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 their fast-growth rate and coppicing ability. However, their water use efficiency along with the adverse environmental impacts is still a controversial issue. In this study, a system dynamic model was developed to estimate 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 both calibrated and validated with very good agreements between model predictions and field measurements obtained from our experiment. Two simulation scenarios were employed in this study, one was to quantify 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 soil conditions upon the eucalyptus water use. A characteristic monthly variation pattern was found for soil evaporation, leaf transpiration, and root uptake, with increasing from winter to summer and decreasing from 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. The maximum rate of leaf transpiration was about five times greater than that of soil evaporation. The cumulative annual water use by the eucalypts was 690,000 L/plot (or 3200 L/tree). Although no differences in ET rate and water use were found between the base and wet soil conditions, the discernable discrepancies in ET rate and water use were observed between the wet and dry soil conditions when the soil water content was below 0.17 cm3/cm3. This study suggests that the system dynamic model developed with STELLA is a useful tool to estimate soil hydrological processes and water use in a eucalypt plantation.