Metropolitan Melbourne Investigation Discussion Paper - Victorian ...

Figure 2.11
Average annual inflows to Melbourne’s major dams (Thomson, Upper Yarra, O’Shannassy and Maroondah)
from 1913 to 2008
Source: Melbourne Water 2010
— Average infl ow 1913-1996 615GL/Year
— Average infl ow 1997-2009 376GL/Year
1500
GL
1200
Total inflow
900
600
300
0
1913–1922 1923–1932 1933–1942 1943–1952 1953–1962 1963–1972 1973–1982 1983–1992 1993–2002 2003–2009
Year
Increasing temperatures alter wind patterns (atmospheric
circulation) and humidity. A key atmospheric circulation
is the exchange of air from the tropics to mid-latitudes.
A predicted change in this pattern will produce more
erratic rainfall events. 67 In south-eastern Australia, average
annual rainfall, and the number of rainy days are expected
to decrease, however the intensity of rainfall events or
heavy rain storms is likely to increase. Combined with
increasing air temperatures, there will generally be less
surface water and soil moisture. 67,64
Changing rainfall patterns, particularly increased time
between rainfall events and high intensity storm events, is
likely to have negative effects on the natural environment,
water quality, and both sewerage and drainage
infrastructure. Melbourne Water has identifi ed some of the
risks to infrastructure as:
G fl ash fl ooding or damage to sewers and drains,
particularly in coastal environments (see section below),
due to high rainfall events
G pipe failure and collapse due to dry soil conditions
G longer travel times and high concentrations of
sewerage due to reduced fl ow
G decreased surface water and run-off leading to reduced
water quality. 89
River health is also impacted by reductions in rainfall, with
declining river fl ows potentially causing signifi cant changes
in stream conditions and threatening many aquatic or
semi-aquatic species. 88,90
In Melbourne’s catchments, a decrease in infl ow of 7-64
per cent from previous long term averages by 2055 is
modelled for medium emissions growth scenarios. 88 At
the same time increasing population and temperatures are
likely to increase future water demands.
Water conservation and demand management solutions
have been implemented in recognition of current falling
storage levels. In response to these programs and public
campaigns, and despite high temperatures and drought,
Melbourne’s per capita domestic water consumption
has decreased by 34 per cent in 2006/07 compared
to averages of the 1990s; industry has also reduced
consumption by around 38 per cent. 91
48