Soil water balance: Comparing two simulation models of different levels of complexity with lysimeter observations

The simulation of the water balance in cropping systems is a useful tool to study how water can be used efficiently. However, this requires that models simulate water balance accurately. Beyond the typical comparison of model outputs with field observations, in this study we present the inter-comparison of models of different complexity with the same field dataset as a powerful method to assess model performance. The compared models were DSSAT (Decision Support System for Agrotechnology Transfer) and WAVE (Water and Agrochemicals in soil, crop and Vadose Environment), both describing one dimensional water transport. The soil water balance in DSSAT uses a simpler “tipping bucket” approach, while the more mechanistic WAVE integrates Richardʹs equation. The soil parameters were calibrated by using the Simulated Annealing (SA) global optimizing method. A continuous weighing lysimeter in a bare fallow provided the observed values of drainage and evapotranspiration (ET) while soil water content (SW) was supplied by capacitance sensors. An automated weather station recorded the weather data. After optimizing soil parameters with SA, both models performed well simulating the soil water balance components for the calibrated period. The use of cumulative values for ET and drainage in the optimization was more effective than using their daily values. For the validation period, the models predicted well soil evaporation over time but there were differences between models in the soil water and drainage simulations. In particular, WAVE predicted drainage well while DSSAT presented larger errors in the cumulative values. That could be due to the mechanistic nature of WAVE against the more functional nature of DSSAT. Further studies should be conducted to improve the quality of DSSAT drainage simulations. The good results from WAVE indicate that, after soil calibration, it could be used as a reasonable substitute for other models for periods when no drainage field measurements are available.