Climate Variability and Trends Climate Variability and Trends in Australiain Australia

David Walland

Bureau of Meteorology

Carbon-Drought Workshop

5-8 June

Canberra

OutlineOutline

• An introduction to Australian climate (rainfall) variability

• The emergence of climate change amongst the variability

• Projections

A Long History of Rainfall A Long History of Rainfall VariabilityVariability

• Australia is unique amongst developed countries. Natural and human systems must be adapted to a boom bust climate

Variability of Annual rainfall

0

2

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20

Australia S. Africa Germany France NZ India UK Canada China USA Russia

Country

Coe

ffic

ient

(%)

(100 years of data for Australia and generally also for the other countries)

Australian Rainfall - Droughts Australian Rainfall - Droughts and Delugeand Deluge

Impact on BiosphereImpact 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 Significant drivers of Rainfall VariabilityVariability

• 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 NinoThe Walker Circulation - “normal” and El Nino

Emerging Emerging Climate TrendsClimate Trends

High-quality rainfall dataset: Annual trends

Annual Rainfall For Australia

300

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450

500

550

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650

700

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800

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000Year

Rai

nfa

ll (

mm

)

5 Year Mean

High-Quality Annual High-Quality Annual TemperatureTemperature

• 1910-2005 trends:• Max T: +0.06°C/decade• Min T: +0.12°C/decade

Impact of ExtremesImpact 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 High-quality Daily Temperature: Daily Temperature: Daily

ExtremesExtremes

Hot Days: Max T Hot Days: Max T ≥≥ 3535ooCC

Cold Days: Max T Cold Days: Max T ≤≤ 1515ooCC

Hot Nights: Min T ≥ Hot Nights: Min T ≥ 2020ooCC

Cold Nights: Min T Cold Nights: Min T ≤≤ 55ooCC

• Shifts consistent with changes in mean• Averaged over “valid” regions only• Updated from Collins et al. (2000)

Average number of Hot Days/Nights and Cold Days/Nights

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40

60

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100

120

140

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

No

. p

er

year

Hot days (Max T = 35°C)Cold Days (Max T = 15°C)Hot Nights (Min T = 20°C)Cold Nights (Min T = 5°C)Linear (Hot days (Max T = 35°C))Linear (Cold Days (Max T = 15°C))Linear (Hot Nights (Min T = 20°C))Linear (Cold Nights (Min T = 5°C))

Sea Surface Sea Surface Temperature TrendsTemperature Trends

Smith and Reynolds (2004)Smith and Reynolds (2004)

• Free from urban influence, show rapid warming about SE Australia => interesting insight into the synoptic changes

El-NinoEl-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.

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.

Changing weather systems Changing weather systems & rainfall& rainfall

Impacts on water resourcesImpacts on water resources

A slow forcing give rise to a rapidly changing resource

outcome.

South-coastal April-July Rainfall (mm)

y = -0.9275x + 2083.3

R2 = 0.0798

100

150

200

250

300

350

400

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Rai

nfa

ll (m

m)

Series1

Linear (Series1)Southern Australian early winterRainfall (mm)

~20% decline

South-coastal April-July Rainfall (mm)

y = -0.9275x + 2083.3

R2 = 0.0798

100

150

200

250

300

350

400

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Rai

nfa

ll (m

m)

Series1

Linear (Series1)Southern Australian early winterRainfall (mm)

South-coastal April-July Rainfall (mm)

y = -0.9275x + 2083.3

R2 = 0.0798

100

150

200

250

300

350

400

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Rai

nfa

ll (m

m)

Series1

Linear (Series1)Southern Australian early winterRainfall (mm)

~20% decline

South-coastal Australian April-July Pressure (hPa)

y = 0.0411x + 936.82

R2 = 0.1497

1012

1013

1014

1015

1016

1017

1018

1019

1020

1021

1022

1023

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Pre

ss

ure

(h

Pa

)

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

1000000

1958

1961

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1967

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1982

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1988

1991

1994

1997

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2003

1958 to 1996 average inflow is 574 GL 1997 to 2003 Average inflow is 397 GL (-30%)

Total capacity is 1.770 GL

The SE The SE Australian Australian 1010 Year Year DroughtDrought

An unprecedented and protracted hydrological drought affecting much of southeast Australia

Also, warmest period on record.

Murray Darling Basin - April-December

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1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Rain

fall

(m

m)

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

Max T

em

p a

no

maly

(C

)

Temperature and RainfallTemperature and 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

The drought of 2002 was one of Australia’s most severe due to record high temperatures, not record low rainfall.

Increased temperatures have Increased temperatures have increased moisture stressincreased moisture stress

• Global mean warming 1.4-5.8C by 2100

• Mean sea-level rise 9-88cm by 2100

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.

Future projections Future projections of climate changeof climate change

A synthesis of climate A synthesis of climate models produces a models produces a

range of likely rainfall range of likely rainfall changes in Australia changes in Australia

under global warming under global warming scenariosscenarios

Almost all the models agree on reduced rainfall for Southern Australia

Model predicted Model predicted temperature changes temperature changes

in Australia under in Australia under global warming global warming

scenariosscenarios

Continental wide warming will result from greenhouse gas increases.

ConclusionsConclusions

• 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

ConclusionsConclusionscont…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 Extreme and Mean Rainfall Variations Over AustraliaVariations Over Australia

Rainfall deficiencies consistent with variations in mean. Some years “drought free” others “drought dominates Australia”

Summary of Current Climate Summary of Current Climate Change/Long-Term Variability Change/Long-Term Variability KnowledgeKnowledge

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

(TCs, storms, fire weather, high inflows)

For some variables

Uncertain/Mixed

Seasonal SignalSeasonal Signal

AUT

SPR SUM

WIN