The effect of climate change on surface water - CSIRO Land and Water

<strong>The</strong> <strong>effect</strong> <strong>of</strong> <strong>climate</strong> <strong>change</strong> on surface water run<strong>of</strong>f
in south-west Western Australia
Richard Silberstein
Surface Water
Modelling Team

Acknowledgements
• DEWHA – funding and policy guidance
• Department <strong>of</strong> Water – data, models, researchers, report review
• Water Corporation – data, report review
• Department <strong>of</strong> Agriculture and Food WA – soils data
• Bureau <strong>of</strong> Meteorology – <strong>climate</strong> data, surface water modelling
• Queensland Department <strong>of</strong> Environment and Resource
Management – SILO data
• Contracts and consultancies
• Geographic Information Analysis – model data preparation
• External reviewers:
Ian Loh (Dept <strong>of</strong> Water), Peter Davies (University <strong>of</strong> Tasmania);
Andy Pitman (University <strong>of</strong> New South Wales); Tony Jakeman (ANU);
Don Armstrong (Lisdon Associates) and Murray Peel (University <strong>of</strong>
Melbourne)
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Surface water team
CSIRO
• Richard Silberstein, Santosh Aryal, Ge<strong>of</strong>f Hodgson, Tom Van
Niel, Irina Emelyanova, Jeanette Crute, Christina Gabrovsek,
Neil Viney, Ang Yang
Department <strong>of</strong> Water
• Mark Pearcey, Jacqui Durrant, Michael Braccia, Lidia Boniecka,
Kathryn Smith, Simone McCallum
Bureau <strong>of</strong> Meteorology
• Mohammed Bari
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Publications
Factsheet
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
Surface water main report Executive summary
Web: www.csiro.au/partnerships/SWSY.html
Hard copies can be obtained from: Katrina.Willis@environment.gov.au

Talk outline
• Introduction
• Climate scenarios
• Methods and models
• Results
• Key findings
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Sustainable Yields Projects – 2007 to 2009
Murray-Darling Basin
Northern Australia
South-West Western Australia
Tasmania
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Objectives
• Project future quantity, duration and seasonal distribution
<strong>of</strong> run<strong>of</strong>f (mm) and streamflow (ML) in south-west WA for
conditions in 2030
• under specified <strong>climate</strong> scenarios, and
• with future plantations and farm dams
• <strong>The</strong>se results were used in estimating divertible yields
and impacts on ecosystems
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Project context
This Project
Assessments
<strong>of</strong> current and
future water
yields and
demands
Environmental impacts <strong>of</strong>
alternate allocation regimes
Socio-economic impacts <strong>of</strong>
alternate allocation regimes
Stakeholder and community
consultation
• <strong>The</strong> project is regional and does not address local issues
• <strong>The</strong> project does not attempt to set new allocation limits
• <strong>The</strong> results are scenarios based on assumptions about the future
<strong>climate</strong>, land uses, abstraction levels and demands
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
Water
resource
planning,
management
and
investment

Location <strong>of</strong> the project area
• All fresh, marginal and
brackish surface water
catchments between
Gingin Brook and the
Hay River
• 38,800 km 2 <strong>of</strong> surface
water catchments
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Project area topography
• Short streams that rise in the
Darling Ranges are fresh
• Darling Fault separates Perth
Basin from Darling Plateau
• Coastal plains are flat and low
lying – Swan Coastal Plain;
Scott Costal Plain; South Coast
• Perth Basin Plateaux are higher
in elevation
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Climate – annual averages, 1975 to 2007
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
Potential
evaporation
(APET)
Rainfall - APET

South-west WA has had reduced rainfall since 1975
Total rainfall (mm)
600
500
400
300
200
100
0
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
-18%
-8%
May – July
August – October
<strong>The</strong> 1975 to 2007 period is the baseline for all subsequent comparisons

Annual rainfalls have been even drier since 1997
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
1997 to 2007 rainfall
compared with
1975 to 1996 rainfall

Annual rainfall and inflow into Perth dams
Run<strong>of</strong>f is affected by <strong>climate</strong> and other factors
Annual Rainfall at Jarrahdale (mm)
Annual Inflow to Perth Dams (GL)
2500
2000
1500
1000
500
0
1000
900
800
700
600
500
400
300
200
100
0
1911
1911
1914
1914
1917
Yearly rainfall at Jarrahdale
Yearly streamflow for major surface water sources - IWSS
1917
1920
1920
1923
1923
1926
1926
1929
1929
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
1932
1932
1935
1935
1938
1938
1941
1941
1944
1944
1947
1947
1950
1950
1953
1953
1956
1956
1959
1959
1962
1962
1965
1965
1968
1968
16%
reduction
Note: A year is taken as May to April (Data courtesy <strong>of</strong> the Water Corporation)
1971
1971
1974
1974
1977
1977
1980
1980
1983
1983
1986
1986
Annual Total
1911 to 1974 (1251mm)
1975 to 2009 (1047mm)
1997 to 2009 (1003mm)
1989
1989
1992
1992
1995
1995
1998
Annual Total
1998
2001
2001
2004
1911 to 1974 (338GL)
1975 to 2009 (151GL)
1997 to 2009 (107GL)
55%
reduction Historical
2004
2007
2007
Recent

Scenarios
• <strong>The</strong> ‘historical <strong>climate</strong>’ assumed that the <strong>climate</strong> <strong>of</strong> the last 33 years
(1975 to 2007) would continue. This was used as a base case for
comparison with other scenarios
• <strong>The</strong> ‘recent <strong>climate</strong>’ assumed that the <strong>climate</strong> <strong>of</strong> the last 11 years
(1997 to 2007) would continue
• <strong>The</strong> ‘future <strong>climate</strong>’ used 15 GCMs with 3 ‘greenhouse’ gas emission
levels which would result in 0.7, 1.0 and 1.3 o C warming by 2030
= 45 possible <strong>climate</strong>s. <strong>The</strong>y are reported as
• wet future <strong>climate</strong>
• median future <strong>climate</strong>, and
• dry future <strong>climate</strong>
• Current levels <strong>of</strong> land use and diversions were assumed to continue
for all scenarios above
• <strong>The</strong> ‘future <strong>climate</strong> and development’ scenario assumed a median
future <strong>climate</strong> and new plantations and farm dams (where important)
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

14 <strong>of</strong> 15 GCMs project it will get drier
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
Change in annual rainfall
• Median future <strong>climate</strong> -7%
• Wet (90 percentile)
future <strong>climate</strong> -1%
• Dry (10 percentile) -14%
future <strong>climate</strong>
High warming
Mid warming
Low warming

Geographic scope
• 13 surface water
basins covering
39,000 km 2
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Land use in the surface water basins
Land use in the surface
water modelling area is:
• 69% perennial native
vegetation
• 1% tree plantations
• 27% dryland agriculture
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Methods and Models
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Rainfall run<strong>of</strong>f modelling
• Run<strong>of</strong>f simulated using five simple conceptual models
• Sacramento
• IHACRES
• SIMHYD
• AWBM
• SMARG
• One catchment model
• LUCICAT (in about half the catchments)
• <strong>The</strong> calibrated model output was compared with observed
data and an average <strong>of</strong> run<strong>of</strong>f from Sacramento and
IHACRES was the best
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Catchment representation
Collie Basin
• 0.05 o x 0.05 o grid (~ 5 x 5 km)
• Each cell mapped into a catchment
• Flow accumulated for 204 defined streamflow reporting nodes
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

106 Calibration catchments
Criteria for use in calibration:
• Catchments larger than 10 km2 • At least 10 years <strong>of</strong> available
streamflow data between 1975
and 2007 (average record length
27 years)
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Calibration results – examples
Annual run<strong>of</strong>f (mm) .
Annual run<strong>of</strong>f (mm) .
500
400
300
200
100
0
400
300
200
100
0
Harvey River - Dingo Road Observed
Modelled
Scott River - Brennan's Ford Observed
Modelled
1975 1985 1995 2005
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
Modelled annual run<strong>of</strong>f (mm)
Modelled annual run<strong>of</strong>f (mm)
500
400
300
200
100
0
400
300
200
100
0
NSE = 0.82
NSE = 0.87
0 100 200 300 400
Observed annual run<strong>of</strong>f (mm)

Calibration results
Run<strong>of</strong>f (mm)
600
450
300
150
Annual run<strong>of</strong>f vs rainfall
Bancell Brook – Waterous
0
600 800 1000 1200 1400 1600
Rainfall (mm)
1975-1994
1995-2007
• In about half <strong>of</strong> catchments, run<strong>of</strong>f coefficients have reduced over the
recent past (1995 to 2007) – that is, the same amount <strong>of</strong> rainfall
produces less run<strong>of</strong>f
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Calibration results
Run<strong>of</strong>f (mm)
600
450
300
150
Annual run<strong>of</strong>f vs rainfall Model – observed run<strong>of</strong>f
Bancell Brook – Waterous
0
600 800 1000 1200 1400 1600
Rainfall (mm)
1975-1994
1995-2007
• In about half <strong>of</strong> catchments, run<strong>of</strong>f coefficients have reduced over the
recent past (1995 to 2007) – that is, the same amount <strong>of</strong> rainfall
produces less run<strong>of</strong>f
• Our rainfall-run<strong>of</strong>f models are over predicting run<strong>of</strong>f during the recent
period
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
Modelled – observed (mm)
100
50
0
-50
Bancell Brook – Waterous
-100
1970 1980 1990 2000 2010
Year

104 Calibration catchments
80% <strong>of</strong> catchments modelling efficiency >0.8
Average model efficiency = 0.84
Nash-Sutcliffe Efficiency
1
0.9
0.8
0.7
0.6
616189
616039
616011
616002
614036
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
614005
613008
612034
612019
612001
610014
610003
Catchments from north-w est to south-east
609002
607220
607004
606002
603012
603001

Rainfall, run<strong>of</strong>f and run<strong>of</strong>f coefficient under historical
<strong>climate</strong>
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

15 global <strong>climate</strong> models project less run<strong>of</strong>f
inmcm
ncar_pcm
iap
cccma_t63
ipsl
miroc
cnrm
cccma_t47
ncar_ccsm
mri
mpi
gfdl
csiro
giss_aom
miub
Global <strong>climate</strong> models Averaged across the surface water basins
-50 -40 -30 -20 -10 0
Change in run<strong>of</strong>f from historical (%)
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
Run<strong>of</strong>f <strong>change</strong> across all basins
Wet future <strong>climate</strong> -10%
Median future <strong>climate</strong> -25%
Dry future <strong>climate</strong> -42%
High warming
Mid warming
Low warming

Projected <strong>change</strong> in mean annual rainfall relative to
the historical <strong>climate</strong>
• Rainfall declines by 8% under median future <strong>climate</strong> and 14% under dry <strong>climate</strong>
• Proportion <strong>of</strong> area receiving over 900 mm is: 37% under historical <strong>climate</strong>, 34% under
recent and wet future, 22% under median future, and 16% under dry future <strong>climate</strong>
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Projected <strong>change</strong> in mean annual run<strong>of</strong>f relative to the
historical <strong>climate</strong>
• Run<strong>of</strong>f declines by 25% under median future <strong>climate</strong> and 42% under dry <strong>climate</strong>
• Proportion <strong>of</strong> area generating 110 mm run<strong>of</strong>f is: 37% under historical <strong>climate</strong>, 34% under
recent and wet future, 22% under median future, and 16% under dry future <strong>climate</strong>
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Projected <strong>change</strong>s in rainfall and run<strong>of</strong>f
Surface water
modelling area
Historical
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
Percent <strong>change</strong>
relative to historical <strong>climate</strong>
mm Recent Wet Median Dry
Mean annual rainfall 837 -2% -2% -8% -14%
Mean annual run<strong>of</strong>f 98 -7% -10% -25% -42%
Frequency <strong>of</strong> rainfall
exceeding 900 mm
generating more than
130 mm run<strong>of</strong>f
1 in 5
years
1 in 9
years
1 in 8
years
1 in 14
years

Percent decline in run<strong>of</strong>f in all basins
Northern region Central region Southern region
• Decline under recent <strong>climate</strong> is greatest from Gingin to Collie
• Decline under median future <strong>climate</strong> more uniform across the area
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
d

Decline in streamflow in all basins
Northern region Central region Southern region
• Decline under recent <strong>climate</strong> is greatest from Gingin to Collie
• Decline under median future <strong>climate</strong> is greatest in southern basins
CSIRO South-West Western Australia Sustainable Yields Project – Surface water
d

Key Findings
Relative to the historical <strong>climate</strong>, under the median future
<strong>climate</strong>:
• Climate models project rainfall declines by an average <strong>of</strong> 8%
• Our modelling projects run<strong>of</strong>f declines by 25%
• Mean annual run<strong>of</strong>f declines by 24 mm and streamflow
declines by 800 GL in addition to the decline since the
mid-1970s
• Declines in run<strong>of</strong>f are proportionally greater in the northern
surface water region but streamflow volume declines are
greater in the central and southern regions
• Climate impact on projected streamflows after 2007 is much
greater than that <strong>of</strong> projected increase <strong>of</strong> plantations and
farm dams
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Contributors
Project Director Tom Hatton
Sustainable Yields Coord. Mac Kirby
Project Leader Don McFarlane
Project Support Frances Parsons, <strong>The</strong>rese McGillion, Paul Jupp, Josie Grayson
Data Management Ge<strong>of</strong>f Hodgson, Jeannette Crute, Christina Gabrovsek, Mick Hartcher, Malcolm Hodgen
DOW – Aidan Belouardi
DAFWA – Damien Shepherd, Dennis van Gool, Noel Schoknecht
Climate Stephen Charles, Francis Chiew, Randall Donohue, Guobin Fu, Ling Tao Li, Steve Marvanek,
Tim McVicar, Ian Smith, Tom Van Niel
NSW Dept <strong>of</strong> Water and Energy – Jin Teng
Surface Water Richard Silberstein, Santosh Aryal, Neil Viney, Ang Yang
DOW – Mark Pearcey, Jacqui Durrant, Michael Braccia, Kathryn Smith, Lidia Boniecka, Simone McCallum
BOM – Mohammad Bari
Geographic Information Analysis – Ge<strong>of</strong>f Mauger
Groundwater Riasat Ali, Warrick Dawes, Sunil Varma, Irina Emelyanova, Jeff Turner, Glen Walker, John Byrne,
Phil Davies, Steve Gorelick, Mahtab Ali
DOW – Chris O’Boy, Binh Anson, Phillip Commander, Cahit Yesertener, Jayath de Silva, Jasmine Rutherford
Water Corporation – Mike Canci, Chengchao Xu
Cymod Systems – Neil Milligan
URS Australia – Wen Yu, Andrew Brooker, Amandine Bou, Andrew McTaggart
Water Yields and Demands Olga Barron, Natalie Smart, Michael Donn
DOW – Roy Stone, Phillip Kalaitzis, Rob Donohue, Fiona Lynn, Adrian Goodreid, Andrew Paton,
Susan Worley, Kylie La Spina
Resource Economics Unit – Jonathan Thomas
Jim Davies and Associates – Sasha Martens, Kate Smith
Reporting Viv Baker, Becky Schmidt, Susan Cuddy, Simon Gallant, Heinz Buettik<strong>of</strong>er, Elissa Churchward,
Chris Maguire, Linda Merrin
Communications Anne McKenzie, Helen Beringen, Mary Mulcahy
CSIRO South-West Western Australia Sustainable Yields Project – Surface water

Questions?
Web: www.csiro.au/partnerships/SWSY.html
CSIRO South-West Western Australia Sustainable Yields Project – Surface water