Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2012
Publication Date: 4/5/2013
Citation: Bonuma, N.B., Rossi, C.G., Arnold, J.G., Reichert, J.M., Paiva, E.M. 2013. Hydrology evaluation of the Soil and Water Assessment Tool considering measurement uncertainty for a small watershed in southern Brazil. Applied Engineering in Agriculture. 29(2):189-200. Interpretive Summary: Brazil has one of the world’s largest fresh water reserves, however, it is not distributed uniformly throughout the country. A lack of management and pollution reduce the amount of quality water available. The intensively-cultivated croplands in Southern Brazil have impacted the area’s water balance and are a source of environmental contamination. A computer-based simulation was used to evaluate hydrologic changes in the Arroio Lino watershed due to agricultural activities. The Soil and Water Assessment Tool watershed scale model did not capture the daily surface runoff peaks well and was unable to represent the short duration, high intensity storms that frequently occur in this watershed. Runoff that was underestimated during low flow periods may be due to uncertainty in estimating runoff from daily rainfall. Limited measured data and short calibration and validation periods may have also impacted the simulation results. The model was able to predict reliable estimates for evapotranspiration and identified that baseflow impacts the study area’s water system more so than surface runoff.
Technical Abstract: Areas under intensive tobacco crop cultivation have impacted the water balance and have become sources of environmental contamination in Southern Brazil. Correct determination of the area’s hydrology is essential since it is the driving force of sediment and nutrient loading dynamics. The Soil and Water Assessment Tool (SWAT) model, version 2009, was used to evaluate hydrological processes for the Arroio Lino watershed, located in the Brazilian state of Rio Grande do Sul. The measured discharge at the watershed outlet was used for model streamflow model sensitivity to selected parameters, calibration, and validation from 2001 to 2005. A Latin Hypercube (LH) and One-factor-At-a-Time (OAT) sensitivity analysis was performed on 27 input variables. Model calibration was performed with the Shuffled Complex Evolution Algorithm-Uncertainty Analysis (SCE-UA). Time series plots and standard statistical measures were used to verify model predictions. The most sensitive parameters for runoff were curve number (CN2), soil evaporation compensation factor (ESCO), and baseflow alpha factor (ALPHA_BF). The predicted monthly streamflow matched the observed values, with a Nash–Sutcliffe coefficient of 0.87 and 0.76 during calibration and validation, respectively. The results suggest that the SWAT model is a promising tool to evaluate hydrology in Brazilian watersheds, especially on a monthly basis. The calibrated hydrologic model can be used for further analysis of climate and land use changes and to investigate the effect of different management scenarios on stream water quality.