data. The model operates on a time unit of 1 month and has a maximum of three calibration parameters: a water use efficiency term, a cover depletion rate and a term describing the percentage of tree and shrub cover present. The model can represent variability at the whole landscape level and is well-suited to calibration. Parameter values derived when the model is inverted show variations which can logically be associated with differences in land condition and grazing pressure. These parameter values make it possible to model differences in herbage production in a particular area under different rainfall conditions and in response to changes in land condition or the level of grazing.