Incorporating a precipitation factor into the Soil Vulnerability Index

Authors: PHUNG, QUANG - University Of Missouri; THOMPSON, ALLEN - University Of Missouri; MCGEHEE, RYAN - Iowa State University; Baffaut, Claire; White, Michael

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Soil Vulnerability Index (SVI) classifies cropland erosion risk based on easily obtained soil properties. However, the original index focuses on the Upper Mississippi, Ohio, and Tennessee River basins and does not incorporate rainfall characteristics. This limitation can affect the interpretation of SVI beyond the original region. This study evaluated the performance of the SVI across 79 watersheds in the central and eastern United States using 30 years of monthly and annual sediment yields estimated with a computer simulation model. Statistical analyses showed that annual rainfall erosivity (EI) consistently outperformed annual precipitation as a predictor of sediment yield, particularly for areas with Moderately High or High erosion risk. Winter EI and precipitation were strong drivers of sediment yield differences. However, maps of winter EI were more consistent with maps of high risk watersheds than annual or summer metrics. Incorporating a rainfall erosivity threshold into the SVI framework would improve the consistency of SVI in the region with high annual or winter EI. For this region, increasing vulnerability by one class for areas that have a Low or Moderate erosion risk if slope = 0.5%, and for all areas that have a Moderately High erosion risk regardless of slope would enhance the interpretation of SVI beyond the original calibration region. Integrating this modification into conservation assessment needs and prioritization tools will allow planners to prioritize conservation interventions based on both landscape and climatic drivers of erosion risk. This analysis supports the current administration's priority of putting farmers first and supporting American Agriculture by ensuring that conservation efforts go where they are needed to support long-term agricultural production without negative effects on nearby streams.

Technical Abstract: The Soil Vulnerability Index (SVI) classifies cropland erosion risk based on slope and soil characteristics. However, the original index development focused on the Upper Mississippi, Ohio, and Tennessee River basins and did not incorporate rainfall characteristics, limiting its transferability to other regions. This study evaluated the performance of the SVI in diverse precipitation regimes across 79 watersheds in the central and eastern United States using 30-year SWAT+ sediment yield simulations. Statistical analyses assessed differences in sediment yield distributions between the original area of study and watersheds grouped by annual precipitation, annual rainfall erosivity (EI), and seasonal precipitation differences. Annual EI consistently outperformed annual precipitation as a predictor of sediment yield, particularly for areas classified as Moderately High or High SVI. Winter EI and precipitation were strong drivers of sediment yield differences starting at 1000 MJ mm.ha'¹ h'¹ yr'¹ for winter EI, and 400 mm for winter precipitation. Winter EI contours aligned more closely with high sediment yield watersheds than annual or summer metrics. Incorporating a rainfall erosivity threshold into the SVI framework would improve the consistency of SVI in the region with high annual or winter EI. For watersheds with annual EI = 4500 MJ mm ha'¹ h'¹ yr'¹ or winter EI = 1000 MJ mm ha'¹ h'¹ yr'¹, increasing vulnerability by one class for Low and Moderate HRUs if slope = 0.5%, and for all Moderately High HRUs regardless of slope would enhance the interpretation of SVI in regions with winter-dominant or high-intensity rainfall regimes.