Wind Erosion in Western Queensland Australia

Chapter 7 – Land Erodibility Dynamics 1980-2006A number of factors affect model performance in the Simpson Desert. Firstly, sub-grid scaleaveraging of vegetation cover over the model 5 x 5 km grid cells resulted in an inability todetect narrow (10-15 m) erodible dune crests that have an average spacing of ~500 m (Purdie,1984). Secondly, the Aussie GRASS simulations of herbaceous vegetation cover, used asinput to AUSLEM, are driven by a plant growth-death-consumption scheme (Carter et al.,1996). The Simpson Desert is delineated as a National Park, so plant consumption rates in theAussie GRASS model are kept low (low effective stocking rates), resulting in consistentlyhigh predictions of grass cover. Finally, fire burn scars were not delineated in the model inputdata. In November 2001 and January 2002 extensive burning of the Simpson Desert resultedin the denudation of ~4000 km 2 (10%) of the bioregion. These events resulted in aproportional increase in the area of the bioregion susceptible to wind erosion. However, theburn scars had not been included in the model input data at the time of acquisition so themodel has indeed underestimated the extent of erodible land between 2001 and 2006. Theseissues highlight the importance of data resolution and currency in the performance ofspatially explicit wind erosion models. Updating the model inputs to account for fire burnscars and running the model at a higher spatial resolution, e.g. 30 m, would be required toimprove model performance in the Simpson Desert bioregion.7.6.2 Temporal Patterns in Land ErodibilityFactors affecting temporal patterns in land erodibility include: climate, in particular rainfallquantities and distribution; land management practices, manifested here through stockingrates that affect the model grass cover inputs, and finally; the sensitivity of the bioregions tothese external forcing mechanisms as governed by geomorphology, soil characteristics andvegetation structure and resilience. Seasonal variations in land erodibility are weak but followa north-south spatial pattern in response to differences in rainfall seasonality across westernQueensland (Figure 7.4). The lack of robust correlations between annual rainfall, the SOI,PDO and land erodibility can be attributed to the complex interaction of these factors andlags in the landscape response to climate variability. The length of the data time-series (27years) also affected the results. In particular, interpretations of the influence of inter-decadalvariations in the PDO should be treated with caution.183