Extension of the revised wind erosion equation (RWEQ) to calculate grassland wind erosion rates based on the ¹³⁷Cs tracing technique

The commonly used wind erosion models, including the Revised Wind Erosion Equation (RWEQ), are mainly based on data from loose soils, for which the erodibility factor (EF) reflects the abundance of erodible aggregates, and cannot be applied to simulate erosion of compacted soils such as some grassland soils. Taking the Inner Mongolia Autonomous Region in northern China as the study area, we used the Cs-137 tracing technique to estimate the soil loss of grassland by wind erosion from 1963 to 2021, and used the results as criteria to verify the wind erosion rate (WER) predicted by RWEQ for the same period. We found that RWEQ accurately calculated the WER of cultivated farmland, but overestimated grassland WER. We believe that the main reason is that the equation did not consider the impact of soil compaction (SC) on EF, since the calculation methods for the weather factor, vegetation factor, surface roughness factor, and soil crust factor in RWEQ are applicable for grasslands. Therefore, we used the Cs-137 tracing results to extrapolate the grassland EF while keeping the climate, soil crust, vegetation cover, and roughness factors constant, and combined SC and the proportion of aggregates smaller than 0.84 mm in diameter to develop an empirical equation for grassland EF. Compared with the original model, the extended model (RWEQ(ext)) that included the factor of SC more accurately estimated the WER of compacted grassland soil and could be applied to the whole study area. The RWEQ(ext) results showed that tolerable and slight levels of wind erosion dominated the grassland and gobi surfaces in the study area, whereas moderate wind erosion occurred in grasslands with sparse vegetation cover, and severe, very severe, and destructive wind erosion mainly occurred on loose surfaces such as sandy land with low vegetation cover.