Evaluating soil loss under land use management and extreme rainfall

Topsoil loss is a widespread environmental concern causing adverse impacts on natural and human systems. Severe weather accompanied with human activities can exacerbate this issue degrading soil health and consequently accelerating global and regional food insecurity. Erosion impairs soil physical and chemical properties such as infiltration rate, water holding capacity, loss of nutrients including soil carbon and nitrogen. Although, temporal properties of a rainfall event have meaningful implications, spatial heterogeneity of a rainfall contributes substantially and cannot be overlooked. Therefore, in this study, we investigated soil loss using weather radar NEXRAD data. We developed extreme rainfall (ER) scenarios and land use practices (nomgt, S0, S1, S2, and S3) and evaluated the watershed response. We found that grazing can manifold soil loss, and if accompanied with extreme rainfalls, soil loss accelerates impacting different subbasins each time. Our results suggest that spatial heterogeneity of ERs can be more significant in individual extreme rainfalls, however, over a year, soil moisture and type of the management practices (grazing and farming) could contribute more to topsoil loss. We classified watershed subbasins into different classes of soil loss severity to determine the soil loss hotspots. Soil loss can go as high as 350 (ton/ha/yr) under the ERs. Land use practices can increase erosion by 3600%. Slight increase in rainfall concentration (S1) can put vulnerable subbasins in extremely severe class (>150 ton/ha/yr). Under moderate increase in the rainfall concentration (S2) more subbasins fall into extremely severe category yielding approximately 200 ton/ha/yr. Under high increase in rainfall concentration (S3) almost all the subbasins fall into the extremely severe class yielding >200 ton/ha/yr. We found that in vulnerable subbasins, up to 10% increase in (Concentration Ratio Index) CI can increase annual soil loss up to 75%. Single ER can generate up to 35% of annual soil loss. Under one ER event soil loss hotspot subbasins can lose up to 160 ton/ha/day. 32% and 80% increase in rainfall amount for an ER event can increase soil loss by 94% and 285% respectively. The results, also, reveal that grazing and farming can be responsible for up 50% of soil loss. Our findings indicate the importance of site-specific managements to mitigate soil loss and all the consequences. Our study can help in better soil loss management implementation. Insights of our study may also help in water quality control and flood mitigation planning efforts.