Reply to Comment on “determining soil erodibility for the USLE-MM rainfall erosion model by P.I.A. Kinnell”

In Kinnell (2018), I proposed that the soil erodibility factor K_UMM used in the USLE-MM model could be replaced by the product of the soil erodibility factor K_UM and a coefficient a1 that was given by the ratio of between K_UMM and K_UM. The theory was developed based on the well-known practice that for USLE based models, the erodibility factor is calculated as the ratio between the total soil loss for a set of erosion producing events and the total value of the erosivity index associated with those events. In their comment, Pampalone et al. (2018) used data for K_UMM and K_UM values for 12 plots at Sparacia determined by regression analysis to calculate a1 using a different method to show that the exponential equation I proposed in Kinnell (2018) between the power of the erosivity term and the a1 was demonstrated to be site dependent. In this reply, the approach adopted by Pampalone et al. is challenged for not using the well-known method for determining soil erodibilities in USLE based models and the consequences of power increasing with slope length while the runoff ratio decreases with slope length on the values of a1 is illustrated. At Sparacia, soil loss varies with K_UM, slope length, and slope gradient, and, in addition, in the context of the USLE-MM, consideration has to be given to the fact that both b1 and the runoff ratio vary with slope length.