Geostatistically Derived Great Lakes USLE Monthly Rainfall Erosivity Factors

The R factor, an index of rainfall erosivity in the universal soil loss equation (USLE), fundamentally governs water related soil loss from agricultural plots and is based on well studied empirical relations. Soil particles and adsorbed contaminants from agricultural runoff inevitably end up in water-courses and ultimately the Great Lakes system, disturbing natural habitat, reducing water clarity and quality. We here use over 22 years of records containing hourly precipitation recordings for 453 meteorological-recording sites in Ontario, southwestern Quebec, Michigan, Ohio, Pennsylvania, and New York to estimate the R factor surrounding the lower Laurentian Great Lakes. We generate annual and monthly R factor maps for the major growing season months using geostatistical interpolation. Our annual and seasonal maps can help in land use planning within the regions of intense agriculture surrounding Lakes Huron, Erie, and Ontario. Moving north of the Great Lakes, we find greater proportional errors on estimated R values because of low meteorological-recording site density. We find a strong northeast trend in decreasing erosivity of rainfall in the study area. The mean R value for 453 sites was 1,599.13 MJ mm−1 ha−1 yr−1, with a standard deviation of 591.74 MJ mm−1 ha−1 yr−1. Results are in general agreement with other published work but show some spatial differences due to climatic and physiographic variations across our study area.