Wind Erosion in Western Queensland Australia

Chapter 5 – Land Erodibility Model Developmentpresence of barren floodplains (Quilpie) which provide dust source areas close to thesestations.Results indicate that at annual time scales land erodibility can be effectively modelledwithout incorporating a specific soil erodibility sub-model. However, AUSLEM did notperform well at small scales (i.e. within areas 25 x 25 km) when land erodibility was drivenby soil erodibility. The similarity of land erodibility trajectories for different areas around thestations (Figure 5.5b) suggests that AUSLEM shouldn’t be used to differentiate specificvariations at the land type scale (~50 km 2 ). Differences in land erodibility detected byAUSLEM are due to spatial and temporal variations in grass cover and soil moisture. If oneland type is depleted of vegetation and soil moisture it will have a higher indicated erodibilitythan an adjacent land type. This would lead to the differences in magnitude of erodibilityvalues at different AOI orientations (5.5b). Once a land type becomes bare, and landerodibility is determined by soil erodibility, AUSLEM cannot detect specific temporalchanges in susceptibility to wind erosion. Hence, the land erodibility trajectories were similarfor various AOI positions around the stations. The result demonstrates that the assumptionthat vegetation cover and soil moisture conditions are adequate predictors of land erodibility(Section 5.3.3) is scale dependent, and is only applicable when assessing landscape (10 3 km 2 )to regional (>10 4 km 2 ) scale patterns in land erodibility. At smaller spatial scales theimportance of soil erodibility in driving temporal variations in land erodibility will increaseand the performance of models that do not account for this will suffer. This outcome clearlydemonstrates the requirement for research to parameterise soil erodibility models like thatdeveloped in Chapter 4.Model output and dust-event frequency trajectories were consistently found to be dissimilarin 1981-82, 1986-87 and in 1990. These were years in which rainfall was anomalously low orhigh at areas within the study region relative to the preceding year. The poor match oftrajectories reflects either poor model performance, or differences in land erodibility drivenby these rainfall conditions, with areas of high erodibility outside the station AOIs affectingdust-event frequencies recorded at the stations. This is shown for 1982 when a short intensedrought affected the study region. In that year dust-event frequencies increased at Quilpie,Thargomindah, Birdsville and Longreach while land erodibility did not as residual grasscover around the stations was still high from the previous year. Table 5.1 indicates thatduring the periods when the trajectories were not synchronised there were significant153