Metropolitan Melbourne Investigation Discussion Paper - Victorian ...

Reduced rainfall
Melbourne has a highly variable annual rainfall but has
generally enjoyed a long-term reliable average (fi gure
2.10). 66 The long-term average annual rainfall over the
last 150 years recorded in the Melbourne city gauge is
647mm, with a range of 967mm (1916) and 332mm
(1967). 66 Annual rainfall has not exceeded the long-term
annual average since 1996, and despite some good
rainfall in 2010, it is unlikely that this year will see a return
to wetter conditions.
Between 1998 and 2007 the average rainfall across this
region was 14 per cent below the long-term average.
Average infl ows to Melbourne’s major dams (Thomson,
Upper Yarra, O’Shannassy and Maroondah) from 1997 to
2007 were between 30-40 per cent below average (fi gure
2.11). 64,86
Melbourne has experienced a number of periods with
dry conditions or drought generally associated with El
Niño Pacifi c Ocean climatic conditions. In overall terms
the current dry period is similar in some ways to the
period during World War II, but there are very important
differences in seasonal patterns. In particular autumn
changes are outside natural variability as well as there
being generally drier conditions. 87 Melbourne may have
had a step-change in its annual rainfall and stream fl ows
related to climate change. 88 The last 13 years since 1997
constitute the longest period of below average annual
rainfall recorded. 66 Perth, at a similar latitude to Melbourne,
experienced step changes reducing average annual rainfall
on at least two occasions: for the period 1911 to 1974
there are statistically signifi cant reductions over the period
1975 to 1996 and 1997 to 2005.
Figure 2.10
Annual rainfall recorded in central Melbourne from 1856 to 2009 66
Rainfall (mm)
— Median
1000
mm
800
600
400
200
0
1860 1880 1900 1920 1940 1960 1980 2000
Year
47