Australia’s climate in a Four Degree World - Four Degrees of Global Warming - page 10

Three scenarios were defined for each location: 'least hot, wettest', 'mid case'
and 'hottest, driest'. 5 Spatial analogues for the three scenarios were sought based on
current climate matches to the projected annual maximum temperature (tolerance
of  1.0°C) and annual precipitation (  15 per cent) for the target site.
Examples of analogous sites based on climate are shown for Australia's major
cities in Table 2.1 , while Figure 2.7 maps the location of all analogue localities
obtained for selected towns in southern inland agricultural areas.
In the mid and drier cases, there is a clear tendency for Perth, Melbourne,
Adelaide and Canberra to have climates more typical, at present, of the semi-arid
interior. Furthermore, for these two scenarios, inland agricultural sites 'move'
into the arid zone (for instance Dubbo 'moves' to Hermannsburg).
On the other hand, in the least hot, wet case, sites in this zone move towards the
east coast (for example, Nurioopta in the Barossa Valley goes to Muswellbrook in
the Hunter Valley). Melbourne's analogues range from the WA wheat belt in the
driest case through eastern NSW in the wettest case. There is a strong tendency
for the east coast sites of Sydney and Brisbane to adopt climates from at least 1,000
kilometres northwards on the coast (or a little inland in the drier cases).
In some cases, analogues for the new climates of Alice Springs and Cairns can
only be found beyond Australia (see Table 2.1 ). Those for Darwin (not shown)
are unlikely to exist anywhere on the planet.
Perth was assigned analogues in western Queensland, but if a winter rainfall
maximum is maintained (as it should be), it too would have a new climate not
currently present anywhere on earth. Globally, no winter rainfall region is as
warm as Perth is projected to be by the end of this century.
Drought and changes in rates of evaporation
Moisture in the environment is affected not just by changes in rainfall but also
by changes to rates of evaporation. Potential ranges of evaporation have been
recalculated 6 for 1 4°C global warming and presented for each of our selected
localities ( Table 2.1 ) . In all cases, potential evaporation is projected to increase,
with the range being 10 to 20 per cent greater on the east coast and between 0
to 20 per cent greater in the south and inland.
Where average rainfall decreases, drought is likely to increase in frequency,
and this will be exacerbated by the projected increase in potential evapo-
ration. By 2040, exceptionally dry years are likely to occur more often and over
larger areas in the south and south west (i.e. south west of Western Australia
and Victoria and Tasmania regions) (Hennessy et al., 2008a). 7 With greater
relevance to 1 4°C global warming, Kirono et al. (2011) extended this analysis
to 2070 and also included potential evaporation change in a drought index they
used. They show changes in drought frequency in the south and west that ranged
between little change and five times more frequent droughts than current rates.
Changes in the north ranged between a halving and around two to three times
greater occurrence. The implications of these changes for farming and agricul-
tural output are considered in Chapter 6 (Howden et al., 2013).