Automated calibration of a physically based hydrologic model to simulate water balance variables for water and crop management

Winter cover cropping may mitigate the adverse effects of conventional cropping practices (bare soil during winter) by reducing runoff and increasing infiltration of rainfall. However, cover crops also deplete water through evapotranspiration. An experimental study with numerical modeling was conducted to investigate the effects of cropping practices on water balance variables.; Suitability of soil hydraulic parameters derived from direct and indirect methods as input in MIKE SHE, a physically based hydrologic model, to simulate soil water content (SWC) was studied. An automated calibration procedure was adopted in MIKE SHE in conjunction with PEST (parameter estimation model) to optimize effective parameters based on measured SWC data. A calibration-validation protocol was developed considering sensitivity of the parameters, nonuniqueness of the calibrated parameters, number of parameters to be optimized, and different calibration windows. The calibrated model was then used to simulate water balance variables. Finally, hypothetical scenarios were studied to investigate the effects of cropping practices on water availability.; The equally accurate MIKE SHE simulations of SWC data, using parameter sets obtained from average soil data with the indirect method and from plot specific data with the direct method, imply that the parameter set using easily collectable data can be as good as that using complicated and tedious field tests. However, the performance of the parameter set obtained from the automatic calibration procedure is superior to that from the traditional approach (field tests and published values) in the simulation of SWC data.; The experimental results indicated that cropping practices do not significantly affect SWC; rather crop rotation and soil spatial variability largely influence water distribution and availability in the subsurface system. The modeling results were consistent with the observed data. Simulation analyses indicated that cover cropping may not be a viable option in semiarid regions; however, the practice may increase infiltration in humid regions. Early cover crop termination and surface mulch in semiarid regions could increase the water availability and protect the soil surface from raindrop impact thus enhancing infiltration. Pre-irrigation before or during cover cropping period may increase water availability and improve cultivation activities.