The climate of the Arckaringa subregion has been described by Allan (1990) and McMahon et al. (2005) as arid; while Stern et al. (2000), using a modified version of the Köppen climate scheme, describes the region as ‘desert’. Weather in the subregion tends to be dominated by persistent high pressure systems; the location of the dominant high pressure system is an important influence on temperature in the region. Average maximum peak-summer monthly temperatures range between 35 °C and 38 °C, although daily maximums are regularly above 40 °C. In contrast, the minimum peak-winter monthly temperatures range from 5 °C to 6 °C, although daily minimums may drop below 0 °C, with monthly averages shown in Figure 7.
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Figure 7 Monthly maximum and minimum temperature
Source: Bioregional Assessment Programme (2014)
Mean annual rainfall varies between 130 and 170 mm across the majority of the region, with higher totals in excess of 200 mm found in the higher reaches of the Stuart Range and Denison and Davenport Range (Figure 8). Averaged across the region, the long term mean annual rainfall is 153 mm. The variability of rainfall over the subregion is both spatially and temporally among the highest in Australia (Allan, 1985). Key rainfall events in the subregion range from convective thunderstorms with limited spatial extent, but often with high intensities, to large transient depressions of tropical origin (Allan, 1985; Croke et al., 1999) that result in regional flooding. Although the majority of rainfall in the Arckaringa subregion occurs in the summer months, significant winter rains are not uncommon (Costelloe et al., 2005). This can be seen in Figure 9 where although there is little variation in the mean monthly precipitation depth, the extremes of rainfall in the summer months are very significant.
Figure 8 Mean annual rainfall in the Arckaringa subregion
Figure 9 Monthly precipitation depths
Source: Bioregional Assessment Programme (2014)
Table 3 shows rainfall summaries for selected sites in the Arckaringa subregion, with their locations shown in Figure 10. Of note is that the influence of summer monsoonal rains seems to diminish towards the south of the region. The northernmost site, Oodnadatta, receives over 40% of its annual total in the summer months (December – February). Further south, Coober Pedy, receives around 35% of annual falls in the same period and the southernmost site, Tarcoola, (Bulginna) only 28% in that period. These observations highlight the complexities inherent in water resource modelling in this area.
Table 3 Rainfall summary for selected sites in the Arckaringa subregion
As seen in Figure 11 and Figure 12, mean annual point potential evapotranspiration (PET) and pan evaporation increase on a general north-east gradient, with PET varying from 2150 mm in the south-west to 2750 mm in the north-east. Pan evaporation ranges from 2620 mm to 3200 mm along the same axis, with a small area of high evaporation in the south-west corner of the region.
Figure 10 Location of weather monitoring stations in the Arckaringa subregion
Figure 11 Mean annual point potential evapotranspiration in the Arckaringa subregion
Figure 12 Mean annual pan evaporation in the Arckaringa subregion
Until recently, there has been no dedicated research towards assessing the impacts of a changing climate over the Arckaringa subregion. Information produced through the Australian Climate Change Science Program has demonstrated that it is very likely that mean annual rainfall totals will decrease in future and that mean temperatures will increase. These findings are summarised in Figure 13 and Figure 14 respectively. It can be seen that median annual rainfall totals may fall by between 5% and 20% in the Arckaringa subregion by 2050, with temperatures increasing by 1 to 2.5 °C by the same time horizon.
Source: CSIRO et al. (2007a)
Source: CSIRO et al. (2007b)
Recently, the South Australian Government, through its Impacts of Climate Change on Water Resources Project, has undertaken an analysis of groundwater recharge, surface water runoff and rainfall intensity data in the South Australian Arid Lands Natural Resources Management (SAALNRM) Region to determine the potential impact of climate change on the principal water resources of the region (Gibbs et al., 2012). The SAALNRM Region contains most of the north-east of SA, running from the borders with the NT and Queensland to the north and east, with its western boundary around 100 km west of Coober Pedy and southernmost point around 300 km below the most southern point of the Arckaringa subregion, thereby bisecting and containing much of the Arckaringa subregion. This report found that rainfall decreases of the kind suggested by CSIRO et al. (2013) across the NRM region would lead to even more significant decreases in annual runoff totals, in the order of a 1% decline in annual rainfall representing a 2% decline in annual runoff. Gibbs et al. (2012) also determined that in the Neales-Peake catchment (cf Section 1.1.5.1.1), the length of time between flow events increased in line with rainfall declines, (i.e. a 10% reduction in annual rainfall led to a 10% increase in average length of dry periods) a statistic potentially more important given the intermittent nature of flow events in the subregion.
