Wind Erosion in Western Queensland Australia

Chapter 4 –Modelling Soil Erodibility Dynamicswhere b min defines the minimum erodibility occurring at t = 1, and b max defines the maximumerodibility of a soil as t → ∞. Using this framework, temporal changes in soil erodibility canthen be regulated by rainfall occurrence and time since rainfall, which can be used to derivevalues of t and input into Equation (4.11).Antecedent rainfall conditions have demonstrated links with wind erosion activity at bothshort (daily to weekly) and long (e.g. monthly to seasonal) time scales. The effect ofantecedent rainfall on soil erodibility at short time scales is manifested through soil wetness(moisture) conditions that drive inter-particle binding (Belly, 1964; McKenna-Neuman andNickling, 1989; Fécan et al., 1999). The period for which soil wetness will affect erodibilityis dependent on the water holding capacity of a soil, as determined by the soil texture,chemical and biological properties and vegetation cover (Cornelis and Gabriels, 2003). Whilethe asymptotic form of the erodibility growth curve could be used to cover soil moistureeffects on erodibility, the model does not explicitly account for moisture effects on grainbinding (see Section 4.6 for discussion). At long time scales (e.g. monthly to seasonal)antecedent rainfall has been shown to affect both soil crust condition (Strong, 2007) and winderosion activity (Brazel and Nickling, 1986; Yu et al., 1993; Neil and Yu, 1994).Considering application of the model for daily simulations of soil erodibility, we can denotet init as the value for t (Equation 4.11) used to initiate a simulation, t prev as the value for t on theprevious simulation day, and t new as the value for t on the simulation day. Values for t init canbe approximated by considering antecedent rainfall totals for long (∑R) and short (∑r)periods prior to a simulation day. Values for t new can be updated from t init (and t prev ) byconsidering short term rainfall totals up to and including the simulation day. Under thisframework conditional statements can be used to assign values for t init based on ∑R, forexample:t init = W for ∑ R < W r (4.13)= X for W r < ∑ R < X r= … …= 1 for ∑ R > Y rwhere W r and X r … are antecedent rainfall ranges determining values for t init based on ∑R. Forrainfall above a threshold sufficient to initiate surface crusting (denoted Y r ), t init will be set to1 such that b(t) = b min and the resulting soil erodibility is equal to Q min . In terms of Figure 4.3,115