The role of climate variability and climate change in NSW water sharing arrangementsRichard Beecham (Water Modelling)
Shahadat Chowdhury (Water Modelling)
Mark Harris (Planning and Policy)
OVERVIEW OF TALK
Water resource plans in NSW Climate variability in developing the plans Climate variability versus climate change Future planning challenges
This presentation is relevant to large regulated rivers in NSW.
Unregulated rivers and aquifers have different challenges.
DEVELOPMENT OF WATER PLAN
Water Sharing Plans in NSW set the rules for sharing water between the environment and different consumptive users.
The plans are set for a ten year period. Plan is designed for climatic conditions that are likely to occur. Input: historical rainfall, evaporation, temperature and inflow
over 1895 to 2010 The impacts of various proposals are scrutinised using
numerical river system models.
TIME SERIES OF ANNUAL IRRIGATION DIVERSION
CURRENT PLAN’S RESPONSE TO CLIMATE STATE
PERIOD % of long term mean
Inflows Diversions
1893-2008 100 100
DRIEST DECADE 50 80
WETTEST DECADE 195 110
Simulated response of the Namoi Water Sharing Plan to climate variability
Ref: NamoWSP2010.sqq
CLIMATE VARIABILITY ISSUES
Do we understand climate variability well? Is 120 year data sequence long enough to reflect the extremes?
Statistical generation of longer time series may help simulate rare events.
Some limited palaeo studies indicated longer dry spells than the one found in the historical record.
Should the plan cater for extremes with say 500 year frequency?
Would that be a too risk averse plan?
FUTURE WATER PLAN CHALLENGES
More complex environmental or ecological targets. The need to consider climate change (key directive).
– National Water Initiative
– National Water Commission
– Commonwealth Water Act 2007
Significant uncertainty in quantifying the hydrological impact of climate change.
Demanding accreditation test – Eg. the Guide to the proposed (Murray Darling) Basin Plan. The
reduction of decadal water extraction at the same rate to any reduction of available water over that decade.
PLANNING IN STATIONARY CLIMATE
10 YR
VA
RIA
BIL
ITY
PLAN LIFE
Ann
ual R
ainf
all (
mm
)
Residual mass curve
NON STATIONARY CLIMATE STATE
10 YR
VA
RIA
BIL
ITY
PLAN LIFE
STATIONARY NON STATIONARY
YEARRA
INF
ALL
REFERENCE YEAR(2030 for Basin Plan)
MODELLING FUTURE CLIMATE
Options to estimate future climate time series Global Climate Model (GCM): 200 to 400 km grid Regional Climate Model (RCM): 10 km grid
– GCM to RCM: statistical or dynamical
Scaling of historical climate time series based on GCM– current practice
– computationally simple and provides long time series required for planning models
Scaling method
GCM/ RCM
ISSUES WITH GCM/RCM PROJECTION
Downscaling to be suitable for river system models, both in time and space scale. GCM to RCM– Computationally expensive.
Poor reproduction of historical rainfall including important low frequency events.
Large disagreements among different GCM’s rainfall projections.
Projections span from present to 2100. What should be the appropriate slice of time window to represent the climate variability during the life of the plan?
Selection of a short time window of GCM (10 year) means lower chance of experiencing long dry spells
SCALING METHOD
Poorly represent spatial differences of climate projections and hence do not represent altered spatial dependence expected due to climate change.
Do not alter historical long dry spell length, very important aspect of water planning! Hence underestimates extremes such as consecutive years of very low allocation.
d at e: 2 1 / 0 1 / 1 1 t i m e: 1 2 : 2 0 : 5 8 .6 0
W y an g al a D am S t o r ag e V o l u m e 2 0 3 0 C l i m at e C h an g e, M ed i an E m i ssi o n
0 1 /0 1 /1 8 9 6 t o 3 0 /0 6 /2 0 0 6
0
1 0 0
2 0 0
3 0 0
4 0 0
5 0 0
6 0 0
7 0 0
8 0 0
9 0 0
1 0 0 0
1 1 0 0
1 2 0 0
M
L*1
000
Y ear s
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
C u r r en t C l i m at eC l i m at e C h an g e
Note the dry spells are of similar length!
THE WAY FORWARD
“Prediction is difficult, especially about the future” Niels Bohr “… it is premature to make definitive statements about the
levels of uncertainty in climate change impact ….”, Bates et al. (2010), Waterlines Report 28, NWC
Risk based approach of water planning in NSW: – plan formulated using current knowledge (past climate variability)
– test the robustness of the plan on plausible scenarios beyond the historical record
– include contingency measures and triggers for unprecedented events
– review plan at the 10 year planning cycle (use any new information).
The End
Author contacts:
Richard Beecham, [email protected]
Shahadat Chowdhury, [email protected]
Mark Harris, [email protected]
SOME TYPICAL SIMULATION OUTCOMESIN THE PLANNING PHASE
What is the mean diversion over long term? : Important for comparison to 1993/94 MDB cap on diversion.
How often flows are available for environmental requirement (eg. end of system, wetlands) ? : Environmental outcome.
How often water allocation becomes low (say < 20%)? : Irrigation reliability.
What is the longest dry spell in terms of allocation? : Industry viability.
What is the lowest storage level? : Security of essential supply. … and many more
CLIMATE VARIABILITY VS CHANGE
Climate change can be defined as non stationary state of the climate.
Stationary: long term mean, spread (highs to lows), skew, persistence, seasonality, chance of rare events (extremes).
Our current modelling practice assumes stationarity, past long time series represents best estimation of future variability.
Climate Change : non stationary climate and hence past long time series may not be adequate to define future variability.
CURRENT PLAN’S RESPONSE TO CLIMATE STATE
AVERAGE MAJOR INFLOW
AVERAGE DIVERSION
AVERAGE END of SYSTEM FLOW
Full length
1893 to 2008
705 GL/a
(100%)
235 GL/a
(100%)
660 GL/a
(100%)
Driest decade
1936 to 1946
355 GL/a
(50%)
190 GL/a
(80%)
330 GL/a
(50%)
Wettest decade
1947 to 1957
1390 GL/a
(195%)
260 GL/a
(110%)
1590 GL/a
(240%)
Ref: NamoWSP2010.sqq
Simulated response of the Namoi Water Sharing Plan to climate variability
CURRENT PLAN’S RESPONSE TO CLIMATE STATE
AVERAGE MAJOR INFLOW
AVERAGE DIVERSION
AVERAGE END of SYSTEM FLOW
Full length
1898 to 2008
750 GL/a
(100%)
280 GL/a
(100%)
100 GL/a
(100%)
Driest decade
1901 to 1911
435 GL/a
(60%)
265 GL/a
(95%)
40 GL/a
(40%)
Wettest decade
1948 to 1958
1480 GL/a
(195%)
335 GL/a
(120%)
210 GL/a
(210%)
Simulated response of the Lachlan Water Sharing Plan to climate variability
Ref: LachW018.sqq
FUTURE PLAN’S RESPONSE TO CLIMATE STATE
AVAILABLE WATER
SURFACE WATER
EXTRACTION
MAJOR INFLOW *
CURRENT
IRRIGATION*
Full length 100% 100% 100% 100%
Driest decade A % A% or less ~ 50% ~ 90%
Wettest decade B % B % or less ~ 200% ~ 110-120%
Climate change
Full length
C % C % or less 90-95% 90-99%
The Guide to the Basin Plan proposed the accreditation tests shown in first two columns:
*case study: Lachlan & Namoi