Presentation by Don McFarlane, CSIRO on the effect of climate change on hydrology in the South West of Western Australia

1. The effect of climate change
on South West WA hydrology
Don McFarlane
Research Manager

2. Structure of the talk
1. Recent and projected climate change in South West WA
i. Rainfall amount and intensity
ii. Temperature
2. Wheatbelt
i. Groundwater levels and dryland salinity
ii. Streamflows and flooding
3. Darling Range
i. Groundwater levels
ii. Surface water yields
4. Perth Basin
i. Groundwater levels
ii. Surface water – groundwater interactions
5. Conclusions
The effect of climate change on South West WA hydrology

3. Location of the areas discussed
Perth Basin
Darling Range streams
Wheatbelt
Blue + pink = South West
Sustainable Yield project area
The effect of climate change on South West WA hydrology

4. South west WA annual rainfall has fallen since 1970
Bureau of Meteorology 2010
>60 mm
>120 mm

5. South-west WA has had reduced rainfall since
1975
May – July
August – October
600
500
-18%
Total rainfall (mm)
400
300
200
100 -8%
0
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
Change may have started in about 1965 and stabilised by 1975
The effect of climate change on South West WA hydrology

6. SWWA winter extreme rainfall has decreased since 1965
Li et al. 2005
90
Rainfall (mm) (on log scale)
80
70
60
50
40
Year 1930-1965
Year 1966-2001
30
1 10 100 1000
Return period (years) (on log scale)
The effect of climate change on South West WA hydrology

7. Annual rainfalls have been even drier since 1997
CSIRO 2009
1997 to 2007 rainfall
compared with
1975 to 1996 rainfall
The effect of climate change on South West WA hydrology

8. 14 of 15 GCMs project it will get drier
CSIRO 2009
Change in annual rainfall
• Median future climate -7%
• Wet extreme future -1%
climate (90 percentile)
• Dry extreme future -14%
climate (10 percentile)
Mid warming
High warming Low warming
The effect of climate change on South West WA hydrology

9. Temperatures have risen which increases
potential evapotranspiration and reduces soil water
Bureau of Meteorology 2010
Up to 0.60C
Up to 0.80C
Up to 0.40C

10. Projected
changes in
temperature
by 2030
CSIRO and BoM
2007

11. Groundwater levels
and salinity
in the Wheatbelt
The effect of climate change on South West WA hydrology

12. Slow fall in saline
valley floor
Yilgarn Examples of
Craton falling
groundwater
levels
5m fall since
2000 where
WT is deeper
Speed (2008)
1m fall
since 2000
Perth
Basin

13. Speed (2008)
Rising or stable
trends prior to
2000
Declining trends
irrespective of
geology, WT
depth or land use

14. Before 2000 most groundwater levels were rising
in northern and central regions. Now most are falling
Based on data in George et al. 2008
80
Pre 2000 Rising
Pre 2000 Falling
70 Post 2000 Rising
Post 200 Falling
60
Percent of bores
50
40
30
20
10
0
Northern Central South West South Coast (W) South Coast (E)
Region
The effect of climate change on South West WA hydrology

15. Land Monitor - dryland salinity spread 1989 to 1996 and hazard
Yellow = 1989 Red = 1996 Blue = salt hazard

16. Shire salinity
McFarlane et al. 2004
Percentage of Change Salinity Hazard as a
Percentage of shire shire with between 1989 Hazard Percentage of
with salinity in 1996 salinity in 1989 salinity and (ha) Shire
Shire 957,581 ha 859,306 ha 1996 salinity 5,464,834 ha
Boddington 1.2% 0.6% 0.61% 12,767 6.7%
Broomehill 4.1% 3.3% 0.75% 21,395 18.2%
Dumbleyung 6.0% 5.3% 0.67% 54,169 21.3%
Gnowangerup 3.3% 2.5% 0.80% 89,850 21.1%
Jerramungup 2.4% 1.8% 0.56% 125,571 19.3%
Katanning 7.3% 6.5% 0.77% 39,306 25.9%
Kent 5.5% 4.7% 0.78% 138,454 24.6%
Kulin 4.7% 3.8% 0.90% 84,794 18.0%
Lake Grace 7.7% 7.0% 0.68% 273,648 26.4%
Moora 7.7% 6.2% 1.46% 81,158 21.6%
Narrogin 4.9% 4.4% 0.55% 45,613 28.2%
Nungarin 11.1% 7.7% 3.40% 50,012 43.0%
Tambellup 8.6% 7.7% 0.92% 49,286 34.3%
Wagin 6.6% 5.8% 0.85% 56,488 29.0%
West Arthur 2.9% 2.2% 0.69% 72,640 25.7%
Wongan-Ballidu 10.9% 10.2% 0.70% 94,822 28.1%
Woodanilling 5.5% 4.7% 0.83% 36,217 32.1%
TOTALS 2.9% 2.6% 0.30% 5,464,834 16.8%
17,000 ha per annum
The effect of climate change on South West WA hydrology

17. Comparison of salinity extent and hazard
Method Extrapolation NLWRA 1998 Land Monitor
from studies McFarlane et al.
Ferdowsian et al. 2004
1996
Salt-affected in 1996 to 1.8M 4.4M 0.96M
2000 period (ha)
Annual rate of increase 75,000 55,000 14,000
(ha) 2000 to 2020 2000 to 2020 1989 to 1996
Final hazard area (ha) 6.1M 8.8M <5.5M
The effect of climate change on South West WA hydrology

18. Streamflow
and flooding
in the Wheatbelt
The effect of climate change on South West WA hydrology

19. Wet years for Narrogin in 25-year segments
(Hatton and Ruprecht 2001)
6
Wet years (number)
6
Wet years defined as above 1-in-10 year
5 annual recurrence interval
4
4
3
2
2
1
0
0
1900-1925 1925-1950 1950-1975 1975-2000
1900-1925 1925-1950 1950-1975 1975-2000
The effect of climate change on South West WA hydrology

20. Annual floodflow for the Avon (Walyunga)
Hatton and Ruprecht 2001
1200
Annual Maximum
Mean
1000
90th Percentile
800
Floodflo w (m 3/sec)
600
400
200
0
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Year
NB: Modelled flows from 1910 to 1969 and gauged data after 1969
The effect of climate change on South West WA hydrology

21. Blackwood Basin
The effect of climate change on South West WA hydrology

22. Land Monitor mapped Salinity 1998
The effect of climate change on South West WA hydrology

23. Valley Hazard
The effect of climate change on South West WA hydrology

24. Predicted peak flows of the Blackwood at Darradup with
January 1982 rainfall (Cyclone Bruno)
Hatton and Ruprecht (2001)
6000
Calibration
Prediction: Sc enario 1 - Salt-affec ted land area doubles
5000 Prediction: Sc enario 2 - Salt-affec ted land area trebles
Prediction: Sc enario 3 - Salt-affec ted land area quadr uples
4000
Flow (m 3/s)
3000
2000
1000
0
21/01/82 24/01/82 27/01/82 30/01/82
The effect of climate change on South West WA hydrology

25. Major catchments of the Avon River Basin
Ali et al. (2009)
Total area
~116,600 km2
Northam
Walyunga

26. % reduction in annual flow if rainfall is 10 and 20% less
Based on data from Ali et al. (2009)
10% rainfall 20% rainfall
reduction reduction
compared with compared with
1976 to 2003 1976 to 2003
0
-10
3 to 4 times
% change in annual flow
-20 reduction 3+ times
reduction
-30
-40
-50
Walyunga Northam
-60
-70
-80
The effect of climate change on South West WA hydrology

27. % reduction in peak daily flows if rainfall is 10 and 20% less
Based on data from Ali et al. (2009)
10% rainfall 20% rainfall
reduction reduction
compared with compared with
1976 to 2003 1976 to 2003
0
1 2
-10
2+ times
reduction
% change in peak daily flows
2+ times
-20
reduction
-30
Walyunga Northam
-40
-50
-60
The effect of climate change on South West WA hydrology

28. Groundwater levels and
surface water yields
in the
Darling Range
The effect of climate change on South West WA hydrology

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

30. Declining groundwater levels in Darling Range catchments
CSIRO 2009
1988 1992 1996 2000 2004 2008 1988 1992 1996 2000 2004 2008
0 10
2 Gordon L4622-5A Bates E4506-3A
Depth to groundwater (m)
Depth to groundwater (m)
12
4
14
6
8 16
10
18
12
20
14
16 22
1988 1992 1996 2000 2004 2008 1988 1992 1996 2000 2004 2008
26 0
Cameron L4521-0928 Cobiac K3817-3A
2
Depth to groundwater (m)
Depth to groundwater (m)
27
4
28
6
29 8
10
30
12
31
14
32 16
The effect of climate change on South West WA hydrology

31. Groundwater trend
Petrone et al. 2010
1
Groundwater Depth (m)
2
3
4
1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
•Increasing annual amplitude
bc1
•Decreasing groundwater depths
The effect of climate change on South West WA hydrology

32. Dam Inflow and Runoff Statistics
1950-2008
Rainfall and Runoff
Change Point
1969/1975
1989-2008
Runoff Only
Change Point 1997/2001
Petrone KC, JD Hughes, TG Van Niel, RP Silberstein 2010
Geophysical Research Letters
The effect of climate change on South West WA hydrology

33. Groundwater Level and Runoff
Runoff (mm)
50 100 150 200 250 300 350
1.0
1992
Max Groundwater Depth (m)
1.2 1991
1993 1989
1996
BC3
1999
1.4 1994 1990
2000
1988 BC2 BB3
1995 BB
1997
1.6 BC1 2
2005 1998
2003
2004
2008 BB1
2009
2007
1.8 2001
2002
BA3
2.0 BA2
BA1
2006
2.2
Runoff (mm)
50 100 150 200 250 300 350 Runoff (mm)
0
1989 1992 50 100 150 200 250 300 350
Max Groundwater Depth (m)
1991 0.8
1988
Max Groundwater Depth (m)
1993 1992
1.0
1 19961990 1991
1999
1989
1997
2000 1994
1995 1.2 1993
1998 1994 1988 1990
1996
2009 1.4
2 2004
2003 1995
2005 2000
1999
2002
2007
2008 1.6 1997
2003
2001 2001 2007
2005 1998
2004
3 1.8
2006 2002
2009
2008
2.0
2006
2.2
The effect of climate change on South West WA hydrology

34. Equilibrium shift in Drying Climate?
• Reduction in saturated area
GW-SW Connection (groundwater discharge zone)
w
rflo and “saturation excess overland
Inte flow”
oam • Reduction in groundwater
da nd L y) baseflow
San e (Cla
lid Zon • Reduction in interflow
Pal
Ro ck
ent
Ba se m
w
Eq Loss of GW-SW Connection nte
rflo
uil I
ib ri u oam
nd L
m Sa nd a
Sh Cl a
y)
ift Zone (
Pa llid
Ro ck
ent
Ba se m
after Croton and Bari 2001
The effect of climate change on South West WA hydrology

35. Projected change in mean annual runoff relative to
the historical climate (1976 – 2007)
• Runoff declines by 25% under median future climate and 42% under dry climate
The effect of climate change on South West WA hydrology

36. Percent decline in runoff in all basins
Northern region Central region Southern region
d
st
oo
oa
kw
al
C
st
ac
oa
n
k
n
Bl
lly
to
ar
n
C
no
y
n
y
el
ne
to
Change in mean annual runoff (%)
ve
er
n
m
ra
re
an
lie
ss
an
gi
es
nt
w
en
on
ur
ar
ar
in
ol
Sw
Bu
Ke
Sh
Lo
Pr
W
M
H
D
D
G
C
0
-10
-20
-30 Recent climate
Median future climate
-40
• Decline under a continuation of the recent climate (1997 to 2007) is
greatest from Gingin to Collie
• Decline under a median future climate is more uniform indicating that
southern basins may ‘catch up’ in the drying trend
The effect of climate change on South West WA hydrology

37. Groundwater levels
in the
Perth Basin
The effect of climate change on South West WA hydrology

38. Topography
• Short streams that arise 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 change Australia West WA hydrology
The effect of climateWestern on South Sustainable Yields Project – Overview

39. Land cover
• Surface water catchments
are mainly forested
• About 60% of the Perth
Basin is cleared about
56% of this being under
dryland agriculture
• The uncleared areas Gnangara
Mound
include coastal areas
north of Perth, the
Gnangara Mound and the
Blackwood Plateau
Blackwood
Plateau
CSIRO South-West change Australia West WA hydrology
The effect of climateWestern on South Sustainable Yields Project – Overview

40. Land cover likely to affect recharge / discharge
Groundwater
assessment areas
• 56% dryland agriculture
• 38% native vegetation
• 6% plantations, urban,
irrigated, open water
The effect of climate change on South West WA hydrology

41. Maximum depth of the watertable
in the southern half of the Perth Basin in 2007
• Coloured areas are potential
GDEs if not cleared
• Coastal plain soils have very
shallow watertables except
Gnangara and Spearwood
Dunes
• Plateaux areas mainly 22%
14%
have deep watertables 10%
46%
The effect of climate change on South West WA hydrology

42. Change in groundwater levels between 2008 and
2030 under climate and development scenarios
The effect of climate change on South West WA hydrology

43. Surface water -
groundwater
interactions
The effect of climate change on South West WA hydrology

44. Gaining and losing sections in Gingin Brook
CSIRO 2009
GAINING
LOSING
The effect of climate change on South West WA hydrology

45. Amount and proportion of baseflow will change as both
streamflow and groundwater levels reduce
Current base flow is about two-thirds of streamflow
Under a dry future climate baseflow may reduce
80 Groundwater discharge
70
Surface water flow
60
50
GL/year
40
30
20
10
0
1972 1977 1982 1987 1992 1997 2002 2007
The effect of climate change on South West WA hydrology

46. Collie groundwater basin level changes between
2008 and 2030
Groundwater levels are less affected near rivers
The effect of climate change on South West WA hydrology

47. Conclusions 1
• The SW of WA experienced a climate shift in about 1975 with rainfall
amounts and intensities reducing. The accompanying rise in
temperatures may be contributing to drier soils
• Groundwater levels in the northern and central Wheatbelt are mainly
falling and the rate of salinisation has slowed.
• Flooding in the Wheatbelt was projected to increase because of
salinisation and increased rainfall intensities
• However runoff and flooding have decreased and are projected to
decrease further as catchments dry and if intensities remain low or
fall further
• There have been major reductions in streamflows in northern jarrah
forest streams – initially due to the reduced rainfall and more
recently due to lower groundwater levels resulting in changes in
runoff processes
• This trend is projected to continue to more southerly streams
The effect of climate change on South West WA hydrology

48. Conclusions 2
• Groundwater levels under the Perth Basin are falling under
perennial vegetation and in the north but rising under dryland
agriculture in most areas
• Levels are expected to fall further in future or rise more slowly
under dryland agriculture in the south and central parts
• Where streams cross the Perth and Collie Basins they currently
gain fresh groundwater
• These trends may reverse and brackish or saline streamflow
may contaminate nearby fresh aquifers
• Water dependent ecosystems have already been badly
impacted by climate change and this is likely to worsen
• Hydrological processes need to be understood if future
projections are to reflect these changes
The effect of climate change on South West WA hydrology

49. Possible areas for post graduate study
• Surface water – groundwater interactions under climate change
(hydrology, isotopes to separate flow components, modelling)
• Managing vegetation to influence recharge and runoff in a drier
climate – e.g. Gnangara Mound post-pine areas
• The influence of lower rainfall, higher temperatures, higher
potential evapotranspiration and more CO2 on plants and
hydrology (i.e. vegetation is also changing as a response to
climate change so hydrological impacts are complex)
• Methods of reclaiming saline Wheatbelt valleys where
groundwater levels have receded
• Ways of retaining important water dependent ecosystems in a
drying climate (e.g. use of stormwater and treated wastewater
to augment natural flows)
The effect of climate change on South West WA hydrology

50. Questions?
CSIRO South-West change Australia West WA hydrology
The effect of climateWestern on South Sustainable Yields Project – Water Yields and Demands