Wind Erosion in Western Queensland Australia

Chapter 6 – Field Assessments and Model Validationchanges in vegetation cover at the low end (0 – 15%) of the cover range. This means thatmodelled erodibility values increase slowly through the ‘no’, ‘low’ and ‘moderate’ classes,then rapidly into the ‘high’ erodibility class. The flat distribution of the data is explained bythe variability in predicted values for the high erodibility classes, which indicate that themodel has difficulty in representing land erodibility at the high end of the ranking.Secondly, data scaling issues affect the accuracies of the visual assessments and modelpredictions of land erodibility. Both are dependent on the arrangement of vegetation in thelandscape and are affected by its anisotropic distribution in semi-arid rangelands (Okin,2005). Assuming a uniform distribution of cover, the model has a tendency to under-estimateerodibility when input pixel vegetation cover values are high. Conversely, visual assessmentsof erodibility may account for vegetation patchiness, leading to relative over-estimates ofland erodibility. This issue is particularly relevant in the Mulga Lands (Windorah, Quilpiescenes), which are characterised by small erodible patches within a broader matrix of wellvegetatedland (Pickup, 1985). Future research to address this limitation should examine:implementing the validation at multiple spatial scales; accounting for vegetation distributionin the visual assessments of land erodibility; and including measures of vegetationdistribution in the model simulations (Okin and Gillette, 2001).6.5 ConclusionsThis chapter has demonstrated that acquiring visual assessments of land erodibility over largedistances using long-range transects can be a useful approach for monitoring landscapecondition and testing the performance of regional scale (>10 4 km 2 ) land erodibility models.Results suggest that AUSLEM performs better in the western Mitchell Grass Downs andChannel Country (Mt Dot, Cadell, Bedourie scenes) than in the Mulga Lands (Windorah,Quilpie scenes). To the knowledge of the author the long-range transect approach describedin this chapter has not previously been applied to test the performance of a wind erosionmodel. Further development and application of methods for assessing land erodibility at thelandscape scale will improve our capacity for monitoring and modelling land degradationprocesses in remote desert environments.166