11.4 Key future impacts and vulnerabilities
This section discusses potential impacts of climate change, mostly based on climate projections consistent with those described in Section 11.3. It does not take into account adaptation; this is discussed in Section 11.5 and in more detail in Chapter 17. Conclusions are drawn from the available literature. Very little information is available on social and economic impacts. Further details on potential impacts can be found in various synthesis reports (MfE, 2001; Pittock, 2003).
11.4.1 Freshwater resources
126.96.36.199 Water security
The impact of climate change on water security is a significant cross-cutting issue. In Australia, many new risk assessments have been undertaken since the TAR (Table 11.5). The Murray-Darling Basin is Australia’s largest river basin, accounting for about 70% of irrigated crops and pastures (MDBC, 2006). Annual streamflow in the Basin is likely to fall 10-25% by 2050 and 16-48% by 2100 (Table 11.5). Little is known about future impacts on groundwater in Australia.
Table 11.5. Impacts on Australian water security. SRES scenarios are specified where possible.
|Year ||Impacts |
- Change in annual runoff: -5 to +15% on the north-east coast, ±15% on the east coast, a decline of up to 20% in the south-east, ±10% in Tasmania, a decline of up to 25% in the Gulf of St Vincent (South Australia), and -25 to +10% in the south-west (Chiew and McMahon, 2002).
- Decline in annual runoff: 6-8% in most of eastern Australia and 14% in south-west Australia in the period 2021 to 2050 relative to 1961 to 1990 for the A2 scenario (Chiew et al., 2003).
- Burrendong dam (NSW): inflows change by +10% to 30% across all SRES scenarios, but the 90% confidence interval is 0% to -15% (Jones and Page, 2001).
- Victoria: runoff in 29 catchments declines by 0-45% (Jones and Durack, 2005).
- Murray Darling Basin: for B1, streamflow drops 10-19% and salinity changes -6 to +16%; for A1, streamflow drops 14-25% and salinity changes -8 to +19% (Beare and Heaney, 2002).
- Melbourne: a risk assessment using ten climate models (driven by the SRES B1, A1B and A1FI scenarios) indicated that average streamflow is likely to decline 7-35% (Howe et al., 2005); however, planned demand-side and supply-side actions are likely to alleviate water shortages through to 2020 (Howe et al., 2005).
- Burrendong Dam (NSW): inflows change by +5 to -35% across all SRES scenarios, for the 90% confidence interval (Jones and Page, 2001).
- Murray-Darling Basin: for B1, streamflow declines 16 to 30%, salinity changes -16 to +35%, agricultural costs US$0.6 billion; for A1, streamflow declines 24 to 48%, salinity changes -25 to +72%, agricultural costs US$0.9 billion (Beare and Heaney, 2002).
In New Zealand, annual flow from larger rivers with headwaters in the Southern Alps is likely to increase. Proportionately more runoff is very likely from South Island rivers in winter, and less in summer (Woods and Howard-Williams, 2004). This is very likely to provide more water for hydro-electric generation during the winter peak demand period, and reduce dependence on hydro-storage lakes to transfer generation into the next winter. However, industries dependent on irrigation are likely to experience negative effects due to lower water availability in spring and summer, their time of peak demand. Increased drought frequency is very likely in eastern areas, with potential losses in agricultural production. The effects of climate change on flood and drought frequency are virtually certain to be modulated by phases of the ENSO and IPO (McKerchar and Henderson, 2003; see Section 11.2.1). The groundwater aquifer for Auckland City has spare capacity to accommodate recharge under all scenarios examined (Namjou et al., 2005). Base flows in principal streams and springs are very unlikely to be compromised unless many dry years occur in succession.