Transcript Is climate change affecting our water resources?

Is climate change affecting our
water resources?
Professor Nigel Arnell
Walker Institute for Climate System Research
Royal Geographical Society / Geographical Association
Southampton, November 15 2007
The summer of 2007
2006
2007
The summer of 2007: lessons
• There is a potential for repeat events
• The cost of weather events may be huge
• Unanticipated consequences
Walham Power Station
• Impacts resulted from a variety of
local circumstances
Diversity of local circumstances
Flash floods / overland flow / major rivers /
poor drainage of flat land
Thames
Pang
Sul
Trends in global hydrological regimes
Increase
Decrease
Milly et al. (2005)
1971-1998 compared with 1901-1970
The River Itchen
Itchen Brook: high flows > Q10
Number of high-flow days:
1960-2005
160
120
100
80
60
Itchen Brook: low flows < Q95
40
140
20
120
Number per year
2004
2000
1996
1992
1988
1984
1980
1976
1972
1968
1964
0
1960
100
80
60
40
20
2004
2000
1996
1992
1988
1984
1980
1976
1972
1968
0
1964
Number of low-flow days:
1960-2005
1960
Number per year
140
Future climate
• Change in climate
depends on:
- future emissions
- sensitivity of climate
to change
Future climate
IPCC AR4 WG1: Change in rainfall
white areas: lack of agreement between models
Climate change and water resources
Scholze et al. (2006)
Blue
tendency to increase
Red
tendency to decrease
Water scarcity
2055
Change in global water resources
Millions of people with increase in water stress
HadCM3 scenarios:
increase in stress
Millions of people
3500
3000
0.8-1.0oC
1.5-2.3oC
2.1-4.0oC
2500
2000
1500
1000
500
0
2025
2055
A1/B1
A2
2085
B1
B2
Impacts
depend on
change in
climate and
the state of
the world
Consequences
• Reduced access to safe water
Now: 1 billion people lack access to safe drinking water
2.4 billion people lack adequate sanitation
Access is not just a problem of availability
- property rights / power relations
Consequences
• Increased conflict over resources
• Increased exposure to floods
• Increased need for investment in water
management
What could happen in the UK?
Rainfall: 2050s
% difference from
1961-1990
Annual
winter
Runoff
UKCIP02 scenarios
summer
The catchment scale
Lambourn
50
50
30
10
-10
J F M A M J
J A S O N D
-30
% change from 1961-1990
% change from 1961-1990
Harper's Brook
Chalk
30
10
-10
J F M A M J
J A
S O N D
-30
-50
-50
Low
Low
M edium-low
M edium-high
M edium-low
M edium-high
High
Greta
High
Eastern England
2020s
% change from 1961-1990
50
Upland
30
10
-10
J
F M A M J
J A S O N D
-30
-50
Low
M edium-low
M edium-high
High
Scenario uncertainty
Harper's Brook
50
30
10
-10
J F M A M J
J A S O N D
-30
% change from 1961-1990
% change from 1961-1990
Harper's Brook
50
30
10
-10
J F M A M J
J A S O N D
-30
-50
-50
ECHAM 4
Low
M edium-low
M edium-high
High
GFDL
CSIRO
CGCM 2
CCSR
Harper's Brook
UKCIP02 scenarios
% change from 1961-1990
60
40
20
0
-20
-40
-60
Natural variability
J
F
M A
M
J
J
A
S
O
N
D
Annual runoff as % of 61-90 mean
-10
-20
-30
-40
2004
1999
1994
1989
1984
1979
1974
1969
1964
1959
Year-to-year variability
Itchen at Allbrook
60
50
40
30
20
10
0
Consequences for water resources
•
•
•
•
•
•
Floods
Water supply
Waste water treatment
Water quality
Instream ecosystems
Channel stability
Change in flood frequency
+15%
5 x as frequent
Reynard et al. (2003)
Implications for supply reliability
Severn-Trent
6.5% reduction by 2025
Thames / London
11-13% reduction by 2025
Climate change and other pressures
Resources are under pressure
without climate change
South East Water Southern Region
Water resource challenges
Assessments of current availability
Summer surface water
Groundwater
Environment
Agency
Climate change and water planning
OFWAT
-Periodic review of price limits
-Define investment requirements
Government “guidance” 2002
-consider climate change
-follow “twin-track” approach
Supply-side and demand-side
Environment Agency planning guidelines
-Specify a method to incorporate climate
change into yield and demand estimates
-Specify rules for making decisions
Context for planning guidelines
• Several hundred supply sources, with
limited information
- develop a generalised methodology
• Uncertainty over climate scenarios
- evaluate several scenarios
Methodological framework: PR04
Define climate scenarios and time horizon
- UKCIP02 scenario set 4 scenarios
- “industry standard”
Apply in 60 catchments with a range of hydrological
conditions
- use calibrated simple catchment model
Anglian region
20
Generalise to geographic regions
- regional average “flow factors”
% change in runoff
10
0
J
F
M
A
M
J
J
low
medlow
A
-10
-20
-30
-40
high
S
O
N
D
Methods for the next review
What will happen to resources over the next 20 years?
Deployable output
12
Scenarios derived from
several GCM runs
DO (MlD)
10
8
6
Interpolate backwards
from the 2020s
4
2
0
2005
2010
2015
Mid
2020
Low
2025
High
2030
2035
Science question: the next 20 years?
Natural variability will be very important
Initialisation of weather simulation models therefore
becomes very important
Role for
remote
sensing
Smith et al.
(2007) Science
Adaptation actions
Alter physical hazard
IMPACT
Alter exposure to the
hazard
Reduce vulnerability to
the hazard
Barriers to adaptation
Physical
- can we physically adapt?
Financial
- can we afford it?
Feasibility
- is it socially or politically acceptable?
Capacity
- do we have the institutional
capacity / methodologies to adapt?
What about mitigation?
Slow the rate of climate change
No climate policy
commitment
Van Vuuren (2007)
With policy targets
Effect of climate policy
“2oC target”
~ 0.8oC above 1961-1990 mean by 2020
~ 1.2oC above 1961-1990 mean by 2050
Summary
• Climate change is affecting hydrological
regimes, and will affect water resources
• The effects will be geographically variable
• The effects will depend on the state of
society - vulnerability
• We need to adapt AND to mitigate
What are the science opportunities?
Using high
resolution climate
models
Estimating
likelihoods
Decadal
forecasting
Thank you
www.walker-institute.ac.uk