Simulation of water use and herbage growth in arid regions : a re-evaluation and further development of the model ‘arid crop’

A previously published simulation model, describing growth of annual pasture under semi-arid conditions, is re-examined and further developed on the basis of additional experimental information. Major changes introduced are connected with the partitioning of above-ground dry matter into leaves and non-leaf material and with the influence of drought on the photosynthetic performance of the vegetation. It is concluded that the present description yields satisfactory results for varying environmental conditions. Further study is required, however, especially with respect to the influence of prolonged water shortage on phenology, the ability to survive and the regrowth potential. A sensitivity analysis showed that the model is not very sensitive to variations in weather parameters, except for rain and, to a lesser extent, air temperature. It may, therefore, be applied with reasonable confidence, even when other weather data are available from nearby locations only.