Water availability, drought and climate change in the MDB: a hydrological perspective

Mac Kirby

MDB Water Policy Workshop, Brisbane

21 October 2010

Outline

• The Murray-Darling Basin Sustainable Yields project

• Results

• A closer look at drought

• Implications

The Murray Darling Basin (MDB)

• 1,000,000 km2

• 1/7 of Australia

• 80% of basin is agriculture

• 60% of Australia’s irrigation

• “Food Bowl” of Australia

• Population 2,000,000

• 6 jurisdictions

• Rainfall varies considerably from east to west

• 2400 mm in SE• < 200 mm in west

Rainfall and runoff characteristics

• Most runoff from small area

• Only rivers in south are reliable

Growth in storage capacity & diversions

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Vol

ume

(GL)

Capacity major storages

Average annual flow of all rivers (without-development)

Average natural flow to the sea

Total surface water diversions

Murray-Darling Basin Sustainable Yields Project

• Water Summit: Prime Minister and First Ministers, Nov 2006

• CSIRO to report progressively on sustainable yields of surface and groundwater systems within the MDB

• Estimate current and likely future (~2030) water availability in each catchment/aquifer and for the entire MDB considering:

• climate change and other risks

• surface-groundwater interactions

• Compare the estimated current and future water availability to that required to meet the current levels of extractive use

• Results reported for 18 regions and entire MDB through factsheets, summary brochures and technical reports.

Scenarios used in modellingHistoric climate (1895-2006) & current

development

Recent climate (1997-2006) & current development

Future climate & current development

• 2030 climate based on 4AR IPCC results

• 3 global warming levels (low, mid, high)

• 15 global climate models

• We choose a high extreme, median and low extreme for reporting

Future climate & future development

• Future development

• Commercial forestry plantations

• Farm dams

• Groundwater extractions

DJF JJA

SON MAM Autumn Summer

Winter Spring

Methods - overview

Surface and groundwater models used in the 18 MDB reporting regions

Paroo IQQM

Warrego IQQMNebine IQQM

Condamine MODFLOW

Middle Condamine IQQM

St George SGCS13NT

Lower Balonne IQQM

Upper Condamine IQQM

Mac. b and Bor. Riv IQQMBorder Rivers MODFLOW

Moonie IQQM

Gwydir IQQMLower Gwydir MODFLOW

Eastern Mt Lofty Ranges 6*WATERCRESS

DailyWeeklyMonthly

Barwon-Darling IQQM

Menindee IQQM

Peel IQQMUpper Namoi MODFLOW

Namoi IQQMLower Namoi MODFLOWMacq-Castlereagh 6*IQQMMacquarie MODFLOW

Wimmera REALMLachlan IQQMMid-Lachlan MODFLOWLower Lachlan MODFLOW

Ovens REALMGSM REALM

Avoca REALMSnowy SIM_V9

Murray BigModMurray MSM

Southern Riverine Plains MODFLOW

Upper Bidgee IQQMACTEW REALM

Mid Bidgee MODFLOW

Bidgee IQQMLower Bidgee MODFLOW

Th

e p

atte

rn o

f w

ater

ava

ilab

ility

Changes in seasonality3 Condamine-Balonne

at J ack Taylor Weir

0

100

200

300

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

9 Barwon-Darling

at Bourke

0

200

400

600

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

8 Macquarie

at Narromine

0

50

100

150

200

250

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

17 Murray

at Wentworth

0

500

1000

1500

2000

2500

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

11 Murrumbidgee

at Wagga

0

200

400

600

800

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

14 Goulburn-Broken

downstream of Lake Eildon

0

100

200

300

400

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

10 Lachlan

at Nanami

0

50

100

150

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

12 Murray

at Yarrawonga

0

500

1000

1500

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

1 Paroo

at Caiwarro

0

50

100

150

J F M A M J J A S O N D

Mon

thly

flow

(G

L)

Relative level of surface water use

• MDB: about half of available surface water is diverted for use• ~11,300 GL/year on average; from ~23,400 GL/year

0%

10%

20%

30%

40%

50%

60%

70%

Paro

o

Ovens

Easte

rn M

t Lof

ty Ran

ges

Barw

on-D

arlin

g

War

rego

Macqu

arie-

Castle

reag

h

Lach

lan

Lodd

on-A

voca

Bord

er R

ivers

Moonie

Campa

spe

Murra

y

Namoi

Gwydir

Goulbu

rn-Br

oken

Murru

mbidge

e

Conda

mine

-Balo

nne

Wim

mera

MDB

Rel

ativ

e le

vel o

f sur

face

wat

er u

se (

%) Historical climate Median 2030 climate

Low

Moderate

Moderately high

High

Very high

Extremely high

Relative level of use over 111 years

0

10,000

20,000

30,000

40,000

50,000

60,000

1895 1915 1935 1955 1975 1995

Ann

ual v

olum

e (G

L/y)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Relative level of use (%

)

Total flow

Surface water use

Relative level of use

Climate change - Percent changes in runoff by 2030

Med

ian

clim

ate

chan

ge

imp

act

Ext

rem

e cl

imat

e ch

ang

e im

pac

t

Impact of climate change on availability

• MDB: median impact is an 11 percent reduction in available water• ~2500 GL/year on average

0

500

1,000

1,500

2,000

Barw

on-D

arlin

g

Moonie

Easte

rn M

ount

Lofty

Ran

ges

Wim

mera

Campa

spe

Lodd

on-A

voca

War

rego

Paro

o

Gwydir

Namoi

Lach

lan

Bord

er R

ivers

Conda

mine

-Balo

nne

Macqu

arie-

Castle

reag

h

Ovens

Ave

rage

wat

er a

vaila

bilit

y (G

L/y)

Historical climate

Median 2030 climate

0

1,500

3,000

4,500

6,000

Goulbu

rn-Br

oken

Murru

mbidge

e

Murra

y

Change in volumes diverted for use

• MDB: 4 percent reduction in total diversions ~450 GL/year, with current sharing rules

0

50

100

150

200

250

300

350

400

450

Paro

o

Easte

rn M

t Lof

ty Ran

ges

Ovens

Moonie

War

rego

Wim

mera

Barw

on-D

arlin

g

Namoi

Lach

lan

Gwydir

Campa

spe

Lodd

on-A

voca

Macqu

arie-

Castle

reag

h

Bord

er R

ivers

Ave

rge

surf

ace

wat

er d

iver

sion

s (G

L/y)

historical climate Median 2030 climate

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Conda

mine

-Balo

nne

Goulbu

rn-Br

oken

Murru

mbidge

e

Murra

y

Additional future surface water uses

0

10

20

30

40

50

60

70

Paro

o

War

rego

Barw

on-D

arlin

g

Ovens

Wim

mera

Conda

mine

-Balo

nne

Moonie

Lodd

on-A

voca

Easte

rn M

ount

Lofty

Ran

ges

Campa

spe

Goulbu

rn-Br

oken

Gwydir

Lach

lan

Bord

er R

ivers

Namoi

Murra

y

Murru

mbidge

e

Macqu

arie-

Castle

reag

h

Add

ition

al s

urfa

ce w

ater

use

s (G

L/y)

Streamflow loss due to groundwater extraction

Additional commercial plantation forestry

Additional farm dams

A land of droughts….

• Droughts about every ten years

• Associated with El Nino

• Also long term cycles

0

100

200

300

400

500

600

700

800

900

1900 1920 1940 1960 1980 2000A

nnual ra

infa

ll, m

m

Major droughts

0

100

200

300

400

500

600

700

800

900

1900 1920 1940 1960 1980 2000

annual rain

moving average

Average 1900-1948

Average 1949-2000

median 1900-2007

Major droughts

Current drought in detail - runoff

• Not proven to be climate change

• Runoff dramatically down (especially 2006/7)

• Temperature increase

• Reduced autumn rain, reduced autumn and winter runoff

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

1900 1920 1940 1960 1980 2000

Annual te

mpera

ture

anom

aly

, degre

es

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

1900 1920 1940 1960 1980 2000

annual Tmean anomaly

moving average

Rainfall Runoff

SY project drought projections - eg runoff in Condamine

• Reflects general pattern of drought in the MDB

• Climate change dry extreme projection drier than historic

• Projection uses scaled historic, hence similar pattern

• Long dry runs with reference to historic median

0

500

1000

1500

2000

2500

3000

3500

1890 1910 1930 1950 1970 1990 2010

Annual ru

noff

, G

L

annual runoff

moving average

Average 1895-1948

Average 1949-2000

median 1895-2006

0

500

1000

1500

2000

2500

3000

3500

1890 1910 1930 1950 1970 1990 2010

Annu

al r

uno

ff,

GL

annual runoff

moving average

Average 1895-1948

Average 1949-2000

median 1895-2006

More, longer and more severe dry runs

Historic Climate change dry extreme

Runoff long dry runs

• Climate change projections show more, longer and more severe dry runs

• Impacts greater in south

• Dry extreme and median projections show great impacts

• Wet extreme similar to historical

Runoff

0

1

2

3

4

5

6

7

8

Nu

mb

er

of

lon

g d

ry r

un

s Historic Dry Mid Wet

Runoff

0

10

20

30

40

50

60

70

Nu

mb

er

of

years

a l

on

g d

ry r

un

Historic Dry Mid Wet

Runoff

0

20

40

60

80

100

Avera

ge p

rop

ort

ion

, % Historic Dry Mid Wet

Key messages

• Large proportion of surface water used for irrigation• Large year to year variation - short and long term• Large uncertainty in climate change projections - use as

planning scenarios• Despite the uncertainty all scenarios say the southern basin

will get drier• MDB median climate change impact is:

• 11 percent reduction in available water (2,500 GL/year)• 4 percent reductions in water use (450 GL/year)

• Impact of climate change expected to be considerably greater than ‘other risks’ BUT high uncertainty associated with climate impacts

Drought implications

• Recent drought in some ways different to past droughts - the past may not be a reliable guide to the future

• Need to consider scenarios outside the range of past experience, including climate change scenarios

• In recent drought there was insufficient water for either environment or irrigation. Current expectations could not be met. Extremely challenging, may be more so in future

• No easy fixes (more large dams irrelevant, for example)

• Improving irrigation (hydrological) efficiency may help, but

• Amounts to be saved may be modest

• Need to account for return flows

• Not lowest cost

www.csiro.au/partnerships/SYP.html

Murray-Darling Basin Sustainable Yields Project

funded byNational Water Commission