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Climate change and water resources
Professor Nigel Arnell
Walker Institute for Climate System Research
University of Reading
ODI Climate Change and International
Development, March 2009
Impacts of climate change?
Overview
• What are the potential consequences of
climate change (in the absence of any
action)?
• What are the effects of mitigation?
• What are the implications of uncertainty for
adaptation?
• New developments
Consequences of climate change
IPCC Technical Report 2008
Summary of state of scientific
understanding in 2006-7
Assessment of reviewed literature
Key IPCC Technical Report conclusions
Changes in water quantity and
quality due to climate change
are expected to affect food
availability, stability, access and
utilizationClimate change affects the
function and operation of
existing water infrastructure as
well as water management
practices
Several gaps in knowledge
exist in terms of observations
and research needs
Not much on practical
experience with climate change
Not much from developing
countries
Future hydrological changes
A1b emissions scenario, multi-model ensemble mean, change by 2090-2099 relative to 1980-1999. White areas denote regions with little agreement
IPCC AR4
Hydrological consequences
• Change in timing of streamflow through the
year
• Change in the frequency of occurrence of
extreme high and low events
• Change in the contribution of glacier melt to
downstream runoff
• Potential for widespread deterioration in
water quality
From consequence to impact
Hydrological change
Water resources impact
Characteristics of
the “water
management
system”
Other drivers of
change
Vulnerability:
characteristics of
exposed system
Effects of mitigation?
“Do nothing”
“Mitigate”
Peak emissions in
2016; decline
thereafter
Committee on Climate Change
Hydrological consequences
Reference scenario change in runoff by 2080
Difference between reference scenario and policy scenario
Effect on water resources stresses
Increase in stress
0
200
400
600
800
1000
1200
1400
1600
reference 450ppmv reference 450ppmv reference 450ppmv
2020 2050 2080
Millio
ns o
f p
eo
ple
Numbers of people with increase in water resources stress due to
climate change
HadCM2 pattern, ADAM socio-economics
Uncertainty…
Hydrological effects of climate change depend on projections of future climate
Water resources impacts also depend on the exposed population
Implications for adaptation…
We cannot assume the past is a good guide
to the future
We cannot make forecasts of the future
Use scenarios to describe feasible
possible futures
How do we cope with multiple scenarios?
(i) By seeking to evaluate the relative
likelihood of different outcomes, and
taking a “risk-based” approach
(ii) By exploring sensitivity of decisions to
alternative scenarios; encourages robust
and flexible adaptation
New scientific developments…
• How might water resources and extreme
events vary from year to year?
• How might water resources vary over the
next few decades?
Variability and extremes
Current climate models do not simulate these well…
But new high-resolution models do…
The next couple of decades
Smith et al.
(2007) Science
Climate change will be superimposed onto patterns
of natural year-to-year variability
Met Office
Hadley
Centre
Conclusions…
• Climate change is impacting upon water
resources – but is not the only pressure
• Mitigation will reduce, but not eliminate, the
impacts of climate change
• Adaptation needs to consider explicitly
uncertainty
• We are understanding better changes in
variability and extremes
Thank you
Visit www.walker-institute.ac.uk
