A system dynamic model to estimate hydrological processes and water use in a eucalypt plantation
Eucalypts have been identified as one of the best feedstocks for bioenergy production due to theirfast-growth rate and coppicing ability. However, their water use efficiency along with the adverse envi-ronmental impacts is still a controversial issue. In this study, a system dynamic model was developed toestimate the hydrological processes and water use in a eucalyptus urophylla plantation using the STELLA(Structural Thinking and Experiential Learning Laboratory with Animation) software. This model was bothcalibrated and validated with very good agreements between model predictions and field measurementsobtained from our experiment. Two simulation scenarios were employed in this study, one was to quan-tify the hydrological processes in a eucalypt plantation (40 m × 40 m) under a normal (a base scenario)sandy soil condition, while the other was to estimate the potential impacts of the wet and dry sandy soilconditions upon the eucalyptus water use. A characteristic monthly variation pattern was found for soilevaporation, leaf transpiration, and root uptake, with increasing from winter to summer and decreasingfrom summer to the following winter. Overall, the rates of evaporation, transpiration, evapotranspiration(ET), and uptake were in the following order: ET > root uptake > leaf transpiration > soil evaporation. Themaximum rate of leaf transpiration was about five times greater than that of soil evaporation. The cumu-lative annual water use by the eucalypts was 690,000 L/plot (or 3200 L/tree). Although no differences inET rate and water use were found between the base and wet soil conditions, the discernable discrepanciesin ET rate and water use were observed between the wet and dry soil conditions when the soil watercontent was below 0.17 cm3/cm3. This study suggests that the system dynamic model developed withSTELLA is a useful tool to estimate soil hydrological processes and water use in a eucalypt plantation.