Hot in the city - Four Degrees of Global Warming - page 158

10 Hot in the city
Planning for climate change impacts in
urban Australia
Jan McDonald
Introduction
Australia's climate is already changing as a result of human influence. Over the
past 50 years, we have experienced increased average and maximum tempera-
tures, decreases in daily minimum temperatures, a 10-40 per cent increase in fire
weather, and drying trends across the south west and south east ( Chapters 2 and
3 , Hennessy et al., 2005; BoM and CSIRO 2007).
With four degrees of warming, the number of extreme heat days (days over
35°C) in Australian cities will increase dramatically, from 3.5 to 12 days in
Sydney, 9 to 26 days in Melbourne, 28 to 67 days in Perth, 1 to 21 days in
Brisbane and 11 to 308 days in Darwin (Braganza et al., 2013 [ ch. 3 , this volume];
CSIRO and BoM, 2007). Rainfall and severe hail events are expected to intensify
(CSIRO and BoM 2007; Rafter and Abbs 2009) and the number of extreme fire
danger days for a projected 2.9°C warming is expected to increase by between 100
and 300 per cent (CSIRO & BoM 2007; Braganza et al., 2013, ch. 3 , this volume).
The frequency of cyclone activity is projected to decrease, although the intensity
of such events is likely to increase (Whetton et al., 201, ch. 2 , this volume).
The IPCC projections of sea level rise for 2-5.4°C of global warming are
conservatively in the range of 23-51cm by 2100 (IPCC, 2007). Even small rises
in sea level will greatly shorten the average recurrence interval (ARI) for coastal
inundation events (Australian Government, 2009). For example, a sea level rise
of 20cm would reduce the ARI for what is currently a 1-in-100 year storm surge
in south-east Queensland to 61 years. The interval drops to just 9 years with a
rise of 1 metre (Wang et al., 2010).
It is trite but perhaps salutary to point out that, in Australia, these climate
change impacts will take effect in conjunction with population growth and
movement and other demographic change. A severe cyclone will cause less
property damage in a sparsely developed area than in a densely populated city,
although impacts on biodiversity and natural values or other economically
valuable industries may be significant. The severity of impacts will also be
mediated by what adaptation measures have been implemented: drought will
be less disruptive to urban populations that have already reduced their water
consumption or improved water storage and supply.