| Summary: | Agricultural activities, as part of the natural resource management practice, impact soil and water quality at the watershed or catchment level. Field monitoring is often used to evaluate and acquire knowledge of the impacts of management practices on productivity and environment. Computer simulation models, after calibrated and validated, provide an efficient and effective alternative for evaluating the effects of agricultural practices on soil and water quality at the watershed level. The main objective is calibrate and validate the AnnAGNPS model relatively to runoff and peak flow using five hydrologic years data, for the rain and irrigation season. The study watershed is located in Portugal, and covers an area of 189 ha, divided into 18 fields belonging to four farmers. The climate is typically Mediterranean with continental influence, and the main crops are oat, tobacco, sorghum and maize. The calibration was done manually, but in a systematic away, in order to select values for the statistical parameters so that the model closely simulates runoff and peak flow. The results obtained in calibration and validation of the AnnAGNPS model, confirm a good or very good performance to simulate the peak flow and runoff volume at daily or event scale, in rainfall season. Also, the obtained results are a good indication of the validity of AnnAGNPS model to simulate runoff in irrigation to larger periods of time, for example irrigation season.
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