Chapter 2
Recent trends and projections
on the frequency of extreme weather events
2.1
This chapter examines evidence received by the committee relating to trends
and projections on the frequency and magnitude of extreme weather events,
including drought, bushfires, heatwaves, floods and storm surges.[1]
The focus of the chapter is on trends and projections in the Australian
context, rather than the global context. It also focusses on evidence presented
to the committee during this inquiry: relevant recent reports have been
outlined in the background discussion in Chapter 1.
2.2
This chapter first examines the general concept of 'extreme weather',
followed by general trends and projections on the frequency of extreme weather
events. It then considers in turn the trends and projections in Australia in
relation to particular extreme weather events, including:
- temperature extremes and heatwaves;
-
rainfall extremes, including floods and droughts;
-
bushfires;
- tropical cyclones; and
- storm surges and coastal flooding.
2.3
Finally, this chapter briefly considers the gaps and uncertainties in
relation to those trends and projections, and areas where further research
might be needed.
What is 'extreme weather'?
2.4
Evidence to this inquiry focussed on extreme weather events such as
heatwaves, bushfires, droughts, floods and cyclones. The Intergovernmental
Panel on Climate Change (IPCC) has defined 'extreme weather' as:
The occurrence of a value of a weather or climate variable
above (or below) a threshold value near the upper (or lower) ends of the range
of observed values of the variable.[2]
2.5
The Climate Commission has described an 'extreme weather event' as:
...a weather or climate event which is unusually intense or
long, occasionally beyond what has been experienced before. Examples include
very high (and low) temperatures, very heavy rainfall (and snowfall in cold
climates), and very high wind speeds.[3]
2.6
The Climate Commission has explained that extreme events occur only
rarely, but are noticeable because they are so different from the usual weather
and climate, and are associated with adverse impacts on humans, infrastructure
and ecosystems. It further noted that extreme weather events are often short-lived
abrupt events lasting hours or days—for example, extremely hot days, very heavy
rainfall, hail storms, and tropical cyclones. Other extreme events can last
much longer, such as drought, which is a 'significant lack of rainfall over a
period of months to years'.[4]
2.7
There was some discussion during the committee's inquiry about the
difference between 'weather' and 'climate'. The Climate Commission explains
that 'climate is what you'd expect, and weather is what you get':
Weather is what we get, day to day, which can vary in the
short term. Climate is the long-term average of the weather patterns we
experience, usually taken over 30 years or longer. The long-term average gives
us a sense of what we can expect the weather to be.[5]
2.8
Professor Neville Nicholls summed up the difference as follows:
Climate is in some sense an integration or aggregation of
weather...weather is what we feel; climate is what we expect. It is very
difficult to discern between them...[6]
Trends and projections on the frequency of extreme weather events
General
2.9
It was generally agreed that Australia experiences a highly variable
climate.[7]
For example, the Australian Research Council's (ARC) Centre of Excellence for
Climate System Science submitted that:
There is large year-to-year variability in the frequency of
hot extremes and heavy rain events, heatwaves, droughts and floods across
Australia. These are associated with the natural variability of Australia's
climate, particularly influenced by large-scale phenomena like El Niño-Southern
Oscillation. In eastern Australia El Niño is associated with increased
frequency of droughts, while La Niña is associated with increased frequency of
heavy rain events and flooding.[8]
2.10
While most Australians are probably familiar with the El Niño-Southern
Oscillation, the committee also heard about other natural climate variations that
influence Australia's climate, including the Interdecadal Pacific Oscillation,
which is a pattern of change detected as warm or cool surface waters in the
Pacific Ocean. It shifts phases on a time scale of about 20 to 30 years, and may
affect the occurrence of tropical cyclones.[9]
2.11
However, the committee also heard that the climate is changing due to
human influences, particularly the burning of fossil fuels.[10]
The climate change scenarios put forward by the IPCC and CSIRO show average
global temperature increases from 1 to 5 degrees by 2070, depending on the
level of greenhouse gas emissions.[11]
2.12
CSIRO submitted that:
The natural climate variability that underlies all extreme
weather events is now influenced and altered by the effect of human-induced
warming of the climate system...[12]
2.13
CSIRO further explained that this changing climate will lead 'to changes
in the frequency, intensity, spatial extent, duration, and timing of extreme
weather and climate events'.[13]
2.14
Indeed, the evidence to the committee was that climate change is likely
to increase the frequency and intensity of extreme weather events in the coming
decades.[14]
The Climate Commission reported that:
Climate change is already increasing the intensity and
frequency of many extreme weather events, adversely affecting Australians.
Extreme events occur naturally and weather records are broken from time to
time. However, climate change is influencing these events and record-breaking
weather is becoming more common around the world.[15]
2.15
The committee also heard that climate change will not necessarily be
experienced through gradual trends. Several submitters and witnesses pointed
out that 'small changes in mean climate lead to larger changes in extremes'.[16]
As a result:
Future climate change impacts will increasingly be
experienced first through extreme events rather than gradual changes in mean
temperature or rainfall.[17]
2.16
Dr Andrew Glikson agreed that all the evidence is pointing to an
'accelerating series of extreme weather events around the world' and that:
This is not a gradual trend...When you look at the behaviour of
the atmosphere past and present, it reaches tipping points and from a certain
degree of energy in the atmosphere you get very rapid events over periods
ranging from decades to maybe a century or two.[18]
2.17
Indeed, as outlined in Chapter 1, in recent years Australia has
experienced several notable extreme weather events. The Bureau of Meteorology
(BoM) submitted that:
Long-term observations show that some extreme weather events
are now more common and severe than in the recent past, and model projections
of future climate change indicate that further changes are likely.[19]
2.18
The Bureau of Meteorology informed the committee that providing warnings
for extreme weather events is its 'core business',[20]
and that:
Over the last decade, the Bureau has been particularly active
in issuing severe weather warnings (Figure 1), as Australia has lurched from
record drought to record floods and now to record heatwaves. The intensity of
each of these events is unprecedented. That they should occur in series within
the space of a decade is remarkable.[21]
Figure 2.1: Number
of severe weather-related warnings issued by the Bureau of Meteorology from
July 1997 to June 2012.[22]
2.19
However, the Bureau noted that 'caution is required in inferring trends
in this time series as factors beyond the occurrence of significant weather
events may also contribute to these numbers'.[23]
Extreme temperatures and heatwaves
Trends
2.20
The committee heard that, in general, there has been a trend towards
warmer weather in Australia. In particular, there is an observed trend of more hot
days and hot nights and less cold days and cold nights across Australia in the
last 50 years (see Figure 2.2 below).[24]
Figure 2.2: Trends in indices for
temperatures in Australia over 1951-2010[25]
2.21
Figure 2.2 shows a time series of indices of the number of warm/cool
days (that is, daily maximum temperatures outside the 90th/10th
percentile) and warm/cool nights (that is, daily minimum temperatures outside
the 90th/10th percentile), averaged over Australia for
the period 1951-2010).[26]
2.22
As can be seen from Figure 2.1, the warming trend is more pronounced in
relation to night-time temperatures—that is, 'we are seeing more record-high
minimum temperatures during the night'.[27]
For example, Dr Karl Braganza from the Bureau of Meteorology told the committee
that:
In the last decade we are probably setting records for
night-time temperatures that are warm at about the rate of five to one compared
to cold temperatures. During the day it is about three to one, so
record-setting temperatures we have not seen before across the network are
three times more likely than cold records.[28]
2.23
In terms of heatwaves,[29]
the Bureau of Meteorology submitted that across Australia since the 1950s,
there has been a slight increase in the duration of heatwaves, and an increase
in the maximum temperatures associated with such events.[30]
The Climate Commission has similarly reported that the duration and frequency
of heatwaves increased over the period 1971–2008, and that the hottest days
during heatwaves have become hotter.[31]
2.24
The Bureau of Meteorology noted, however, that there have been:
...marked regional variations in the frequency of occurrence of
heatwaves over that time, with decreases in parts of southern coastal Australia
(especially south-western Western Australia), and strong increases away from
coastal regions. The decreases in heatwave duration across some parts of
southern coastal Australia contrast with increases in the frequency of
single-day high temperature extremes at many of the same locations over the
same period.[32]
2.25
The committee also notes that record temperatures in January 2013 resulted
in the Bureau of Meteorology adding new colours—purple and pink—to its weather
map to denote temperatures once considered off the scale: 50–52°C and 52–54°C
respectively.[33]
Projections
2.26
The trend of increases in the number of hot days and hot nights and
decreases in cold days and cold nights was projected to continue into the
future.[34]
For example, the Bureau of Meteorology predicted that:
It is very likely that the observed trends in the frequency
and magnitude of warm daily temperature extremes will continue and, depending
on emission scenario, potentially accelerate under future global warming. All
regions of Australia are likely to experience significant increases in
temperature extremes in this century.[35]
2.27
These temperature increases are also associated with projections for
increasing frequency and intensity of heatwaves in Australia.[36]
2.28
CSIRO submitted that 'the number of days over 35ºC
is expected to increase significantly by 2030 for many locations in Australia'.[37]
Indeed, the Climate Commission reported that:
...for Adelaide, Melbourne and Canberra the observed annual
number of hot days is increasing more quickly than the climate models
projected. In these cities the annual number of hot days occurring now is at
the level projected for around 2030...[38]
2.29
The Antarctic Climate and Ecosystems Cooperative Research Centre submitted
that its detailed analysis had found that in Tasmania:
Hot summer days and heat waves are projected to increase in
Tasmania in the future. Under a high greenhouse gas emissions scenario the
number of summer days warmer than 25ºC is
projected to double or triple that of the recent climate record. The largest
increases in extreme temperature are projected to be in spring and autumn, with
increases greater than 4ºC leading to a
lengthening of the summer season. Heat waves (three days in a row above 28ºC) are expected to become more frequent – up to
four times more frequent than historical records for Launceston, for example.[39]
Rainfall extremes: floods and
droughts
Trends
2.30
Both the CSIRO and the Bureau of Meteorology submitted that there is
evidence of 'systematic changes in rainfall patterns' in Australia. They
pointed to the following trends in recent decades:
- decreased late autumn and winter rainfall in southern Australia
since the 1980s;
-
increased spring and summer monsoonal rainfall in northern
Australia; and
- a 15% decline in winter rainfall in southwest Western Australia
since the 1970s.[40]
2.31
Professor Will Steffen from the Climate Commission explained that the
likely reason behind the decline in southwest Western Australia is that:
...the rain-bearing fronts off the Southern Ocean that give
south-west WA its rainfall...have slipped southward by a degree or two in
latitude, and that is because of the warming of the climate system; it pushes
the mid-latitude jet streams toward the poles on both sides of the equator.[41]
2.32
The Bureau of Meteorology noted that the 'systematic decline in
autumn-winter rainfall across southern Australia likely exacerbated the severity
of the Millennium Drought'.[42]
2.33
Dr Braganza from the Bureau of Meteorology told the committee that the
reduction of rainfall in the winter months is problematic for water catchments:
It is an important time of the year to lose the rainfall
because it is during that time that we prime the catchment. We get wetter soils
during that period. That allows run-off to occur during the subsequent months
into winter. So the 10 to 20 per cent reduction in rainfall during that time
leads to a 60 per cent reduction in stream flow. You can see that most
obviously in Perth and south-west WA, where catchments are around the 20 per
cent mark.[43]
2.34
Dr Braganza noted that there have also been increases in rainfall
intensity, or heavy rainfall events:
When you go to rainfall intensity—really heavy rainfall
events—in the last three years we have had a lot of records set. We have had
record sea‑surface temperatures around Australia, which is, in some ways,
co‑variable with the rainfall; it influences how much rainfall we get.[44]
2.35
The Climate Commission reported that, while there is considerable
variability in rainfall across Australia, there has been:
- a significant increase in the frequency of heavy rainfall events
in northwest Australia; and
- a slight decrease (not statistically significant) in the number
of heavy rainfall events in southeast and southwest Australia.[45]
Projections
2.36
In general terms, the Bureau of Meteorology submitted that, with global
warming, the planet's hydrological cycle is predicted to intensify, which
essentially means 'more heavy rainfall and more severe droughts'.[46]
The Bureau explained that, as the Earth's atmosphere warms, the amount of
moisture it can hold also increases and that 'this is expected to result in
increases in heavy rainfall events and consequent flooding'.[47]
At the same time, global warming is also expected to increase evaporation,
leading to more severe drought conditions in 'dry' regions of the globe.[48]
2.37
More specifically for Australia, the Bureau of Meteorology explained
that 'changes in Australian rainfall and drought patterns are dependent on
complex changes in the global atmospheric circulation', and warned that there
is uncertainty as to the 'future frequency, timing and spatial extent of those
changes' due to the high variability of rainfall in Australia.[49]
These, and other, uncertainties are discussed in further detail later in this
chapter.
2.38
However, the Bureau of Meteorology submitted that most climate model
projections indicate:
- rainfall decreases in southern and eastern Australia during the
cooler months, particularly in winter and spring;
- increased drought threat for southern Australia as a result of
reduced mean rainfall and higher temperatures; and
- rainfall intensity will likely increase across Australia.[50]
2.39
CSIRO submitted the 'changes in seasonal-average rainfall affect the
incidence of drought and floods'.[51]
So, for example, 'drought occurrence is expected to increase over most of
southern Australia, especially in south-western Australia'.[52]
CSIRO further submitted that modelling in relation to future drought conditions
indicates that:
...by 2030, it is likely...that a 1-in-20 year drought during the
20th century may become a 1-in-10 year drought over south west Western
Australia. By 2050, this could include the Murray-Darling Basin, South
Australia and Victoria, and by 2070 this could extend to eastern New South
Wales and Tasmania. No significant increases in drought frequency are projected
for the northwest WA or northern and central Queensland.[53]
2.40
CSIRO further submitted that climate change projections suggest that
'the Murray-Darling Basin will be on average drier in the future', and that
future droughts in the Murray-Darling Basin may be longer, more frequent and
more severe.[54]
2.41
The Bureau of Meteorology reported less confidence in predicting future
rainfall changes across northern Australia.[55]
However, the Bureau stated that:
[it has] high confidence in projections of warming and
increased atmospheric moisture, and associated increases in heavy rainfall will
likely contribute to a generalised increased flood threat during the tropical
wet season in the future. It is, however, more difficult to predict the future
frequency of severe flooding, due to the inherent, and likely increasing, year
to year variability of Australian rainfall.[56]
2.42
The Climate Commission reported that research indicates that in
Australia:
...it is more likely than not that heavy rainfall events will
become more frequent as the temperature increases...Regionally, increases in
heavy rainfall are expected to be less evident in regions where mean rainfall
is projected to decline...such as southern Australia.[57]
2.43
At the same, the CSIRO submitted that 'increases in extreme daily
rainfall are expected over most of the continent in the future'.[58]
The committee was also advised that there is emerging evidence that high
intensity, short‑duration rainfall bursts, which lead to flash flooding,
may be increasing in intensity.[59]
2.44
In Tasmania, the Antarctic Climate and Ecosystems Cooperative Research
Centre (CRC) noted that it had conducted a detailed analysis of future extreme
events. In relation to rainfall, this analysis found that:
There will [be] more frequent and more intense extreme
rainfall events interspersed with longer dry periods of no rain. It is
projected that there will be an increase of about 25% in the number of days of
extremely high rainfall in both the south west and north east of Tasmania. Peak
intensity rainfall events are projected to increase across Tasmania, leading to
increased flash flooding. Accompanying this increased intensity of rainfall
will be a decrease in the total number of rain days, and thus longer periods
between rain events.[60]
2.45
The centre further noted that extreme and record rainfall events are projected
to become more frequent:
...in some places a 1:200 year event will become a 1:20 year
event. Flooding in the Mersey, Forth and Huon Rivers is expected to increase
significantly.[61]
Bushfires
Trends
2.46
Recent devastating bushfire seasons in Australia have been outlined in
Chapter 1. The committee heard that bushfire danger is likely to increase in
the future, and the bushfire season is likely to be longer, particularly as
result of the projected increases in hot days and droughts.
2.47
The Bureau of Meteorology explained that:
Fire is a natural part of the Australian environment, with
some areas (particularly southern and eastern Australia) being prone to catastrophic
bushfires. Bushfire threat is typically associated with high temperatures, low
humidity, strong winds and high fuel load. Bushfires become catastrophic when
all of these conditions occur in combination...[62]
Projections
2.48
The committee received evidence that the projected increases in hot days
and in consecutive dry days and droughts will lead to increased frequencies of
days with extreme fire danger.[63]
For example, the Australian Academy of Science observed that 'there is a clear
observed association between extreme heat and catastrophic bushfires'.[64]
And that:
A rise of a few degrees in mean temperature would greatly
increase the number of days of extreme heat and extreme or catastrophic
bushfire risk, for example from a few days to tens of days per year in southern
and eastern Australia.[65]
2.49
The Bureau of Meteorology agreed that:
Projected rising temperatures and likely decreases in winter
and spring rainfall across southern Australia...will also contribute to an
increased bushfire threat. In addition, climate modelling shows the potential
for an increase in the frequency of the summer-time weather systems that are
associated with the most extreme and damaging bushfire activity in
south-eastern Australia. However, the change in future fire activity is more
difficult to determine because fire behaviour depends also on fuel type and
accumulation, which may change in the future due to changes in rainfall, fire
frequency and other factors.[66]
2.50
CSIRO noted its projections that warmer and drier conditions are
expected in future over southern and eastern Australia, and that 'consequently,
an increase in fire weather risk is likely, with more days of extreme risk and
a longer fire season'.[67]
2.51
The Conservation Council of Western Australia (CCWA) submitted its
concern that the drying trend in southwest Western Australia will result in
increased risk of bushfire:
...with WA's southern forests becoming more vulnerable to fire
events as they dry out and certain woodland flora (e.g., the Karri forests,
which require average rainfall of over 1250ml a year in order to survive) are
rendered marginal.[68]
2.52
Several submissions also pointed to the annual cumulative Forest Fire
Danger Index (FFDI), which essentially 'sums' daily fire weather danger across
the year. For example, the Bureau of Meteorology noted that the FFDI has
'increased significantly across many Australian locations since the
1970s'[69]
(see Figure 2.2). It was also pointed out that the number of locations with
significant increases is greatest in the southeast of Australia, while the strongest
trends occurred inland rather than near the coast.[70]
Figure 2.3: Trends in annual
cumulative Forest Fire Danger Index[71]
2.53
The ARC Centre of Excellence for Climate System Science explained that:
...in summer rainfall-dominated tropical north-east Australia,
mean and extreme FFDI are projected to decrease or remain close to 20th century
levels;
...in south-east continental Australia, FFDI is projected to
increase strongly by 2100;
...the fire season is projected to start earlier in [south-east
Australia], potentially leading to a longer overall fire season.[72]
2.54
Several submissions noted that the largest increases in seasonal FFDI
have occurred during spring and autumn, which indicates a longer fire season.[73]
2.55
The committee also heard that, following the Black Saturday bushfires in
Victoria, a new fire risk category of 'catastrophic' had been added to fire
danger indicators to allow for conditions that were 'off the record'.[74]
Tropical cyclones
Trends
2.56
Tropical cyclones are defined as:
...low pressure systems that form over warm, tropical waters
and have gale force winds (sustained winds of 63km/h or greater and gusts in
excess of 90km/h near the centre)... The gale force winds can extend hundreds
of kilometres from the cyclone centre.[75]
2.57
The Bureau of Meteorology reported that, on average, the Australian
region experiences about 11 tropical cyclones per year, but the number varies
significantly from year to year.[76]
2.58
The committee heard that there is no evidence of significant trends in
the total numbers of tropical cyclones in the Australian region.[77]
In particular, the Bureau of Meteorology submitted that the 'relatively short
time span of consistent records, combined with high year-to-year variability,
makes it difficult to discern any clear trends in tropical cyclone frequency or
intensity for the Australian region'.[78]
2.59
On the other hand, Mr Jeff Callaghan from Green Cross Australia observed
that tropical cyclones in Queensland are affected by multi-decadal cycles such
as the Interdecadal Pacific Oscillation, and that the second half of the 19th
century was a much more active period for cyclones than the 20th
century.[79]
Projections
2.60
Noting the problems with lack of reliable long-term records for cyclones
in Australia, the general consensus in evidence to the committee was that
cyclones are likely to be more intense in the future, but there is unlikely to
be an increase in the overall number of cyclones. For example, Professor
Steffen from the Climate Commission told the committee that:
In principle, we are going to see a change in cyclone
behaviour, and that is pretty obvious because the sea surface temperature is
rising. This means there is more energy in those surface waters, and that is
where cyclones draw their energy from. However, the interesting thing is that
it looks like we will not have more cyclones—in fact we will either have about
the same or perhaps a little fewer...but, on balance, they are going to be more
intense when they do occur.[80]
2.61
It was explained that the reason cyclones will be more 'intense' is
because the wind speeds will be higher and there will be more rainfall.[81]
In terms of the frequency of cyclones, the Climate Commission has explained:
...the vertical gradient in temperature through the atmosphere,
that is, the difference between the temperature near the surface of the Earth
and the temperature higher up in the atmosphere, is likely to decrease as the
atmosphere continues to warm. The formation of tropical cyclones most readily
occurs when there are very warm conditions at the ocean surface and when the
vertical gradient is strong. As the vertical gradient weakens, it is likely
that fewer tropical cyclones will form.[82]
2.62
The Bureau of Meteorology similarly submitted that global climate change
projections indicate that 'there will be less tropical cyclones in overall
number', but a greater number of particularly intense cyclones. It noted that
'this is consistent with recent findings for the Australian region'.[83]
2.63
CSIRO agreed that tropical cyclones in northern Australia 'are likely to
become more intense with a decrease in frequency'.[84]
CSIRO also noted that sea‑surface temperatures are important for cyclone
formation, and that sea-surface temperatures have 'been at or near record high
values off the western Australian coast in recent years'.[85]
CSIRO also noted that the modelling projections indicate southward movement of
around 100km in the 'decay' region of cyclones (the region into which weakened
tropical cyclones migrate).[86]
However, Dr Stafford Smith from CSIRO warned that there is a lot of uncertainty
as to whether cyclones will move further south.[87]
2.64
At the same time, Insurance Australia Group told the committee that
research by its dedicated meteorology team indicated that over the next 50
years, 'the number of the most destructive category 4 and 5 tropical cyclones
forming in waters off Eastern Australia could increase and track further south'.[88]
2.65
The committee was told it is difficult to make projections in relation
to thunderstorms, because they tend to be very localised.[89]
At the same time, Insurance Australia Group submitted that its research into
the future climate impacts of severe hail storms in the Sydney region indicated
that there could be 'a doubling of hailstorms with hailstones greater than 10
centimetres in diameter in the greater Sydney region over the next 50 years'.[90]
Storm surges and coastal flooding
Trends
2.66
The committee heard that rising sea levels are likely to cause damage to
coastlines by exacerbating coastal flooding and erosion from storm surges and
cyclones.
2.67
The Bureau of Meteorology submitted that average sea level globally has
risen by around 21cm in total over the last century, and that the rate of sea
level rise is now around 3.1mm per year (see Figure 2.4).[91]
Figure 2.4: Global average mean sea
level: 1880 to 2011[92]
2.68
The Bureau of Meteorology noted that the projection is for a further
average global sea level rise of between 18 and 59 cm by the end of this
century, with the eventual rise depending upon the future emissions.[93]
It was explained that this sea level rise is due to the expansion of ocean
water as it warms, and the addition of new water from the melting of land‑based
ice such as glaciers and ice sheets.[94]
2.69
Around Australia, the observed sea level rise is slightly greater than
the global average, although there is considerable variation around the
Australian continent. The Bureau of Meteorology noted that rates of sea level
rise in northern Australia are amongst the highest in the world, with current
rates up to 1 cm rise per year (see Figure 2.5).[95]
Figure 2.5: The rate of sea-level
rise around Australia from January 1993 to December 2011[96]
2.70
As Professor Steffen from the Climate Commission noted:
Around the Top End, the rate of sea level rise in Australia
is about three times the global average. The Southern Ocean, along the southern
coast of Australia, is less than the global average. Around the east coast, it
is about the global average.[97]
2.71
Professor Steffen told the committee that 'one of the most certain
aspects of climate change is that sea levels are going to rise', but 'there is
a lot of uncertainty about how much sea level is going to rise'.[98]
He explained that:
...there is already a lot of heat in the ocean that has not
worked its way through the system yet. The water is still expanding in response
to that. And then on top of that is we are starting now to get additional water
flowing into the ocean from melting glaciers and ice caps.[99]
2.72
The committee heard that rising sea levels will exacerbate coastal
flooding and erosion from 'storm surges'. A 'storm surge' is:
...a rise above the normal sea level resulting from strong
onshore winds and/or reduced atmospheric pressure. Storm surges accompany
tropical cyclones as they make landfall but can also be formed by intense low‑pressure
systems in non-tropical areas, such as 'East Coast Lows' in the Tasman Sea.[100]
2.73
Storm surges can cause extensive flooding of coastal areas, and are
worst when they coincide with a particularly high tide.[101]
Submitters explained that higher sea levels will amplify the effects of storm
surges:
The frequency and impacts of coastal flooding from extreme
events such as storm surges will be significantly amplified by sea level rise,
because the surges take place on a higher background sea level.[102]
2.74
The Bureau of Meteorology submitted that 'it has been estimated that an
average sea-level rise of 50 cm will result in a 10-1000 times increase in the
frequency of coastal flooding depending on the particular location around the
Australian coastline'[103]
(see Figure 2.6).
Figure 2.6: Projected increase in
frequency of flooding events from the sea
for a sea-level rise of 0.5m[104]
2.75
CSIRO similarly explained that a sea-level rise of 50 cm might mean
that:
Extreme events that now happen every 10 years, on average,
would happen about every 10 days in 2100, and become even more frequent around
Sydney, with smaller increases around Adelaide and along parts of the Western
Australian coast.[105]
2.76
Professor Steffen noted that these effects are already being observed in
areas with reliable records, such as Fremantle and Fort Denison in Sydney,
where there has been about a threefold increase in flooding events since 1950.[106]
The Climate Commission has also reported that the Torres Strait Islands are
also increasingly vulnerable to flooding as a result of increases in sea levels.[107]
2.77
Another concern related to the increased risk of severe coastal flooding
events where coastal settlements are inundated by water from both seaward and
landward directions. That is, where there is a combined impact from:
(i) the combination of storm surge, a high tide and a higher sea level, and
(ii) flooding rivers from the catchments behind the settlements.[108]
2.78
For example, the Climate Commission noted that:
Little research has yet been done to connect these two
phenomena and produce an overall change in risk factor for this type of 'double
whammy' coastal flooding event. However, the rises in sea level over the 21st
century, which are virtually certain, coupled with the projections of a modest
increase in the frequency of heavy rainfall events for southern Australia suggest
that the risk of these 'double whammy' flooding events will increase.[109]
2.79
The Bureau of Meteorology also submitted that, due to higher sea levels,
weak to moderate strength tropical cyclones will be likely to generate more
coastal flooding than at present, and severe cyclones are more likely to result
in very serious damage to coastlines through flooding and erosion associated
with storm surges.[110]
2.80
The committee heard concerns about the impacts of sea level rise in
certain states. For example, in Tasmania, analysis of future extreme weather
events found that an increase in mean sea level of between 5 and 14 cm by 2030
will lead to:
...1:100 year storm tide events doubling in frequency. By the
end of the 21st century the 1:100 storm tide is projected to be an annual event
for higher emissions scenarios...The addition of more intense rainfall events
will exacerbate the impacts of sea-level rise on flooding in rivers (and vice versa).[111]
2.81
The Northern Territory Police, Fire and Emergency Services advised that
they had done some storm surge mapping of the Darwin area which took into
account probable sea level rises over the next 50 to 100 years. This mapping
indicated that some remote communities may 'go under in a big storm surge event
... [but] the effect on Darwin is not really that great'.[112]
Uncertainties in future projections
2.82
There was some discussion during the committee's inquiry about
uncertainty in terms of projections of future extreme weather events. However, little
uncertainty was expressed about the fact that the climate is changing, and that
these changes are being influenced by anthropogenic forces. For example,
Dr Glikson told the committee that 'ninety-five point five per cent of the
peer-reviewed literature on which the science is based agrees about the effect
of greenhouse gases'.[113]
2.83
CSIRO submitted that the two main areas of uncertainty relating to the
projections of future climate are:
...the level of humanity's future greenhouse gas and aerosol
emissions; and the response of the Earth's climate system to those emissions.
These uncertain factors will affect the speed and extent of expected climate
change.[114]
2.84
The Bureau of Meteorology agreed that the rate and magnitude of future
changes to climate will be determined by the future level of greenhouse gas
emissions, 'and a series of complex environmental feedbacks'.[115]
2.85
The committee heard that there is uncertainty about the specific impacts
of climate change—that is, 'how will extreme events change: where will they
change, when will they change and what will be the combination'?[116]
2.86
Dr Stafford Smith from the CSIRO told the committee that:
...the details of future climate change are often perceived as
imponderably uncertain, but in reality we have got very high confidence that change
is actually happening. Indeed, some variables such as rising temperature
extremes are much more certain for the future than others, and even for the
ones which are less certain there are a whole range of risk mitigation
approaches which are widely used in society in other contexts which are
appropriate for different sorts of uncertainty.[117]
2.87
The committee was told that the IPCC uses standard terminology to communicate
the degree of uncertainty in its projections of the impacts of climate change.[118]
For example, the level of confidence in the evidence is expressed using the
qualifiers 'very low, low, medium, high and very high'.[119]
The likelihood of a particular outcome is expressed in terms of probability as
set out in Table 2.1 below.
Table 2.1: Terms used by the IPCC
to indicate the assessed likelihood[120]
|
Term
|
Likelihood of the outcome
|
|
Virtually certain
|
99-100% probability
|
|
Very likely
|
90-100% probability
|
|
Likely
|
66-100% probability
|
|
About as likely
|
33-66% probability
|
|
Unlikely
|
0-33% probability
|
|
Very unlikely
|
0-10% probability
|
|
Exceptionally unlikely
|
0-1% probability
|
2.88
So the IPCC has stated that, for example:
-
It is virtually certain that increases in the frequency
and magnitude of warm daily temperature extremes and decreases in cold extremes
will occur in the 21st century at the global scale;
-
It is very likely that the length, frequency, and/or
intensity of warm spells or heat waves will increase over most land areas;...
-
It is likely that the frequency of heavy precipitation or
the proportion of total rainfall from heavy falls will increase in the 21st
century over many areas of the globe;...
-
there is medium confidence that droughts will intensify in
the 21st century in some seasons and areas, due to reduced precipitation and/or
increased evapotranspiration;...
-
it is very likely that mean sea level rise will contribute
to upward trends in extreme coastal high water levels in the future; [and]
-
There is high confidence that locations currently
experiencing adverse impacts such as coastal erosion and inundation will
continue to do so in the future due to increasing sea levels, all other
contributing factors being equal.[121]
2.89
Professor Nicholls explained that:
We are confident, for instance, that a hot day that occurs
only about once every 20 years currently will occur about every year or two by
the end of the century in most parts of the world. On the other hand, although
heavy rainfall days are expected to become more frequent and heavier, the
magnitude of the change is expected to be much less than for temperature. We
are also less confident about this rainfall projection. The actual increase may
be substantially more or less than our current expectation. These uncertainties
can complicate the development of ways to adapt to our changing climate.[122]
2.90
In terms of projections for Australia, the committee heard that the
level of confidence also varies depending on the particular climate variable.
For example, the general consensus before the committee was that there is a
high degree of confidence in the projections about temperatures, but less
confidence in rainfall.[123]
In particular, uncertainty was expressed about whether 'flood risk will
increase or decrease in the majority of Australia'.[124]
Similarly, there is some uncertainty about the future frequency and intensity of
tropical cyclones in Australia.[125]
2.91
The uncertainty in the area of rainfall was attributed to higher natural
variability in rainfall in Australia due to influences such as the El Niño Southern Oscillation.[126]
The committee was told that climate models 'do not currently realistically
simulate' these natural cycles.[127]
Areas needing more research and
analysis
2.92
The committee heard that there are areas where the knowledge and data is
good, while other areas need further research and analysis.
2.93
In terms of collection of information and observations about weather,
the committee was told that Australia generally has very good temperature
records, rainfall measurements, and sea level records going back 100 years in
places.[128]
For example, Dr Neville Smith of the Bureau of Meteorology described
Australia's climate records as 'pretty sound and robust, though perhaps not to
the detail that we want in some regions'.[129]
He also stated that Australia has 'both world-class weather forecast models and
world‑class climate models'.[130]
2.94
Several submitters and witnesses emphasised the need for continued
support for the work of existing organisations such as the Bureau of Meteorology,
CSIRO, and the Bushfire CRC. For example, witnesses welcomed the work of the
Bushfire CRC in relation to bushfires, and the recent announcement of $47
million in funding to turn the Bushfire CRC into the Bushfire and Natural
Hazards CRC.[131]
Similarly, the Australian Meteorological and Oceanographic Society submitted
that:
Long-term, consistent, high-quality sets of observed climate
are critical to the detection of climate change. Many of these observations are
derived from the Bureau of Meteorology's routing observing network. Australia
is a world leader in the development of such data sets but their continuation
is dependent on the existence of a high-standard observations network,
and the availability of adequate resources to maintain that network at a
high standard.[132]
2.95
The Wentworth Group of Scientists told the committee that:
We should harness the high-quality science that this country
has invested in over many years to improve our emergency response capabilities
to manage extreme weather by improving our capability to predict and monitor
the movement and intensity of these weather systems in real time, whether it be
droughts, cyclones, bushfires, floods or storm surges.[133]
2.96
Professor Nicholls expressed the view that improved weather forecasts are
a good way to reduce the deleterious impacts of weather and climate extremes.[134]
Similarly, the Bureau of Meteorology submitted that:
Early warning systems have proven time and time again to be
the most effective and cost efficient approach to mitigating economic losses
and loss of life arising from severe weather.[135]
2.97
The committee notes that the Commonwealth government recently conducted
an independent review on the Bureau of Meteorology's capacity to respond to
future extreme weather and natural disaster events and to provide seasonal
forecasting services. That review made a number of recommendations including,
for example, the need to improve the arrangements for flood monitoring,
forecasting and warning across Australia. The Bureau noted that 'the government
is currently giving consideration to the recommendations of this review'.[136]
The Bureau also noted in its submission that there are coordination issues in
relation to flood river level monitoring, and also flash flood warnings.[137]
This is discussed further in Chapter 5.
2.98
The committee heard that there are some areas needing further research. For
example, the committee heard that there is a gap in knowledge when it comes to
predicting cyclones in Australia. For example, Australian records for tropical cyclones
rely on satellites which only go back to the seventies and eighties, and
therefore there is only a small sample size.[138]
So, for example, WWF-Australia and the Northern Territory emergency services expressed
the view that 'more research is required to reduce the levels of uncertainty'
around the projections in relation to tropical cyclones in Australia.[139]
Mr Peter Davies of the Northern Territory Police, Fire and Emergency Services
told the committee that many of the models being used to predict the impact of
climate change are based on American models of cyclones that haven't been
tested in the Australian environment.[140]
2.99
Similarly, Insurance Australia Group submitted that:
...there are extremely few measurements of the
intensity/central pressure, eye size and radius of storm force winds and storm
surges of tropical cyclones, despite their potential to inflict extreme damage
on communities near their paths. In the USA there is a routine program of
aerial reconnaissance to quantify the physical size and intensity of these
systems but there is no similar program in Australia.[141]
2.100
However, the committee heard cyclone prediction has improved in recent
years due to advances in computing. Dr Smith from the Bureau of Meteorology
provided some recent examples:
If you took us back 10 years, we could not have given the
forecast for tropical cyclone Yasi, simply because we did not have the
computers. Now both we and other weather agencies have the ability to do
tropical cyclone Yasi—and Rusty was the most recent example, off the North-West
Gulf—five or even seven days out.[142]
2.101
Further improvements to supercomputing power would allow for high
resolution analysis and could improve forecasting of extreme weather events.
Such analysis would focus on:
the probabilities; ... the spread of possible outcomes, so you
can start to give some guidance about the likelihood that a certain community
might be impacted more heavily or less heavily than another community.[143]
2.102
Indeed, several submitters and witnesses, particularly local government
associations, expressed a desire for more work to be done to provide data and projections
for climate change and extreme weather events at a local level.[144]
For example, the Australian Conservation Foundation (ACF) submitted that:
Extreme weather events are geographically specific, and not
consistent across the nation or even within any one state. Wherever possible,
extreme weather trends need to be as granular as possible. Specific sea level
inundation assessments for vulnerable cities such as Cairns are good examples
of local, specific extreme weather assessments. This level of specificity is
not found across the nation and across the spectrum of extreme weather types.[145]
2.103
Dr Smith from the Bureau of Meteorology told the committee that to get
forecasting to a more local level:
[It] just comes down to resolution—how many grid points you
can put in your model, and that just depends on the size of the supercomputer.
So there is a decision we have to make with government about
how much investment we should put in supercomputing versus the return we get by
being able to have higher resolution...[146]
2.104
At the same time, the committee heard that work is being done to provide
forecasts and projections at regional and local levels.[147]
For example, the Australian Meteorological and Oceanographic Society noted that
a number of regional assessments of climate change impacts have been produced,
including:
- the Indian Ocean Climate Initiative (for Western Australia);[148]
- Climate Futures for Tasmania;[149]
and
- the South-Eastern Australian Climate Initiative.[150]
2.105
However, the Australian Meteorological and Oceanographic Society noted
that:
Neither IOCI nor SEACI, which were both joint projects
involving various Commonwealth and State agencies, have received ongoing
funding and both have been, or are in the process of being, wound up, which is
a concern for the future availability of regionally-specific assessments.[151]
2.106
In terms of regional and local projections, the Griffith Centre for
Coastal Management submitted information about its research project to produce
a pilot real-time storm surge forecasting system for Queensland.[152]
They identified a number of constraints and actions that would improve the
accuracy of such forecasting, including improvements to data availability and
collection in terms of bathymetry,[153]
wind, wave and water level measurements; and further research into the dynamics
of storm surge propagation through the Great Barrier Reef.[154]
For example, the Griffith Centre suggested that 'Australia's network of storm
tide gauges is sparse relative to the length of coastline and the expanding
vulnerable population'.[155]
2.107
However, the committee notes that the Queensland government reported
that Queensland has 25 fully operational storm surge monitoring gauges.[156]
2.108
Others gaps in Australia's observation network were also identified. For
example, Dr Todd Lane from the Australian Meteorological and Oceanographic
Society noted that there are gaps in Australia's radar network:
The Bureau of Meteorology have expanded their radar network
considerably in recent years and are still expanding the network, but along the
coastlines there are still gaps in coverage. There are places in Far North
Queensland which do not receive any radar coverage at all and parts of the
Northern Territory as well. There are these sizeable gaps in the radar network
when you compare it to other countries. The UK is entirely covered by radar. In
the US there are only a couple of small gaps around the country. But Australia
has some very large gaps. If we are talking about major investment in
infrastructure for detecting flooding rains, radar could be one of those
things.[157]
2.109
The committee also heard that more research is needed on the interaction
between human-induced climate change and large-scale natural climate
variations, such as the El Niño/Southern Oscillation and the Pacific Decadal
Oscillation/ Interdecadal Pacific Oscillation.[158]
Others emphasised the need for more research in the area of rainfall and the
drivers of floods and drought. For example, Dr Anthony Kiem told the
committee that research funding is needed to increase understanding of 'the
drivers of flood and drought risk in Australia...especially at the local or
catchment scale'.[159]
Others agreed that:
There is currently a lack of substantive research into
understanding how the interaction of likely increases in flood-producing
rainfall and the net drying of catchments will increase future flood risk...[160]
2.110
In terms of rainfall records, Dr Blair Trewin from the Australian
Meteorological and Oceanographic Society informed the committee that:
For remoter areas, records are often short term and, perhaps
surprisingly, some of the coastal areas are not as good for rainfall records as
they could be—sites have moved around and that sort of thing.[161]
2.111
The Australian Meteorological and Oceanographic Society suggested that
'the potential exists to reduce such data voids through the strategic opening
of new stations'.[162]
Others identified a need for more rain gauges to help predict flash flood
warnings.[163]
2.112
Insurance Australia Group called for more work in the area of storm
surges:
...the threat of storm surge for most parts of Australia has
been limited to simple sea level rise scenarios rather than taking into account
potential changes in the weather systems likely to produce a storm surge and
the detailed bathymetry and coastal zone features that will modify and, in some
cases, increase the threat of storm surge in coastal regions.
There is a need to more accurately quantify the risks facing
properties in coastal and estuarine regions, particularly in locations where
there is a merging of the riverine floods with coastal storm surge effects.[164]
2.113
Insurance Australia Group further noted that there has been 'no thorough
investigations into likely changes in the distribution or seasonality of severe
storms in the future' and that:
This research, with the involvement of the insurance
industry, is very important if our major urban centres are to be made more
resilient to the impacts of these storms in the future.[165]
Committee comment
2.114
The committee recognises the evidence that climate change is likely to
increase the frequency and intensity of extreme weather events in the coming
decades. The committee also recognises the fundamental importance of being able
to predict and monitor extreme weather to enable us to manage and improve our
capability to respond to future extreme weather events. In this respect, the
committee commends organisations such as the Bureau of Meteorology and CSIRO
for their excellent work in this area. The committee considers that this work
is fundamental to Australia's future planning to manage extreme weather events
and in relative terms Australia is very well served by the extent of work
already undertaken. The committee therefore recommends that the Commonwealth
government, through the Bureau of Meteorology and CSIRO, continue to support
data collection and research to improve forecasting of extreme weather events,
especially early warning capabilities.
Recommendation 1
2.115
The committee recommends that the Commonwealth government, through the
Bureau of Meteorology and CSIRO, continues to support data collection and
research to improve forecasting of extreme weather events, especially early
warning capabilities.
2.116
The committee also heard that there is a need for more data and research
to make predictions at a more local level for future planning purposes. On
that basis, the committee recommends that the Bureau of Meteorology and CSIRO
continue their work to improve projections and forecasts of extreme weather
events at a more local level, especially in relation to events such as flooding
or storm surges.
Recommendation 2
2.117
The committee recommends that the Bureau of Meteorology and CSIRO
continue to improve projections and forecasts of extreme weather events at a
more local level.
2.118
The committee notes that a number of areas for further research were
identified during the course of the committee's inquiry. In particular, the
committee acknowledges that there is a need to conduct further research to
improve understanding of the interaction between large-scale natural climate
variations, climate change and extreme weather events.
The committee recognises that there are areas where there is a
high degree of confidence in the projections of future extreme weather,
particularly in relation to future temperatures. However, there are other areas
where there is less confidence and further research is needed, particularly in
relation to changes to future rainfall patterns and the associated floods and
droughts. There is also uncertainty in relation to the implications of climate
change for tropical cyclones in Australia. The committee therefore recommends
that the Bureau of Meteorology and CSIRO conduct further research to increase
understanding in these areas and that Australia cooperatively engage, where
appropriate, with international research initiatives in these areas.
Recommendation 3
2.119
The committee notes the linkage between climate change and extreme
weather events and recommends that the Bureau of Meteorology and CSIRO conduct
further research to increase understanding in the areas of:
- the interaction between large-scale natural variations, climate
change and extreme weather events;
- the impacts of climate change on rainfall patterns and tropical
cyclones; and
- that Australia cooperatively engage, where appropriate, with
international research initiatives in these areas.
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