Future flooding in the Eden:
Frameworks and models
Geoff Darch
Atkins (and Climatic Research Unit and
Tyndall Centre, University of East Anglia)
9 May 2011
Acknowledgements
Presentation summarises part of Geoff Darch’s part-time
PhD research (2003-2010), sponsored by Atkins and
supervised by Profs Phil Jones, Kerry Turner and
Richard Hey, as well as some new material.
Thanks to David Lister (CRU), Ben Lukey, Peter Spencer
and Nigel Worthington (Environment Agency) and Tom
Rouse, Paul Morgalla, Kevin Sene, Tracey Ashworth,
Yiping Chen, Chris Scott and Dominic Bradley (Atkins).
Data from UKCIP, UKMO, PRUDENCE, ENSEMBLES,
Newcastle University / Environment Agency (Profs Chris
Kilsby / Rob Wilby).
The challenge
The challenge for the future management of the
floodplain will be to balance changing resources
and risks. The floodplain, under demand for
myriad purposes, is likely to be a resource of
greater value, while climate and socio-economic
changes may increase risk.
Eamont Bridge
The challenge for scientists
The challenge for scientists is summarised by Everard
(1998: 481, emphases added):
[While] much of the basic science is already in existence
… the new challenge for scientists is not only to fill gaps
in our knowledge of these underpinning principles, but to
integrate them across their respective disciplines.
Ultimately, the regulatory community and Government
will require from the scientific community comprehensive
models of the processes upon which floodplains and
their ecosystems depend, in addition to the beneficial
processes that floodplains perform, from which
scenarios may be tested and evaluated in order to
develop sound sustainable policies.
Research gaps
●
The stability of river channels under (future) climate
change and implications for floodplains
●
The potential changes in land use in the catchment and
the effects on flooding at the catchment scale
●
The potential changes in land use on floodplains (beyond
development plans)
●
The potential impacts of climate change on future
flooding
●
The analysis of interactions between scenarios of climate
and land-use change (in the floodplain and wider
catchment) at the catchment scale
Contents
●
A framework for floodplain futures
●
Fulfilling the framework
●
A closer look at climate change
●
Alternative frameworks and models
Eden between Outhgill
and Kirkby Stephen,
looking upstream
A framework
for floodplain
futures
Scoping assessment for Eden
●
DP-S-I-R scoping framework (Turner, 2005)
●
Foresight Future Flooding study (Evans et al., 2004a,b)
generic drivers and response groups
●
Drivers:
– Climate change;
– Buildings and contents;
– Urban impacts;
– Infrastructure impacts;
– Social impacts.
●
Responses:
– Forecasting and warning
– Land-use planning;
– Insurance;
– River defences
Carlisle, south of Eden Bridge
Fulfilling the
framework
Socio-economics:
●
Limited techniques
for socio-economic
downscaling
(method
developed)
●
Few fully
distributed models
●
Some
understanding of
changes on
floodplains
(pathway and
receptor)
Fulfilling the
framework
Adaptation:
●
Non-structural
measures hard to
evaluate due to
lack of evidence,
modelling and
upscaling problem
A closer look at climate change
●
Numerous academic studies assessed climate change
impact on runoff; some in the Eden
●
Increasingly sophisticated use of climate model output
●
Not generally intended or applicable for decision-making
●
Treatment of climate change in decision-making models is
rudimentary and uses national allowance (generally 20%)
●
The allowance may not be sufficient and a national
allowance may not be appropriate (Reynard et al., 2009)
●
Research attempted to combine approaches and use
climate model output directly in design models: continuous
model (Bedford Ouse); discrete event model (Eden)
Eden
catchment
Area = 2,400 km2
AAR (1961-1990) =
1309 mm
94% agricultural
Several urban areas
(244,000 people)
Long history of
flooding
Eden flood model
●
Environment Agency hydrological-hydraulic model
●
FEH rainfall-runoff model (26 sub-catchments)
– three-component unit hydrograph and losses model
●
ISIS hydraulic model
– computes unsteady flows using a finite difference scheme
●
Flood forecasting (rather than design) version used
– simpler hydraulics
●
Three calibration events (February 1990, February 1995
and January 1999) are used (rather than design event)
– greater confidence in model performance
– design events of high return period cannot be perturbed for
climate change with confidence
Method
●
There is no simple or
conceptually satisfying
way to perturb a
hydrograph, or a discrete
event rainfall–runoff
model
...but it is possible (and
consistent with baseline
method), possibly better
than just adding 20%, and
this is research!
Gauge board, Appleby Pumping Station.
Potential method for a climate change perturbation of FSR/FEH rainfall–
runoff model inputs and parameters at gauged sites
*Based on the Eden results (see in particular page 259 of PhD thesis), future peak flows are most sensitive
to changes in storm depth (P) compared with average rainfall and event antecedent precipitation.
Chosen method
●
Proportional monthly change factor for storm rainfall depth
and antecedent rainfall
●
Proportional annual change factor for standard average
annual rainfall
Rainfall and flooding
Monthly areal precipitation series and the years of notable floods
for the Eden catchment above Warwick Bridge (1951–2002)
Original data from Prof Phil Jones (see Jones et al., 2006)
Monthly precipitation 2080s change factors for the Eden catchment
under different GCM–RCM combinations for the SRES A1B emissions
scenario
Note that the UKCIP02 2080s Medium-High scenario relates to the SRES A2 emissions scenario
Results: catchment hydrology
●
Peak runoff increases for all three events, for all 26
catchments, under all six scenarios, except in three
cases (out of 468)
●
Size depends on scenario and event
Change in peak
flow for the
Irthing
catchment for
the January
1999 event as
perturbed for the
2080s under
different
scenarios
Results: catchment hydrology
Number of catchments where baseline event peak flows are exceeded
by more than 20%
Results: catchment hydrology
Change in peak flow compared to change in monthly precipitation for
the Eden catchments for the February 1995 event as perturbed for
the 2080s under the SMHI-A1B-80 scenario
Proportional:
•Larger
•Wetter (SAAR and event)
•Higher SPR
Less than proportional:
•Smaller
•Drier (SAAR and event)
•Lower SPR
Receptors
Results: receptors
Change in peak flow at selected receptors for the 2080s compared
to the three historical events under different scenarios
Results: receptors
Change in water level at selected receptors for the 2080s
compared to the three historical events under different scenarios
Discussion of modelling approach
●
Benefits (fewer when compared to continuous simulation):
– Geographical interpretation of climate change
– Representation of some of the uncertainties
– Reasonably quick to implement
– Amenable to selection of events from stochastic series
●
Limitations:
– Minimal representation of antecedent conditions; does not
represent influence on PET
– Suitability of RCM outputs, even with bias correction
– Proportional change factor does not allow for change in variance
– Only some of climate uncertainties examined (‘ensemble of
opportunity’); not others, or hydrological uncertainties
Alternative frameworks
Scenario-led
Sensitivity-led
Scenarios
Impact models
Impact models
Sensitivity / impact
domain
Options
Options
Preferred
options
Preferred
options
Scenarios
Alternative frameworks
A simple comparison of scenario- and sensitivity- led approaches
Other alternative frameworks!
Policy-led
Resilience
Options
Scenarios
Sensitivity / impact
domain
Impact
models
Preferred
options
Preferred options
are those which
deliver resilience to
pressures;
resilience can be
precautionary (e.g.
design to
maximum likely
pressure) or nonspecific (e.g.
maximising
adaptive capacity
to any future)
Conclusions
●
Managing floodplains is complex
●
Challenge for scientists is to set out the risks
●
Scenario-based approach is one way to explore the future
●
Discrete-event hydrological model one tool
– Suggests climate change will increase flooding in the Eden
– Suggests that the 20% allowance may not be appropriate
– But method limited
●
Alternative frameworks may be more robust
●
In any case, need:
– appropriate catchment models (which models for which
purposes?)
– appropriate decision-making (decision-aiding) techniques
(optimisation, real-options, etc)
Eamont and Ullswater from Pooley Bridge
Contact: geoff.darch@atkinsglobal.com
References
Darch, G.J.C. 2010. Climate change and future flooding in the UK.
PhD Thesis, Climatic Research Unit and Tyndall Centre for Climate
Change Research, School of Environmental Sciences, University of
East Anglia.
Evans, E., Ashley, R., Hall, J., Penning-Rowsell, E.C., Saul, A.,
Sayers, P., Thorne, C.R. and Watkinson, A. 2004a. Foresight.
Future Flooding. Scientific Summary: Volume I - Future risks and
their drivers. Office of Science and Technology, London.
Evans, E., Ashley, R., Hall, J., Penning-Rowsell, E.C., Sayers, P.,
Thorne, C.R. and Watkinson, A. 2004b. Foresight. Future Flooding.
Scientific Summary: Volume II - Managing future risks. Office of
Science and Technology, London.
Jones, P.D., Leadbetter, A., Osborn, T.J. and Bloomfield, J.P. 2006.
River-flow reconstructions and implied groundwater levels. Science
Report SC040068/SR2. Environment Agency, Bristol.
Turner, R.K. 2005. Integrated environmental assessment and coastal
futures. In: Vermaat, J.E., Bouwer, L., Turner, R.K. and Salomons,
W. (eds.) Managing European Coasts: Past, Present and Future.
Springer, Berlin: 255–270.