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4. Climate Change Projections
The following analysis provides a snapshot of the Study Area’s historical climate and of how this may
change in response to climate change. The analysis uses observations from the Bureau of Meteorology
(BoM) to provide an insight into the region’s historical climate. Outputs from climate change modelling
undertaken for the Intergovernmental Panel on Climate Change’s (IPCC’s)
Fourth Assessment
Report
(IPCC, 2007) are then used to explore how the West Adelaide region’s climate may change in future.
This information provides the basis for assessing climate change vulnerability and risks throughout the
Study Area and for developing adaptive responses.
4.1.
Drivers of Regional Climatic Variability
Year-to-year variations in sea surface temperatures (SSTs) in both the Indian and Pacific Oceans and
variations in atmospheric circulation exert powerful influences on Australia’s climate (
Figure 4.1
). The El
Niño and La Niña phases of the
El Niño-Southern Oscillation
(ENSO) are associated with contrasting
patterns of rainfall and air temperature in eastern Australia. In particular, the warm El Niño phase of
ENSO is associated with marked reductions in rainfall and increased air temperatures, while cool La Niña
events are typically associated with enhanced rainfall and cooler air temperatures (e.g. Kiem and Franks,
2001; Verdon
et al
., 2004).
SST fluctuations in the Indian Ocean (related to the
Indian Ocean Dipole
, IOD) have similar influences
and are correlated with rainfall variability in both western and south-eastern Australia (e.g. Verdon and
Franks, 2005). The Inter-decadal Pacific Oscillation (IPO) plays an important role in modulating rainfall
and streamflow variability in eastern Australia over multi-decadal timescales (e.g. Power
et al
. 1999;
Verdon
et al
. 2004). The IPO appears to influence both the strength and nature of the ENSO cycle and
modulate the frequency of individual ENSO events. The Southern Annular Mode (SAM) controls the
passage of westerlies and embedded frontal weather systems across the Southern Ocean. Its modes
influence the latitude of these weather systems, which bring rain to southern Australia.
These phenomena contribute to the significant inter-annual variability in climate and recurring drought
cycles experienced in south-eastern Australia. Several major droughts have been recorded over the last
150 year: the Federation drought of 1895-1902; the World War II era drought of 1937-1945; and the
Millennium drought of the 2000s (2000-2008). The character of each of these has varied (Verdon-Kidd
and Kiem, 2009). The Millennium drought was predominantly driven by El Niño and resulted in large
reductions in rainfall during spring and summer in eastern Australia. During the World War II drought, an
extended dry phase in Pacific, Indian and Southern Oceans produced a drought with below average
rainfall in all seasons and across most of the continent. While El Niño contributed to the most recent
drought, La Niña events relieved drought conditions in parts of north-eastern Australia and warm
conditions in the Indian Ocean meant that north-western Australia experienced wetter than average
conditions. However, rain from these events did not reach south-eastern Australia due to the blocking
effect of SAM (Verdon-Kidd and Kiem, 2009).
