Wind Erosion in Western Queensland Australia

Chapter 8 – ConclusionsThe third aim of this thesis was to validate the performance of the land erodibilitymodel. This was achieved through the fifth and sixth research objectives: to develop amethod for visually assessing land erodibility at the landscape scale; and to employ the visualassessments of land erodibility and observational records of wind erosion activity to validatethe model.The first approach for model validation drew on a comparison of time-series modelassessments of land erodibility with observational records of wind erosion activity acrosswestern Queensland (Chapter 5). The observational data included records of locally blowingdust, dust storms, dust hazes, and dust whirls. The validation was conducted at eightmeteorological stations located across the four bioregions covering the study area. A crosscorrelationapproach was used to examine the synchronisation of trends in modelled landerodibility, annual total dust-event frequencies, and mean annual 3 pm wind speeds at fourspatial length scales (from 25 to 150 km) between 1980 and 1990. The model output hadstrong correlations with dust-event frequencies at half of the validation stations. The modelagreement with trends in dust-event frequencies varied across spatial scales and was highlydependent on land type variability around the reference stations. Poor correlations at the otherstations were linked to limitations of the model, i.e. the lack of a soil erodibility scheme, andthe coarse spatial resolution of the model input data. The validation was also affected by thetypes of dust events used in the validation process. Dust source areas for dust storms and dusthazes cannot be detected from the observational data and so these event types did not alwaysprovide good records of wind erosion activity by which model performance could beassessed.The second approach for model validation relates to the fifth objective of this thesis. Thatwas, to develop a method for visually assessing land erodibility that can be used to monitorrangeland conditions at the landscape scale (Chapter 6). This objective was addressed byestablishing criteria for evaluating land erodibility based on empirical relationships betweensoil texture, vegetation cover, land type characteristics, and wind erosion. The criteria werethen used to visually assess land erodibility over long distances (10 3 km) on vehicle-basedtransects run through the western Queensland rangelands. To validate the model, datacollected on the transects were compared with model assessments of land erodibility at a 200x 200 m spatial resolution in five sub-sections of the study area. The comparison indicatedthat AUSLEM performs better in the open grasslands of the western Mitchell Grass Downs192