Skip to main content
ARS Home » Plains Area » Temple, Texas » Grassland Soil and Water Research Laboratory » Research » Publications at this Location » Publication #377328

Research Project: Resilient Management Systems and Decision Support Tools to Optimize Agricultural Production and Watershed Responses from Field to National Scale

Location: Grassland Soil and Water Research Laboratory

Title: SWAT ungauged: Water quality modeling in the Upper Mississippi River Basin

item QI, JUNYU - University Of Maryland
item ZHANG, XUESONG - Pacific Northwest National Laboratory
item YANG, QICHUAN - University Of Melbourne
item SRINIVASAN, R - Texas Agrilife Research
item Arnold, Jeffrey
item LI, JIA - Environmental Protection Agency (EPA)
item WALDHOLF, STEPHANIE - Pacific Northwest National Laboratory
item COLE, JEFFERSON - Environmental Protection Agency (EPA)

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2020
Publication Date: 2/1/2020
Publication URL:
Citation: Qi, J., Zhang, X., Yang, Q., Srinivasan, R., Arnold, J.G., Li, J., Waldholf, S.T., Cole, J. 2020. SWAT ungauged: Water quality modeling in the Upper Mississippi River Basin. Journal of Hydrology. 584:124601.

Interpretive Summary: Although the USGS has an extensive network of stream gages across the U.S., most rivers are not gaged to monitor flow, sediment, and nutrients. This limits how watershed models can be calibrated and validated, thus limiting confidence in model results. To assess the impact of limited data on model output, the SWAT model was applied to the Upper Mississippi River Basin. The model was also enhanced with physically based soil temperature and carbon balance modules. The improved model was shown to perform better in predicting stream flow, sediment loads, nitrates, and total nitrogen transported in the Mississippi River compared to previous uncalibrated models. This study shows the importance of using physically based process models, especially in watersheds that have limited monitored data for calibration and validation. This knowledge will provide more confidence in national modeling studies where data is not available across the entire country.

Technical Abstract: Improving model performance in ungauged basins has been a chronic challenge in watershed model application to understand and assess water quality impacts of agricultural conservation practices, land use change, and climate adaptation measures in large river basins. Here, we evaluate a modified version of SWAT2012 (referred to as SWAT-EC hereafter), which integrates an energy balanced soil temperature module (STM) and the CENTRUY-based soil organic matter algorithm, for simulating water quality parameters in the Upper Mississippi River Basin (UMRB), and compare it against the original SWAT2012. Model evaluation was performed for simulating streamflow, sediment, and nitrate-N (NO3-N) and total nitrogen (TN) loadings at three stations near the outlets of UMRB. The model comparison was conducted without parameter calibration in order to assess their performance under ungauged conditions. The results indicate that SWAT-EC outperformed SWAT2012 for stream flow and NO3-N and TN loading simulation on both monthly and annual scales. For sediment, SWAT-EC performed better than SWAT2012 on a monthly time step basis, but no noticeable improvement was found at the annual scale. In addition, the performance of the uncalibrated SWAT-EC was comparable to other calibrated SWAT models reported in previous publications with respect to sediment and NO3-N loadings. These findings highlight the importance of advancing process representation in physically-based models to improve model credibility, particularly in ungauged basins.