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Published on: September 1, 2020
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Nitrate loading projection is sensitive to freeze-thaw cycle representation.
Qianfeng Wang1, Junyu Qi2, Jia Li3
1Joint Global Change Research Institute, Pacific Northwest National Laboratory and University of Maryland, College Park, MD 20740, USA.
Water Research
|September 5, 2020
Summary
Climate change significantly impacts nitrogen runoff. A new model (SWAT-FT) shows a 25% nitrate loading increase, unlike the older model
Area of Science:
- Environmental Science
- Hydrology
- Climate Modeling
Background:
- Nitrogen runoff from climate change causes eutrophication, algal blooms, and hypoxia.
- Accurate modeling of nitrate loading is crucial for effective mitigation strategies.
Purpose of the Study:
- To compare nitrate loading projections under climate change using an enhanced Soil and Water Assessment Tool with physically based Freeze-Thaw cycle representation (SWAT-FT) against the original SWAT model.
- To analyze changes in riverine nitrate loadings and their terrestrial contributions in the Upper Mississippi River Basin (UMRB) through the 21st century.
Main Methods:
- Utilized climate projections from five General Circulation Models (GCMs) under the Representative Concentrations Pathways (RCP) 8.5 scenario (1960-2099).
- Employed SWAT-FT, incorporating physically based freeze-thaw cycle representation, and compared its results with the original SWAT model.
- Analyzed changes in nitrate loadings and spatial distribution of surface and subsurface contributions relative to a 1960-1999 baseline.
Main Results:
- The original SWAT model projected a ~50% increase in riverine nitrate loadings by 2100, nearly double the ~25% increase projected by SWAT-FT.
- Significant discrepancies were found in the spatial distribution of nitrate loadings between the two models.
- SWAT-FT predicted greater nitrate leaching in northwestern UMRB due to simulated less frequent frozen soils, highlighting the sensitivity to freeze-thaw cycles.
Conclusions:
- Physically based freeze-thaw cycle representation is essential for accurate water quality modeling under climate change.
- Future nitrogen runoff reduction strategies must consider land management effects on freeze-thaw cycles for reliable water quality projections.
