Transcript Climate Variability and Trends in Australia David Walland Bureau of Meteorology Carbon-Drought Workshop 5-8 June Canberra.

Climate Variability and Trends
in Australia
David Walland
Bureau of Meteorology
Carbon-Drought Workshop
5-8 June
Canberra
Outline
• An introduction to Australian
climate (rainfall) variability
• The emergence of climate change
amongst the variability
• Projections
A Long History of Rainfall
Variability
Australia is unique amongst developed countries. Natural and
human systems must be adapted to a boom bust climate
Variability of Annual rainfall
(100 years of data for Australia and generally also for the other countries)
20
18
16
Coefficient (%)
•
14
12
10
8
6
4
2
0
Australia S. Africa Germany France
NZ
India
Country
UK
Canada
China
USA
Russia
Australian Rainfall - Droughts
and Deluge
Impact on Biosphere
• Droughts clearly impact on water limited
vegetation e.g. tree mortality (Breshears et al
2005), crop yield etc.
• Bushfires have a major impact on all types of
vegetation
– Drought associated with the lead up to the 2002/03
bushfires
– Extreme event to trigger fires e.g. Wilsons Prom
bushfires (April 2005 was nationally hottest April on
record (largest temp anomaly on record) & fires
occured during a record breaking heatwave)
Significant drivers of Rainfall
Variability
• Natural variability in Australian rainfall is
due to many factors, some chaotic.
• El Nino is one of the more dominant
predictable influences.
• 1998-99 and 2002-03 were La Nina and El
Nino years respectively.
The Walker Circulation - “normal” and El Nino
Annual Rainfall For Australia
800
750
Emerging
Climate Trends
5 Year Mean
Rainfall (mm)
700
650
600
550
500
450
High-quality rainfall dataset:
Annual trends
400
350
300
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Year
High-Quality Annual
Temperature
• 1910-2005 trends:
• Max T: +0.06°C/decade
• Min T: +0.12°C/decade
Impact of Extremes
• systems have adaptive capacity so they may be
stressed but can often cope with slow changes in
the mean
• extremes events can exceed their adaptive capacity
and tip the system over the edge e.g.
– hot days …. Bushfires
– Tropical cyclones ….wind damage, saltwater intrusion
• there is much on-going research into frequency of
extreme events
High-quality Daily
Temperature: Daily
Extremes
Average number of Hot Days/Nights and Cold Days/Nights
140
Hot Days: Max T ≥
35oC
No. per year
120
100
Cold Days: Max T ≤
15oC
80
60
Hot Nights: Min T ≥
20oC
40
20
0
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
Year
• Shifts consistent with changes in mean
• Averaged over “valid” regions only
• Updated from Collins et al. (2000)
2005
Cold Nights: Min T ≤
5oC
Sea Surface
Temperature Trends
Smith and Reynolds (2004)
• Free from urban
influence, show
rapid warming
about SE
Australia =>
interesting
insight into the
synoptic
changes
El-Nino
• Walker Circulation has been
observed to be weaker over the
past century which implied a more
El Nino like state in the Pacific.
– Consistent with observed rainfall
trends
• No consensus about the future
evolution and whether this scenario
is likely to continue.
Changing weather systems
& rainfall
Reductions in Southern Australian rainfall are likely due to changes
in the dominant weather systems themselves.
A southward shift in the
frontal/low pressure
system genesis region
would have a huge
impact on Southern
Australia
Such a change has been
mechanically linked to
increases in greenhouse
gases and reductions in
polar ozone.
Impacts on water resources
South-coastal April-July Rainfall (mm)
Southern
Australian early winter
Rainfall (mm)
400
y = -0.9275x + 2083.3
R2 = 0.0798
Rainfall (mm)
350
1000000
300
Total capacity is 1.770 GL
900000
250
Series1
Linear (Series1)
~20%
decline
1958 to 1996 average inflow is 574 GL
1997 to 2003 Average inflow is 397 GL (-30%)
800000
200
700000
150
600000
100
South-coastal1950
Australian
April-July500000
Pressure (hPa)
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
1023
1022
2
300000
R = 0.1497
200000
1020
1019
100000
1018
0
1017
19
58
19
61
19
64
19
67
19
70
19
73
19
76
19
79
19
82
19
85
19
88
19
91
19
94
19
97
20
00
20
03
Pressure (hPa)
1021
400000 Year
y = 0.0411x + 936.82
1016
1015
1014
1013
1012
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Year
A slow forcing give rise to a
rapidly changing resource
outcome.
The SE
Australian 10
Year Drought
An unprecedented and
protracted hydrological
drought affecting much
of southeast Australia
Also, warmest period
on record.
Temperature and Rainfall
800
3.0
700
2.0
600
1.0
500
0.0
400
-1.0
300
-2.0
200
-3.0
100
-4.0
0
1950
1955
1960
1965
1970
1975
1980
Year
1985
1990
1995
2000
-5.0
2005
Max Temp anomaly (C)
Rainfall (mm)
Murray Darling Basin - April-December
Increased temperatures have
increased moisture stress
The drought of 2002 was
one of Australia’s most
severe due to record high
temperatures, not record
low rainfall.
Vegetation health (condition) due to water availability and
temperatures, based on satellite data.
Drought regions with vegetation under stress are shown
in red. (Kogan, 1997) Obtained from NOAA, USA from
http://orbit35i.nesdis.noaa.gov/crad/sat/surf/vci/aus.html
Future projections
of climate change
The latest IPCC assessment of
all scientific literature on Climate
Change is due for release next
year
It concludes that recent warming
is highly likely (>90% chance)
due to human influences on
climate.
Modelling centres around the
world are running forward
projections of climate that is
forced with expected increases to
greenhouse gases.
• Global mean warming
1.4-5.8C by 2100
• Mean sea-level rise 988cm by 2100
A synthesis of climate
models produces a
range of likely rainfall
changes in Australia
under global warming
scenarios
Almost all the models agree
on reduced rainfall for
Southern Australia
Model predicted
temperature changes
in Australia under
global warming
scenarios
Continental wide warming will
result from greenhouse gas
increases.
Conclusions
• Australia is a relatively dry country with a high natural
variability in its rainfall regime
• Natural and human systems have high capacity to deal with
such variability but are undoubtedly impacted by droughts,
bushfires, storms etc
• Climate in Australia is changing – temp, rainfall, mean,
extremes
• Extreme events; droughts, record high temps, bushfires
impact more obviously on biosphere than changes in mean
Conclusions
cont…
• Changes in rainfall regimes already noted can be
interpreted in terms of changing dynamical
patterns
• The combined impact of temperature and rainfall
changes can be severe for the biosphere
• Projections indicate a drier southern Australia with
hints of a drier eastern Australia and a wetter
north-west Australia but higher temperatures are
clear everywhere
Extreme and Mean Rainfall
Variations Over Australia
Rainfall deficiencies consistent with variations in mean. Some
years “drought free” others “drought dominates Australia”
Summary of Current Climate
Change/Long-Term Variability
Knowledge
Variable
HQ set
Observed Changes Attribution
Temperature
Yes... but
Warming
everywhere
Yes
Rainfall
Yes... but
Increasingly strong
trends
Generally no
(except SWA)
Evaporation
Nearly
Little change
Drought
No
Uncertain... but
Extremes
For some
(TCs, storms, fire weather, variables
high inflows)
Uncertain/Mixed
Seasonal Signal
AUT
WIN
SPR
SUM