Wind Erosion in Western Queensland Australia

Chapter 5 – Land Erodibility Model Development5.5 Model Application and ValidationLand erodibility cannot be directly measured in the field, so proxy measures that indicatewind erosion hazard must be used for validation. While wind erosion rates are relativelyeasily measured at small scales (i.e. individual fields), and have been used to validate modelssuch as RWEQ, WEPS, TEAM and IWEMS (Hagen, 1991; Fryrear et al., 1998; Lu and Shao,2001), finding indicators of land erodibility at the regional scale at which AUSLEM operatesis problematic. The objective of the validation was to compare time series trajectories ofmean annual AUSLEM output with trends in dust-event frequencies and wind speeds atlocations across the study area. The validation hypothesis was that at annual time scales dusteventfrequencies are highly dependent on regional land erodibility and suitable wind speeds,so temporal trends in time-series of these should display similar patterns. Cross-correlationanalysis of dust-event frequencies, mean wind speeds and modelled land erodibility wasidentified as a means for quantifying the similarity of their temporal trends and thereforemodel performance.5.5.1 MethodologyDust-event records (Observation codes 05-09 and 30-35) and mean annual 3 pm local windspeeds (ms -1 ) were extracted from the Bureau of Meteorology (BoM) database for 16 stationswithin the study area for the period January 1980 to December 1990. This period was chosento avoid overlap with the dust-event data used to derive the model soil moisture function(1991-2006). Mean annual wind speeds were selected to provide an indicator of windiness atthe same temporal resolution as the model output. Annual total event frequencies werecomputed for each station, and these were linked in a database to the mean wind speed data.Eight of the 16 stations had recorded >1 event in every year, and these were used forcomparison with AUSLEM output predictions (Figure 5.1). Four classes of dust-eventobservations were created to assess the effects of using different event types in the validation.The classes included: 1) all dust-event types; 2) events with hazes (Codes 05, 06) removed; 3)events with hazes and whirls (+ Code 08) removed; and 4) the Dust Storm Index (DSI), acomposite index of local, moderate and severe dust-event frequencies (McTainsh and Tews,1998).143