Climate Change and Variability:Climate Change and Variability:

Observed trends for Australia, Observed trends for Australia,

NSW and the NSW and the NamoiNamoi

Perry Wiles

NSW Climate Services Centre

Climate Change and Agriculture Climate Change and Agriculture

21 & 22 March 200721 & 22 March 2007

Outline

� Climate variability in Australia and NSW

� Observed temperature trends

� Observed rainfall trends

“…of droughts and flooding rains”

Australian climate variability

Driest inhabited continent

High annual rainfall variability

Variability of Annual rainfall

0

2

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16

18

20

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

Country

Co

eff

icie

nt

(%)

Seasonal rainfall zones

Global atmospheric circulation

Source: The Greenhouse Effect and Climate Change, Bureau of Meteorology

Some sources of rainfall variability

Inter-decadalInter-decadal Pacific Oscillation

Inter-annualIndian Ocean Dipole

Inter-annualEl Niño (Southern Oscillation)

SeasonalSeasonal shifts in circulations

Month/sMadden-Julian Oscillation

WeeksSouthern Annular Mode

Day/weekWeather patterns

Approximate Time scaleKnown major causes

Observed climate change trends

� Detection

o Finding a trend “signal” in the variability “noise”

� Attribution

o What is causing any trend?

Observed Temperature Trends

Australian Temperature Trends

1910-2006 trends - Max T: 0.06°C/decade, Min T 0.12°C/decade

Australian Maximum Temperature Trends

Seasonal Maximum Temperature Trends

Winter

Spring

Autumn

Summer

MDB Maximum Temperature Timeseries

�1961-90 average 24.45°C

Local area maximum temperature trend

Annual Mean Maximum Temperature 1941 - 2006

(Rainfall Districts 53, 54, & 55)

22.5

23

23.5

24

24.5

25

25.5

26

26.5

1940 1950 1960 1970 1980 1990 2000

Year

Tem

pera

ture

(d

eg

C)

Australian Minimum Temperature Trends

Seasonal Minimum Temperature Trends

Summer

Winter

Spring

Autumn

MDB Minimum Temperature Timeseries

�1961-90 Average 24.45°C�1961-90 average 10.88°C

Local area minimum temperature trend

Annual Mean Minimum Temperature 1941 - 2006

(Rainfall Districts 53, 54 & 55)

8

8.5

9

9.5

10

10.5

11

11.5

12

1940 1950 1960 1970 1980 1990 2000

Year

Te

mp

era

ture

(d

eg

C)

Australian Temperature Extremes

Australian Temperature Extremes

Trends in growing season length

Observed Rainfall Trends

Australian rainfall trends since 1950

Australian rainfall trends since 1900

NSW annual rainfall time-series

New South Wales Annual Rainfall

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100

200

300

400

500

600

700

800

900

1000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

Rain

fall (

mm

)

Dry Period: 1900 - 1946

Average Rainfall: 477.7mm

*Dry conditions commenced 1890

Standard Deviation: 90.4

Wet Period: 1947 - 2000

Average Rainfall: 573.9mm

20.1% increase

Standard Deviation: 127.0

New

Dry

2001/06

439.5mm

23.4%

decline

NSW seasonal rainfall trends

75

95

115

135

155

175

195

215

2351900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Rain

fall (

mm

)

10 per.

Mov. Avg.

(Winter)

10 per.

Mov. Avg.

(Spring)

10 per.

Mov. Avg.

(Summer)

10 per.

Mov. Avg.

(Autumn)

Pre-1900 rainfall decline

Pre - 1900 rainfall decline

11 year moving average of annual rainfall

0

500

1000

1500

2000

2500

1857

1863

1869

1875

1881

1887

1893

1899

1905

1911

1917

1923

1929

1935

1941

1947

1953

1959

1965

1971

1977

1983

1989

1995

Rain

fall (

mm

)

Armidale

Grafton

Boggabri

Sydney

Goulburn

Shift in rainfall pattern in 1940’s

� Recognised for many years

� Not fully understood

� Project currently underway in NSW Climate Services Centre to seek to better understand what changed meteorologically and therefore get clues as to why

Change in annual average rainfall between the two periods 1900-1946 & 1947-2000 (%)

Clinton Rakich, NSW Climate Services Centre, Bureau of Meteorology

Change in annual average rainfall between the two periods 1900-1946 and 1947-2000

Change in annual average rainfall betweenthe two periods 1900-1946 and 1947-2000

Local Rainfall Trends

Annual Rainfall Timeseries for District 55

0

200

400

600

800

1000

1200

1400

18

90

19

00

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60

19

70

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80

19

90

20

00

Year

An

nu

al R

ain

fall

Local Area Seasonal Rainfall Trends

Seasonal Rainfall Timeseries for District 55

0

50

100

150

200

250

300

350

4001890/1

891

1900/1

901

1910/1

911

1920/1

921

1930/1

931

1940/1

941

1950/1

951

1960/1

961

1970/1

971

1980/1

981

1990/1

991

2000/2

001

Year

Ra

infa

ll (

mm

)

11 per. Mov.

Avg.

(Summer)

11 per. Mov.

Avg.

(Autumn)

11 per. Mov.

Avg. (Spring)

11 per. Mov.

Avg. (Winter)

Trends in extreme events

Average NSW Stations (25)

Number of heavy rainfall days

0

5

10

15

20

25

30

35

40

1870

1876

1882

1888

1894

1900

1906

1912

1918

1924

1930

1936

1942

1948

1954

1960

1966

1972

1978

1984

1990

1996

2002

Year

Nu

mb

er

of

da

ys

/ y

ea

rNumber of days with more than 10 mm's of rainfall / year20 mm's of rainfall / year30 mm's of rainfall / year11 per. Mov. Avg. (20 mm's of rainfall / year)

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

)

••Southern Australia has been experiencing increasing Southern Australia has been experiencing increasing summer/autumn pressures since 1950, delaying the summer/autumn pressures since 1950, delaying the winter rainfall season. winter rainfall season.

Observed changes in pressure/weather systems

Observed changes in pressure/weather systems

�� This is believed to be the driver for both the SW WA and This is believed to be the driver for both the SW WA and

SE (Vic and SE (Vic and SthSth NSW) autumn/winter rainfall declines NSW) autumn/winter rainfall declines

(although research is ongoing to understand the (although research is ongoing to understand the

underlying mechanisms)underlying mechanisms)

�� Latest modeling studies suggest that this is being driven Latest modeling studies suggest that this is being driven

by a combination of by a combination of

•• ozone depletionozone depletion

•• greenhouse induced climate change greenhouse induced climate change

•• natural variabilitynatural variability

(B. (B. TimballTimball, J. M. , J. M. ArblasterArblaster, S. Power, 2005), S. Power, 2005)

The recent dry period : 2001-2006

The recent dry period : 2001-2006

Thank you!

Recipe for rain

� Moisture source

� Moisture transport

� Lifting mechanism

o e.g. fronts, troughs, surface lows, convection, mountains

� Atmospheric instability

o e.g. mid level troughs, cut off lows, cold pools

� Condensation nuclei

Rain is a complex phenomenon requiring several

“ingredients” (most of which are interrelated) and each of

which could, in principle, be impacted by global warming

Some sources of rainfall variability

Inter-decadalInter-decadal Pacific Oscillation

Inter-annualIndian Ocean Dipole

Inter-annualEl Niño (Southern Oscillation)

SeasonalSeasonal shifts in circulations

Month/sMadden-Julian Oscillation

WeeksSouthern Annular Mode

Day/weekWeather patterns

Approximate Time scaleKnown major causes

Each of these sources of variability may also be impacted by global warming

Rainfall projections under climate change

� Why rain is difficult

� Latest IPCC 4AR projections

� Plans for new Australian regional projections

Inter-decadal Pacific Oscillation

See recent BMRC Research Report: Power et al. (2005)

Indian Ocean Dipole

Images courtesy of A.Suryachandra Rao of the Institute for Global Change Research, Yokohama City, Japan

New Australian & Regional Projections

� New joint CSIRO/BoM regional projections due to

be released at Greenhouse 2007, 2-5 October 2007

o based on IPCC 4AR models and scenarios

o will include probabilistic projections for rainfall and

temperature

� Statistically downscaled localised regional

projections are also being prepared by the Bureau

of Meteorology Research Centre as part of the IOCI

and SEACI projects (including the MDB)

Current CSIRO Australian Rainfall

Projections

Emerging Consensus on Projected Global Rainfall Changes

Rainfall change for 2090-2099 relative to 1980-1999.