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
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
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…
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%
a
e
oi
ee
g
e
on pe
am n
ca
n
s
go
o
s
ir
y
ns
gh
er
nn
ni
li n
ge
e
la
ra
am
er
ro
yd
dg
s
vo
re
ve
ok
m
ea
ch
oo
iv
lo
Pa
ar
ur
pa
an
w
im
N
ar
bi
-A
O
R
Br
Ba
Ba tler
La
M
M
-D
G
R
m
W
W
n-
er
on
e-
ru
as
fty
ur
C
rd
dd
in
rw
ur
-C
Lo
lb
Bo
m
Lo
M
ou
ie
da
nt
ar
G
ou
on
qu
M
C
ac
n
M
er
st
Ea
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
-B go
al
on
Bo M ne Average
rd oon
er
1-year lowest
Ri ie
M ve
ac G rs
qu wy
ar di
ie-
Ca Na r
Ba s tle mo
rw r e i
on ag
-D h
ar
l
M La i ng
ur
ru c hla
m
bi n
dg
M ee
G ur
ra
ou y
lbu Ov
rn en
-B s
Ca rok
Lo mp en
Ea dd a
st on spe
er
n -A
M v
tL W oc a
im
of
ty m
Change in diversions in dry years
Ra era
ng
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
am W roo
i ar
1
24. Impact sharing – median 2030 climate
Use Loss Outflow
0%
-5%
-10%
Change (%)
-15%
-20%
-25%
-30%
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)