projections.2 This is because the effects of mitigation become evident mostly
after 2050.
Second, assuming the validity of the median projections used here, mitigation
leading to stabilization of global CO2 at 450 ppm is sufficient, in combination
with adaptation, to reduce economic damage from climate change to modest
levels (less than $400 million year). By contrast, while adaptation alone is a
reasonably effective response for the period from now until 2050, it becomes
ineffectual when inflows fall sharply as projected for the second half of this
century.
Third, salinity can be managed to achieve the current policy target of a
maximum of 800 EC for Adelaide water supply in all simulations except the
‘adaptation only’ simulation for 2100. For this simulation, the failure of runoff in
the drought state of nature makes the hydrological component of the model
unreliable by 2100. Subject to the obvious uncertainties involved with such a
long period, the projections imply that the Darling river will become a closed
system with no net outflow. In Drought states, the Murray and Murrumbidgee
become a series of ponds, and no longer provide sufficient water for Adelaide
potable drinking supplies. With the exception of some upstream catchments, the
modelling results reported for this case involve the replacement of irrigation by
dryland agriculture.
Finally, comparison of the baseline simulation with the ‘mitigation and
adaptation (environment has priority)’ simulation shows that it is possible to
maintain existing environmental flows at a cost of around $250 million/year,
assuming global mitigation policies are successful. Given that the Australian
government has committed $10 billion over 10 years to the National Water Plan,
2 These results are derived from median projections of climate change. Within the range of model
projections consistent with our current knowledge, ‘hot dry’ variants show substantial effects on
flows, outputs and economic returns before 2050.
20