Some challenges in hydrologic model calibration for large-scale studies: A case study of SWAT model application to Mississippi-Atchafalaya River Basin

Authors: KANNAN, NARAYANAN - Tarleton State University; SANTHI, CHINNASAMY - Texas Agrilife Research; White, Michael; MEHAN, SUSHANT - Formation Environmental Llc; Arnold, Jeffrey; GASSMAN, PHILIP - Iowa State University

Submitted to: Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2019
Publication Date: 2/10/2019
Citation: Kannan, N., Santhi, C., White, M.J., Mehan, S., Arnold, J.G., Gassman, P.W. 2019. Some challenges in hydrologic model calibration for large-scale studies: A case study of SWAT model application to Mississippi-Atchafalaya River Basin. Hydrology. 6(1):17. https://doi.org/10.3390/hydrology6010017.
DOI: https://doi.org/10.3390/hydrology6010017

Interpretive Summary: The Cropland Component of Conservation Effects Assessment Project (CEAP) was developed to quantify the environment impact of conservation practices on cultivated cropland across the United States. The Soil and Water Assessment Tool (SWAT) was used as the watershed model for CEAP. Calibrating the SWAT model across the entire U.S. poses many challenges and, in this study, we discuss those challenges and potential solutions when applying SWAT to the Mississippi-Atchafalaya River Basin. An automated calibration procedure was developed to calibrate surface runoff and groundwater flow. Based on the results obtained, our analysis pointed out multiple challenges to calibration such as: (1) availability of good quality data, (2) accounting for multiple reservoirs, (3) inadequate accounting of elevation and slopes in mountainous regions, (4) poor representation of sediment carrying capacity of channels, (5) inadequate capturing of irrigation return flows, (6) inadequate representation of vegetative cover, and (7) the coarse spatial scale of soils, land cover, and topography. From the lessons learned in the study, we are better able to calibrate the SWAT ecohydrological model, and thus have more confidence in our assessment of conservation practices and national conservation policy.

Technical Abstract: This study is a part of the Conservation Effects Assessment Project (CEAP) aimed to quantify the environmental and economic benefits of conservation practices implemented in the cultivated cropland throughout the United States. The Soil and Water Assessment Tool (SWAT) model under the Hydrologic United Modeling of the United States (HUMUS) framework was used in the study. An automated flow calibration procedure was developed and used to calibrate runoff for each 8-digit watershed (within 20% of calibration target) and the partitioning of runoff into surface and sub-surface flow components (within 10% of calibration target). Streamflow was validated at selected gauging stations along major rivers within the river basin with a target R2 of >0.6 and Nash and Sutcliffe Efficiency of >0.5. The study area covered the entire Mississippi and Atchafalaya River Basin (MARB). Based on the results obtained, our analysis pointed out multiple challenges to calibration such as: (1) availability of good quality data, (2) accounting for multiple reservoirs within a sub-watershed, (3) inadequate accounting of elevation and slopes in mountainous regions, (4) poor representation of carrying capacity of channels, (5) inadequate capturing of the irrigation return flows, (6) inadequate representation of vegetative cover, and (7) poor representation of water abstractions (both surface and groundwater). Additional outstanding challenges to large-scale hydrologic model calibration were the coarse spatial scale of soils, land cover, and topography.