Wind Erosion in Western Queensland Australia
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Wind Erosion in Western Queensland Australia

Modelling Land Susceptibility to Wind Erosion in Western ... - Ninti One Modelling Land Susceptibility to Wind Erosion in Western ... - Ninti One

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Chapter 7 – Land Erodibility Dynamics 1980-2006Land areas with consistently low and no erodibility occur across the northern and easternboundaries of the study area in the Mitchell Grass Downs and Mulga Lands (Figure 7.2). Thisis consistent with the regions receiving on average the highest annual rainfall across the studyarea (McTainsh and Leys, 1993). The Channel Country frequently has an elevated landerodibility ranking. The only areas of the bioregion that consistently have no erodibility arethe gibber plains (stony country) and inner-floodplains of the Cooper, Diamantina andGeorgina river systems. The land area extending between Coopers Creek and the BullooRiver had a low erodibility for much of the period between 1980 and 2006 (Figure 7.2). Thisis interesting given that surrounding regions generally had higher erodibility rankings. In thesouth-eastern corner of the study area the mulga plains around Charleville generally have alow susceptibility to wind erosion (Figure 7.3). Extensive surficial stone cover (gibbers) andhigh tree cover levels reduces the erodibility of these areas. The model identified the SimpsonDesert bioregion as having consistently low land erodibility.Together the areas identified as having high to moderate land erodibility match the spatialpattern of areas recording the highest dust-storm frequencies in the north-eastern half of theLake Eyre Basin (Middleton, 1984; Burgess et al., 1989; McTainsh et al., 1990). Dust-stormfrequencies decline to the east of Longreach and Charleville (Figure 7.1) and the modelassessments of land erodibility are consistent with this pattern. Miles and McTainsh (1994)and McTainsh et al. (1999) reported high spatial variability in wind erosion activity in theChannel Country and Mulga Lands. This is reflected in the heterogeneity of land erodibilityin these regions (Figure 7.2).7.5.2 Temporal Dynamics in Land ErodibilitySeasonal VariationsFigure 7.4 presents graphs of mean monthly land erodibility for eight meteorological stationsin western Queensland. Land erodibility has weak seasonality. The strength of seasonalvariations changes across the study area and between land types. The largest seasonalvariations occur at Quilpie (range 0.027), Thargomindah (range 0.018) and Urandangie(0.01). The smallest variations occur at Boulia (range 0.004), Charleville (range 0.003) andWindorah (range 0.001).176

Chapter 7 – Land Erodibility Dynamics 1980-2006Figure 7.4 Graphs of mean monthly land erodibility (from 0: not erodible, to 1: high erodibility) foreight stations across the study area, based on modelled daily land erodibility data (1980-2006)extracted from areas with 50 km radius around the stations.There is a north-south spatial pattern in the seasonality of land erodibility across westernQueensland (Figure 7.4). Land erodibility reaches a maximum in spring (SON) and earlysummer (ND) in the Channel Country and Mitchell Grass Downs, and a minimum in latesummer (JFM) through to winter (JJA). In the Mulga Lands to the south of the study arealand erodibility peaks in spring (SON) and autumn (MAM), and reaches a minimum overwinter (JJA). These dynamics are consistent with seasonal patterns in dust-storm frequenciesreported by Eckström et al. (2004). The northern pattern reflects a dominance of summerrainfall associated with thunderstorm activity, and a reduction in grass cover through winterand spring associated with lower rainfall. The southern pattern reflects a tendency of the177

Chapter 7 – Land Erodibility Dynamics 1980-2006Figure 7.4 Graphs of mean monthly land erodibility (from 0: not erodible, to 1: high erodibility) foreight stations across the study area, based on modelled daily land erodibility data (1980-2006)extracted from areas with 50 km radius around the stations.There is a north-south spatial pattern <strong>in</strong> the seasonality of land erodibility across western<strong>Queensland</strong> (Figure 7.4). Land erodibility reaches a maximum <strong>in</strong> spr<strong>in</strong>g (SON) and earlysummer (ND) <strong>in</strong> the Channel Country and Mitchell Grass Downs, and a m<strong>in</strong>imum <strong>in</strong> latesummer (JFM) through to w<strong>in</strong>ter (JJA). In the Mulga Lands to the south of the study arealand erodibility peaks <strong>in</strong> spr<strong>in</strong>g (SON) and autumn (MAM), and reaches a m<strong>in</strong>imum overw<strong>in</strong>ter (JJA). These dynamics are consistent with seasonal patterns <strong>in</strong> dust-storm frequenciesreported by Eckström et al. (2004). The northern pattern reflects a dom<strong>in</strong>ance of summerra<strong>in</strong>fall associated with thunderstorm activity, and a reduction <strong>in</strong> grass cover through w<strong>in</strong>terand spr<strong>in</strong>g associated with lower ra<strong>in</strong>fall. The southern pattern reflects a tendency of the177

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