Wind Erosion in Western Queensland Australia

Chapter 5 – Land Erodibility Model DevelopmentSoil erodibility is governed by soil texture, but varies with changes in moisture, aggregationand surface crusting (Zobeck, 1991; Merrill et al., 1999). These factors affect the strength ofcohesive forces between soil particles and the availability of loose erodible sediments on thesoil surface. Together these conditions act against drag and lift forces associated with windshear. The effect of non-erodible elements like vegetation is through a partitioning of windshear stress between roughness elements and the soil surface, resulting in an increase inroughness length and potential decrease in wind erosivity (Marshall, 1971; Raupach et al.,1993). Factors controlling land erodibility include those affecting soil erodibility, land typecharacteristics (vegetation and geomorphology), climate (rainfall, radiation balance,windiness) and management (Figure 5.2). Where non-erodible roughness elements are absent,land erodibility is controlled by soil erodibility.The term land erodibility implies a relative susceptibility of land areas to wind erosion.Factors controlling soil and land erodibility operate at a range of spatial (local to global) andtemporal (seconds to years) scales. Climate variability and land management factors drivechanges in soil erodibility and surface roughness conditions within a landscape. Thisvariability means that soil and land erodibility are spatio-temporally dynamic through acontinuum (Geeves et al., 2000; Chapter 2, Section 2.1).5.3.2 Rationale for Model DevelopmentWebb et al. (2006) reported the development of an Australian Land Erodibility Model(AUSLEM) through the specification of a threshold-based rule-set. The rule-set definesconditions under which the Australian landscape may become susceptible to wind erosion.AUSLEM assigns land erodibility rankings through the rule-set, which is applied to inputs ofsoil texture (sand, silt and clay content), and mean monthly grass cover (%), soil moisture(mm per 10 cm profile) and rainfall (mm). The model is run using monthly-average 5 x 5 kmgridded inputs of grass cover, soil water content and rainfall obtained from the AussieGRASS pasture growth model (Carter et al., 1996a) and Bureau of Meteorology. Soil texturalinput data were acquired from the Australian Natural Resources Atlas (see DEWHA, 2007).The model did not account for tree or stone cover effects on wind erosion.Webb et al. (2006) applied AUSLEM to assess land erodibility on a national basis underrepresentative “wet”, “normal” and “dry” conditions. The model demonstrated an ability to134