A refined regional modeling approach for the Corn Belt - experiences and recommendations for large-scale integrated modeling

Authors: PANAGOPOULOS, YIANNIS - Iowa State University; GASSMAN, PHILIP - Iowa State University; JHA, MANOJ - North Carolina Agricultural And Technical State University; KLING, CATHERINE - Iowa State University; CAMPBELL, TODD - Iowa State University; SRINIVASAN, RAGHAVAN - Texas A&M University; White, Michael; Arnold, Jeffrey

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2015
Publication Date: 3/7/2015
Publication URL: http://handle.nal.usda.gov/10113/61018
Citation: Panagopoulos, Y., Gassman, P.W., Jha, M.K., Kling, C.L., Campbell, T., Srinivasan, R., White, M.J., Arnold, J.G. 2015. A refined regional modeling approach for the Corn Belt - experiences and recommendations for large-scale integrated modeling. Journal of Hydrology. 524:348-366.

Interpretive Summary: Pollution from agriculture is the main source of nitrogen and phosphorus in the stream systems of the Corn Belt region in the Midwestern U.S. The SWAT model was used in this study to evaluate the potential impact of alternative land management practices on water pollution. In this study SWAT was applied at a very high resolution over a large area, which presents a number of challenges. This very complex model was adjusted to represent local water quality conditions using automated methods.

Technical Abstract: Nonpoint source pollution from agriculture is the main source of nitrogen and phosphorus in the stream systems of the Corn Belt region in the Midwestern U.S. This region is comprised of two large river basins, the intensely row-cropped Upper Mississippi River Basin (UMRB) and Ohio-Tennessee River Basin (OTRB), which are considered the key responsible contributing areas for the Northern Gulf of Mexico hypoxic zone according to the U.S. Environmental Protection Agency. Thus, in this area it is of utmost importance to ensure that intensive agriculture for food, feed and biofuel production can coexist with a healthy water environment. To address these multiple objectives within a river basin management context, an integrated modeling system is under construction with the hydrologic Soil and Water Assessment Tool (SWAT) model, capable of estimating river basin responses to alternative cropping and/or management strategies. To improve modeling performance compared to older studies and provide a basis for optimizing the cost-effectiveness of agricultural management, the SWAT Corn Belt application incorporates a greatly refined subwatershed structure based on the 12-digit hydrologic units or 'subwatersheds' as defined by the US Geological Service. Given the very large scale, the huge data required and the need to ensure the reliability of flow and pollutant load predictions at various locations within such hydrologic systems, a model’s setup, calibration and validation become time-demanding and challenging tasks. The purpose of the article is to present comprehensively all steps of this huge modeling exercise, providing annual and seasonal estimates of pollution in the region as well as spatial estimates of nutrient pollution and crop production through mapping. The predictions were based on a semi-automatic hydrologic calibration approach for large-scale and spatially detailed modeling studies, with the use of the Sequential Uncertainty Fitting algorithm (SUFI-2) and the SWAT-CUP interface, followed by a manual water quality calibration on a monthly basis. The refined modeling approach developed in this study led to successful predictions across most parts of the Corn Belt region and can be considered a solid basis for testing pollution mitigation measures and agricultural economic scenarios, providing useful information to policy makers and guidance on similar efforts at the regional scale.