Bill Young at Water Wednesday

1. Water Research Centre
Water Wednesday
Sustaining the River Murray with less water

2. Declining Streamflow – the Future for the
Murray-Darling Basin?
Bill Young
Director, Basin Plan Modelling
Murray-Darling Basin Authority
15 July 2009, Water Research Centre, University of Adelaide

3. Overview
• The current drought in the historical context
• Climate change projections
– Rainfall and runoff
– Water availability
– Use under current water sharing arrangements
– Impacts on end of system flows

4. Natural flow to the sea

5. Growth in storage capacity & diversions
40,000
Capacity major storages
35,000
Average annual flow of all rivers (without-development)
30,000 Average natural flow to the sea
Total surface water diversions
25,000
Volume (GL)
20,000
15,000
10,000
5,000
0
1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

6. Flows over the barrages

7. Reduction in Barrage flows
• Natural flows at barrages
– 1895 – 2006 12,200 GL/yr
– 1987 – 2006, 86% of long-term average 10,550 GL/yr
– 2002 – 2006, 46% of long-term average 5,570 GL/yr
• With current development/sharing
– 56% reduction over 1895 – 2006 (111 years) 5,090 GL/yr
– 62% reduction over 1987 – 2006 (20 years) 4,000 GL/y
– 96% reduction over 2002 – 2006 (5 years) 220 GL/yr

8. Percent difference in rainfall and runoff

9. Change (mm) in rainfall and runoff

10. Southern MDB Rainfall

11. Southern MDB Runoff

12. Is this just drought or is it global warming?
• Decline in Autumn rainfall
– Probably linked to intensification of sub-tropical ridge
– Decrease in frequency of La Nina events
– Both consistent with global warming predictions
• Other changes observed in climate system which are
consistent with global warming predictions
– More extreme and earlier than expected
• However, similar changes are known to occur as a part
of decadal scale climate variability

13. Recent climate: reduced autumn rainfall
80
70
60
50
40
30 1895 – 2006
1997 – 2006
20
1936 – 1945
10
1895 – 1904
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

14. Recent climate: reduced autumn runoff
% Difference from long-term mean
16
Rainfall Runoff
1997-2006 -13 % -39 %
14 1937-1946 -14 % -22 %
1895-1904 -11 % -31 %
12
10
8
6
4 1895 – 2006
1997 – 2006
2 1936 – 1945
1895 – 1904
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

15. Best conclusion…
“It is likely that climate change is contributing
to the current drought both through
increased temperatures and a shift in rainfall
drivers towards a phase associated with
lower rainfall in the southern MDB”
Accurate quantification of this contribution remains
a difficult and ongoing research issue…

16. Percent changes in runoff by 2030

17. Percent changes in runoff by 2030

18. Climate change projections for MDB
High global warming
80 80
Northern MDB Southern MDB
40 40
0 0
Runoff change (%)
-40 -40
-80 -80
2070 1990 2010 2030 2050 2070 1990 2010 2030 2050 2070
Medium global warming
80 80
Northern MDB Southern MDB
40 40
0 0
-40 -40
-80 -80
2070 1990 2010 2030 2050 2070 1990 2010 2030 2050 2070

19. Median 2030 streamflow reductions

20. Dry extreme 2030 streamflow reductions

21. Streamflow reduction due to diversions

22. Impact of climate by region
• MDB: median impact is an 11% reduction in available water
– ranges from 2% to 21% reduction across regions
– ~2500 GL/year across MDB on average
• Consequence under current water sharing arrangements is a 4%
reduction in surface water diversions
– ranges from 1% increase to 11 percent decrease across regions
– ~450 GL/yr across MDB on average
5%
Change under median 2030 climate (%)
0%
-5%
-10%
-15%
Surface water availability
-20%
Surface water diversions
-25%
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23. Change in annual surface Change in annual surface
Change in annual surface
water diversions (%) water diversions (%)
water diversions (%)
-60%
-50%
-40%
-30%
-20%
-10%
0%
10%
-60%
-50%
-40%
-30%
-20%
-10%
0%
10%
-60%
-50%
-40%
-30%
-20%
-10%
0%
10%
Co Pa
nd
am W roo
ine a rre
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Bo M ne Average
rd oon
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1-year lowest
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Change in diversions in dry years
Ra era
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es
Change in annual surface
Change in annual surface Change in annual surface
water diversions (%)
water diversions (%) water diversions (%)
-100%
-80%
-60%
-40%
-20%
0%
Co
-100%
-80%
-60%
-40%
-20%
0%
-100%
-80%
-60%
-40%
-20%
0%
20%
nd Pa
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1

24. Impact sharing – median 2030 climate
Use Loss Outflow
0%
-5%
-10%
Change (%)
-15%
-20%
-25%
-30%

25. Flow over the barrages – no diversions

26. Flow over the barrages – current sharing

27. End of Basin flows
• Total flow at the Murray mouth reduced by 61 percent
• Flow ceases 40 percent of the time compared to 1 percent of the
time in the absence of consumptive use
• Severe drought inflows to Lower Lakes (<1500 GL/year)
– Never under without-development conditions
– 9 percent of years at current development with historical climate
– 13 percent of years under median 2030 climate
– 33 percent of years under dry extreme 2030 climate
1895 1915 1935 1955 1975 1995

28. Conclusions
• We are in a severe drought which can be partly
attributed to climate change
• The recent period very low flows over the barrages is a
result both of drought and surface water diversions
• Current water sharing arrangements would transfer a
disproportionate fraction of the impact of anticipated
climate change to the environment
• The new Basin Plan will set sustainable diversion
limits on all water resources considering the range of
possible future climate conditions

29. Acknowledgements
• CSIRO MDB Sustainable Yields Project
• National Water Commission
• Francis Chiew, CSIRO (SEACI Project)