9 may 2011 future flooding in the eden: frameworks and models geoff darch atkins (and climatic...
TRANSCRIPT
9 May 2011
Future flooding in the Eden:Frameworks and models
Geoff Darch
Atkins (and Climatic Research Unit and Tyndall Centre, University of East Anglia)
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 challengeThe 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 floodingMonthly 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: receptorsChange in peak flow at selected receptors for the 2080s compared to the three historical events under different scenarios
Results: receptorsChange 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
Options
Preferred options
Scenarios
Options
Sensitivity / impact domain
Impact models
Preferred options
A simple comparison of scenario- and sensitivity- led approaches
Alternative frameworks
Other alternative frameworks!
Policy-led Resilience
Scenarios
Sensitivity / impact domain
Options
Preferred options
Impact models
Preferred options are those which deliver resilience to pressures; resilience can be precautionary (e.g. design to maximum likely pressure) or non-specific (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)
ReferencesDarch, 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.