Abstract
Agricultural system models are useful tools for tailoring agricultural production systems to possible climate variations.The objectives of this work were: (1) to evaluate and calibrate the water balance and crop components of the WaterErosion Prediction Project (WEPP) model and to make improvements if necessary, and (2) to simulate hydrologic and cropresponses to generated climate scenarios for winter wheat (Triticum aestivum L.). Precipitation, surface runoff, soil moisture,and wheat biomass collected between 1980 and 1996 on a 1.6 ha watershed near El Reno, Oklahoma, were used. Twocontrasting (wet and dry) climate scenarios were generated using a climate generator (CLIGEN) for assessing the overallsensitivity of WEPP to climate variations. Optimized saturated hydraulic conductivity (Ks) agreed well with field-measuredKs, indicating that the infiltration routine of the model functioned properly. WEPPs original water use function substantiallyoverpredicted plant water uptake and therefore was modified. The revised water use function resulted in better predictionsof soil water balance, plant water stress, and biomass production. Predicted aboveground biomass agreed relatively well withmeasured data (model efficiency = 0.5). However, wheat grain yields were less well predicted because of inadequateadjustments to harvest index in the model. The general relationship between total aboveground biomass and growing-seasonevapotranspiration for winter wheat was reasonably simulated by the model. Model simulations under the generated wet anddry scenarios showed that each percent increase in growing-season precipitation would result in, on average, 3.38%, 0.34%,0.73%, 1.09%, and 0.81% increases in surface runoff, plant transpiration, soil evaporation, deep percolation, and wheatgrain yield, respectively, under the study conditions. This work has shown that WEPP is capable of simulating hydrologicand crop responses to climate variations.
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