Download Pre-Workshop scoping document

Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Flood Foresight USA: Scoping Document
Colin R Thorne
Edward P. Evans
Pete Rabbon
University of Nottingham, UK
University of Nottingham, UK
US Army Corps of Engineers, USA
This document should be cited as:
Thorne, C.R., Evans, E.P., and Rabbon, P. (2008) with contributions by Jim Hall,
Robert Nicholls, Jon Parke, Edmund Penning-Rowsell, Nick Reynard, Paul Sayers,
Jonathan Simm, Suresh Surendran, and Jon Wicks (UK Foresight team) and Todd
Bridges, Bill Curtis, Jack Davis, Susan Durden, Jeff Harris, Rolf Olson, Edmond
Russo, Martin Schultz, Eric Thaut and Kate White (US Corps team). Flood
Foresight USA: Scoping Document. Report to the UK Department for Innovation,
Universities and Skills, UK Government Office for Science, UK Foreign and
Commonwealth Office, and US Army Corps of Engineers, based on the Foresight
Mission to Washington DC (September 15-19, 2008), under DIUS Purchase Order
Number 84001054, University of Nottingham, UK, 23p.
Context
The Foresight ‘Future Flooding’ report of 2004 (Evans et al. 2004a and b) in the UK
is an example of scientific research being used to inform policy and decision making
at a national and regional level. The approach and methodologies developed and
applied in the project have elicited interest abroad, leading to seminars in China and
Russia in 2005. The Chinese seminar has led, in turn, to a joint 3-year, Sino-UK
project to examine the future of flood risk in the Taihu Basin around Shanghai that
runs from 2006 to 2009.
In 2007, presentations on the Foresight ‘Future Flooding’ project at technical
meetings of the US Army Corps of Engineers attended by senior personnel and
representatives of the Association of State Floodplain Managers (ASFPM) and the
National Association of Flood and Stormwater Management Agencies (NAFSMA)
stimulated interest in the United States of America concerning the transferability of
the Foresight approach and the possible value of a Foresight ‘Future Flooding’
project in the USA.
To progress the ideas already discussed informally and in a preliminary fashion by
scientists and engineers, a mission was performed by UK scientists and engineers
with experience in flood foresight between September 15 and 19, 2008. The mission
was performed under the auspices of the UK Foreign and Commonwealth Office
(FCO), in particular the British Consulate in Atlanta, and it benefited from
sponsorship by the FCO, the UK Department for Innovation, Universities and Skills
and the UK Government Office for Science. The mission included closed meetings
with USACE scientists and engineers and Corps leadership, and a two-day workshop
attended by US stakeholders and experts in flood risk management from a wide
variety of Federal and State agencies.
The workshop was highly successful and attained all of its goals, and the
presentations made by both US and UK speakers have been supplied to the
sponsors. It was organised by Susan Durden and Jack Davis of the US team and
1
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Kerry Norton and Jon Parke of the UK team. It was thanks largely to their diligent
efforts that the workshop came to fruition.
This document represents the main deliverable generated by the Foresight Mission
and is being supplied to the UK sponsors and the USACE for their use.
Background – Flood risk in the USA
Federal disaster assistance outlays through the Disaster Relief Fund have grown
drastically over the past three decades, increasing from an average annual outlay of
$444M during the 1980s, to an average annual outlay of $3.75B during the past
decade (expressed in constant 2005 dollars). (CRS, 2005).
Flood risk management defines flood risk as:
Flood Risk = f(probability, consequences)
This definition conveys the essential need for a partnership between the agencies, at
all levels, responsible for a wide range of actions relevant to integrated flood risk
management that seeks to manage down the consequences of flooding as well as
reduce its probability of occurrence.
The Foresight ‘Future Flooding’ Project 2004
The Foresight project:


used a structured framework which considered science-based scenarios of
socioeconomic development and climate change to, “provide an indication of
future risks from flooding and coastal erosion.”
looked 30 to 100 years ahead in, “quantifying the possible scale of the
challenges and providing a broad assessment of the different measures
available to reduce future flood risks to acceptable levels.”
It considered two questions:


How might the risks of flooding and coastal erosion change in the UK over the
next 100 years?
What are the options are available for Government and the private sector in
responding to the future challenges?
It yielded two key messages:


Continuing with existing policies is not an option—in three out of the four future
scenarios considered, risk grows to unacceptable levels (Figure 1).
Risk needs to be dealt with on a broad front—“we must either invest more in
sustainable approaches to flood and coastal erosion management or learn to
live with increased flooding.”
2
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Figure 1. Annual Expected Damages due to flooding increase to unacceptable levels
in three out of four future scenarios, with particularly significant increases in risk at
the coast and in the major river floodplains by the 2080s.
The techniques and the ability to bring out these credible, easily understandable
messages to senior, key stakeholders, in language which they found useful, was one
of the most important achievements of the project. This is evidenced by the
incorporation of the Foresight messages in UK FRM policy, UK land use policy, new
research projects in key areas and a doubling of UK Treasury investment in
integrated flood-risk management (IFRM) funding (Figure 2). Further proof lies in the
durability of the messages. For example, following catastrophic UK flooding in
summer 2007, Sir Michael Pitt (Pitt 2008) funded updating of the Foresight FCD
project as part of a UK Cabinet Office review of lessons learned in the UK from the
flood events (Evans et al. 2008).
3
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Figure 2. Examples of the many policy and planning documents and studies that
have followed from the Foresight ’Future Flooding’ Project (2004).
The US Backdrop
Floodplain Management 2050 (ASFPM 2008)
The theme of the 2007 Gilbert F. White National Flood Policy Forum was very
relevant to Foresight issues in that it considered how flood risk in the USA might look
in 2050. The main findings were:

 The U.S. is facing unprecedented change, increasing flood risk, and loss of
natural systems.
 Gilbert F. White’s “Human Adjustment Factors” are still relevant to flood risk
management but require expansion.
 Specifically, additional factors should be explored related to:
 Room for rivers and oceans.
 Personal responsibility.
 Geographic interdependencies.
 Awareness and education.
 There is a real need to evaluate U.S. risk and modify policy to meet the
demands of 2050.
USACE Flood Risk Management Program
4
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Vision: To lead collaborative, comprehensive and sustainable national flood risk
management to improve public safety and reduce flood damages to our country.
Mission: To integrate and synchronize the ongoing, diverse flood risk
management projects, programs and authorities of the US Army Corps of Engineers
with counterpart projects, programs and authorities of the Federal Emergency
Management Agency (FEMA), other Federal agencies, state organizations and
regional and local agencies.
Congressional Direction
2008 Appropriations Act
The Energy and Water Development and Related Agencies Appropriations Act, 2008
requires a study to identify any procedural or legislative changes that may be
warranted to allow the Corps of Engineers to be more effective in working with other
Federal agencies, states and local governments and stakeholders in the
management of flood risk.
Water Resources Development Act of 2007, Section 2032
This act includes the direction that:
… the President shall submit to Congress a report describing the vulnerability to
damage from flooding, including the risk to human life; the risk to property; and the
comparative risks faced by different regions of the United States.
It further states that:
…the report shall include an assessment of the flood risk reduction programs; the
extent to which those programs may be encouraging development and economic
activity in flood-prone areas; recommendations for improving those programs with
respect to reducing and responding to flood risks; and proposals for implementing the
recommendations.
Potential for a US Foresight-style project on future
flood risks and their management
Purposes
The purposes of a Foresight-style project on future flooding would include:



Assist in creating a better future by improving our capability to deliver IFRM
that is cost effective and sustainable.
Retain the focus of the UK Foresight project in substantiating and delivering
the key message that if we invest more wisely in IFRM and start now, we will
save money and reduce loss of life through flood damage reduction programs
in the future.
Describe current national flood risk and its regional distribution across the
nation.
5
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008

Generate future scenarios for national flood risks in 2050-2100 under a base
line condition of ‘business as usual’.
Identify and examine options for flood damage reduction measures that could
be used to respond to the increased risks under future scenarios.
Explore the sustainability of possible flood risk reduction measures for 2050 to
2100 in terms of economic costs and benefits, environmental protection and
social justice.
Present the results in graphics, maps and key messages which are easily
accessible to decision makers, policy makers, FRM professionals,
stakeholders and the public.



Output criteria
It is very important that, from the beginning, everyone involved in the project, from
the leader of the high level steering group to the most junior modeler, is fully aware of
the criteria for the outcomes which will be produced through the project. These
criteria include:










Value added
To the nation by creating a better, more sustainable future
Study cost must be justified by the savings in flood damages
Intergovernmental value
- Outcomes involve and are acceptable to all government agencies with FRM
nexus
Durability
- Long useful life
- Easy to update
Alignment
- USACE programs (for example, Actions for Change and Wise Use of
Floodplains)
- Federal partners’ strategic plans
- Next administration’s agenda
Coordination
- Administration
- Congress
- States
- Local governments
Collaboration
- Stakeholders
- Externally
Cost effectiveness
- Analysis commensurate with the required detail of output
Timeliness
- Leverage the present visibility of flooding
- Deliver outcomes in time for uptake to be effective in FRM by 2050
Independency
- Impartial
- Objective
- Credible
Visionary
- Innovative thinking
- Longterm perspective
-
6
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
In conceiving a possible Foresight ‘Future Flooding USA’ project, maximum use will
be made of relevant ongoing research and study programs such as the Great Lakes
IOC study, which includes futures work and flood risk reduction.
Setting up the project – partners, stakeholders,
contributors and project team
The UK FCD project employed a carefully designed project structure. A fundamental
principle of this was to fully engage key policy-level partners and stakeholders in the
broader flood-related community, convince them of the relevance of the study’s key
findings and to inform their actions. The UK partnership set up is shown in Figure 3
below as starting point for a possible US Foresight project:
Ministerial
Stakeholder
Group
GCSA &
Sponsor
Minister
GOScience
team
Expert
Advisers
Science
Advisers
Government
Departments
Civil Society
UK and
International
Experts
Figure 3. Partnerships in the UK Foresight ‘Future Flooding’ Project (2004).
US partnering arrangements are bound to be different, and one of the most important
initial tasks in any US Foresight project will be to set up the partnership and a
communication packages in ways that will ensure that the stakeholders are fully
involved and that key messages will be carried over into policy at least as well as
they were in the UK. This corresponds to the concept of shared–vision planning.
USACE activities will reduce future flood risk, but it will be essential also to consider
the actions of other agencies. This will be part of the framework for assessing the
effectiveness of alternative FRM options and long term strategies. As the scope of a
Foresight project is much broader than engineering, it will be necessary to define
clearly the role of the USACE in the project and avoid any false appearance of
mission creep. Also, it will be necessary to demonstrate that the project will be
independently led and will be based on development and analysis of the best
available scientific evidence.
In the UK the project was led by the Office of Science and Technology (now the
Government Office for Science) and spanned the department of government
7
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
responsible for flood risk policy (Department of Food and Rural Affairs - Defra), its
operating agency (the Environment Agency), the department responsible for land use
planning (Communities and Local Government), and the Her Majesty’s Treasury.
Technical approach
The analytical framework
The flooding system encompasses the physical and human systems that influence or
are influenced by flooding. The 2004 project considered the flooding system in two
elements: river and coastal flooding occur where water invades inhabited or
developed areas from watercourses and the ocean; “intra-urban” flooding arises from
rainfall events within urban areas that overwhelm the urban drainage system. Clearly,
the flooding system involves many flooding mechanisms, and is illustrated by the
system diagrams (Figure 4) reproduced below from the 2004 reports.
Figure 4: The flooding system. Upper image: river and coastal flooding system.
Lower image: intra-urban flooding system (from Evans et al., 2004a).
In 2004 the terms ‘drivers’ and ‘responses’ were used for things that change the
flooding system and, hence, future flood risk. They are illustrated in Figures 5 and 6.
By definition:
Drivers – are phenomena that may change the state of the flooding system, such as
climate change, urbanisation or changing agricultural practices, and
8
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Responses – are measures implemented in order to reduce flood risk.
The distinction between drivers and responses is not always crisp; some drivers are
under the control of flood managers and can, under some circumstances, be used as
responses to rising flood risk. Conversely, responses can themselves become drivers
in other circumstances – for example, the use of engineered flood defences to
reduce flood risk in one town may adversely affect flood risk downstream and will
therefore be a driver of flood risk in another town.
Figure 5: Drivers and Responses, showing the degree of control for different drivers:
drivers towards the right can be used as responses to flood risk.
Drivers
Phenomena that change the state of the
system
System state variables
Sources
Pathways
Receptors
rainfall
sea level
marine
storms
etc.
urban surfaces
fields, drains
channels
flood storage
flood defences
floodplains
people
houses
industries
infrastructure
ecosystems
• .
System
analysis
Impacts (Risk=
Probability x
Consequences)
(economic,
social,
environmental )
Responses
Changes to the flooding system that are
implemented to reduce flood risk
Figure 6: Relationship between drivers, responses and flood risk.
The 2004 Foresight study in the UK used a Source-Pathway-Receptor (SPR)
framework in analysing the drivers and responses (Figure 6). Climate change and
socioeconomic development scenarios were used to provide the backdrop for
assessing possible UK flood risk between 2030 and 2100. The scenarios were
combined into pairs (Figure 7) to provide alternative sets of parameters for climate,
economics and society in different possible futures.
9
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Figure 7: Combined climate change and socio-economic development futures used
in the 2004 Foresight ‘Future Flooding’ analysis for the UK.
The climate change scenarios were based on the report of the UK Climate Impacts
Programme, UKCIP02 (Hulme et al. 2002) and the socio-economic scenarios were
taken from the Social Policy Research Unit (SPRU) ‘futures’ work (SPRU et al.,
1999), which was based on the Intergovernmental Panel on Climate Change (IPCC)
Special Reports on Emission (SRES) scenarios.
The 2004 study demonstrated that a Source-Pathway-Receptor (SPR) model of the
flooding system can be used as a logical framework around which to build an
analysis of future flood risks a long way into the future.
At the Foresight Workshop in Washington DC, FRM scientists and engineers from
the US and UK were fully briefed on the 2004 study outlined above and they
discussed how a similar project might be performed in the USA. In the remainder of
this section we present an overview of the possible technical approaches that
emerged at the workshop. The project could be performed in three main work
packages (Figure 8) each of which is described in outline in the following sections:



Scenario creation
Conceptual model and Expert Assessment
Flood Risk Modeling and Assessment
10
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Scenarios
Conceptual model / expert elicitation
Weight of
evidence
Outputs and key
messages
Modeling
Figure 8. Main elements of a possible Flood Foresight US Project
Developing Scenarios for future flood risk assessment
What is a scenario?
Scenarios are a way to structure, think about, and plan for, future uncertainties. This
approach requires the articulation of more than one possible future (typically three or
four). Scenarios do not predict the future. Rather they provide the means to
consider today’s policies and their robustness, and decision-making processes in
light of potential future developments. In this context, Foresight UK has developed a
‘Futures Toolkit’ available on the Foresight website which describes a number of
futures techniques and how they might be used:
http://hsctoolkit.tribalctad.co.uk
A scenario is a description of potential future conditions and not a forecast. Some
people describe them as ‘storylines’, to emphasize the fact that they may or may not
be the result of modeling. However they are based on hard information on realistic
future trends, complemented by expert judgment.
Scenarios help us to inform decisions that involve high stakes but poorly
characterized uncertainties. The use of scenarios allows us to identify meaningful
changes so that we can adapt as appropriate, as the future unfolds. This is
particularly relevant when we are looking several decades ahead, as uncertainty is
inherent in this kind of forward thinking. In this context, socio-economic modeling, in
particular, is not generally possible more than about two decades into the future (if
that) making the use of scenarios essential if we are to develop foresight that extends
beyond such short horizons.
11
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
The use of scenarios is not new, and these approaches are now universally accepted
for assessments embracing possible changes across a range of possible futures and
within multiple applications and domains. They are used in all areas of government,
as well as in the private sector. For example, the Rand Corporation was one of the
leaders of this type of work in the 1970s and 80s. Indeed, it is no exaggeration to say
that scenario analysis is now a “mainstream” method.
This application will focus on flood risk and its management, although due account
will be taken of a broad range of changes in socioeconomics, climate and the
environment as they affect water resources and their management more generally.
Why do we need scenarios?
Flood losses have been increasing in recent decades. Many stakeholders believe
that they will continue to grow to evermore unacceptable levels unless steps are
taken to reduce future risks. We need to use futures work and scenario analyses to
give us forward vision of how risks may increase so that we can ensure that flood risk
reduction measures can be identified and implemented in time to prevent this.
The US economy and society are changing rapidly in multiple ways and these
changes will have profound influences on future flood risks. Some examples of
changes are a growing population and an expanding economy, with the strongest
trends occurring in the South and West of the nation. Much of the growth in
population and wealth is happening in the floodplains.
At the same time, we are observing changes in climate, relative sea levels and
watershed, river and coastal environments at the national and regional scales (e.g.,
Zhang et al., 2000). The consensus amongst the scientific community nationally and
internationally is that these changes are expected to continue and, in many cases,
intensify through the remainder of the 21st Century. There are, however, significant
uncertainties about the implications for extreme weather events and the floods they
generate. For example, there is a debate between US scientists about the possible
future intensification of hurricanes. While the implications remain uncertain, climate
change would have major implications for national and regional flood risks.
Faced with multiple uncertainties concerning socio-economic and climate futures, a
range of consistent and coherent scenarios accounting for changes in socioeconomics, climate and relative sea-level, and other relevant environmental
parameters are required to develop an internally consistent and coherent set of
possible futures. These scenarios are also used to reference future conditions to the
current situation (usually termed the “baseline”).
The scenario approach adds value to all stages of the assessment of future flood
risks as follows:



The development of the scenarios by the project team and with the partners
and stakeholders develops a coherent and shared vision of possible futures;
Once agreed, the scenarios provide a shared vision of a range of futures that
provide benchmarks for the assessment;
The scenarios assist communication of complex issues of future change to a
wide audience of stakeholders, including the results of expert knowledge
elicitation (qualitative assessment) and modeling (quantitative assessment)
with respect to future flood risks.
12
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Scenario Development
The development of the scenarios would involve four steps as follows:




Review the existing work on futures across all the scenario dimensions (socioeconomic, climate and environment);
Select the key scenario dimensions (as an example, in the UK 2004 Foresight
study, the key dimensions were governance, societal attitudes and values, and
greenhouse gas emissions (Evans et al., 2004) – but many other dimensions
can be considered);
Group/classify a small number of consistent sets of scenarios which describe
future variability within the scenario space;
Consult widely with partners and stakeholders to ensure that the scenarios
selected are credible and widely accepted (note that this consultation would be
ongoing).
The consultation step inevitably means that scenario development would be iterative,
and there will be widespread discussion and agreement on the selected scenarios as
the project proceeds. The parameters that would be considered would be defined by
the scenarios considered relevant to the expert assessments and quantitative
modeling (Figure 8).
Data Sources required for Scenario Development
Scenario development for flood risk assessment uses a diverse set of data on
observed trends, and possible future trends. For socio-economic changes, our ability
to predict the future is rather limited compared to climate and environmental changes
and this influences the data sources and the methods we use. Hence, socioeconomic and climate/environmental scenarios are discussed separately.
Socio-Economic Scenarios
We would examine a range of nationally-available data and existing scenario
analyses. Example datasets of relevance to flood risk assessment include historic
and present:



National census data;
National and regional economic data;
National property distribution.
We would also look at the relevant national forecasts, such as those for population
and urbanization, recognizing that many of these may be rather short-term compared
to the 2050 to 2100 time frame of the study. However, they provide important
information on likely near-term trends, which the scenarios should reflect and use to
the maximum degree possible.
Lastly, we would use peer-reviewed sources on national futures such as the US
Climate Change Science Program Product 2.1b (Parsons et al., 2007).
Climate and Sea-Level Rise Scenarios
We will use existing data sources for observed and future climate and sea-level
changes, particularly the databases produced as part of the Intergovernmental Panel
on Climate Change (IPCC) Fourth Assessment Report (AR4). For key climate
parameters such as temperature and precipitation, the IPCC (Meehl et al., 2007)
conducted a global coupled climate model experiment producing a “multi-model data
13
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
set” for up to 23 global climate models (GCMs), including projections to 2100 under
three IPCC SRES (Special Report on Emission Scenarios) emission scenarios
(Nakićenović and Swart, 2000). National assessments and related climate data will
also be considered, especially downscaling efforts. For relative sea-level rise, the
global scenarios will also be used, with inclusion of regional and uplift/subsidence
components (see Environmental Change Scenarios below). Not all of the climate
factors relevant to flood risk assessment are well defined, but at the same time, they
should not be ignored. For these factors, such as hurricane intensity, some debate
will be required on the scenarios that are used: for instance, a no change and an
increase scenario could be considered to reflect the currently high uncertainty
concerning the frequency and intensity of future extreme weather phenomena.
As an example of the type of detailed scenario analysis that is possible for factors
consider in detail by Meehl et al. (2007), Figure 9 shows the relative percentage
changes in winter and summer precipitation across the globe. The blue areas
indicate increases by the final decade of this century relative to the period 1980-99.
The stippled areas show those parts of the globe where 90% of the GCMs used in
the multi-model analysis agree with the sign of the seasonal change.
Figure 9: Relative percentage changes in precipitation for the period 2090–2099,
relative to1980–1999. Values are multi-model averages based on the SRES A1B
scenario for December to February (left) and June to August (right). White areas are
those where less than 66% of the models agree in the sign of the change and
stippled areas are where more than 90% of the models agree in the sign of the
change (Meehl et al., 2007)
These IPCC data sources can be used to illustrate the spread of the potential climate
changes for the USA. For example, Figure 10 shows indicative changes for rainfall
and temperature for the USA during the winter under 3 emissions scenarios. Each
dot represents one GCM result. The boxes represent change under each of these
three future emissions scenarios.
Environmental Change Scenarios
Environmental changes that influence flood risk will also be considers as appropriate.
Key factors are:
14
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008




land uplift (e.g., Alaska) or subsidence (e.g., coastal Louisiana and east
Texas) which influence relative mean and extreme sea levels;
changes in land cover which will influence run-off characteristics;
coastal and river morphology changes, such as the widespread erosive trends
observed in the lower 48 states, and more recent issues in Alaska;
variations in seismicity which can contribute to dike failure (and also influence
land levels in coastal areas – see above).
Figure 10. Winter changes in precipitation and temperature for the USA. The dots
represent the IPCC AR4 scenario changes from all GCMs. The boxes show the
scenario space under three of the SRES emissions scenarios: B1, A2 and A1B.
Scenario Synthesis
The diverse set of scenarios proposed here will provide:



A framework and a discipline for expert knowledge elicitation and qualitative
assessment of future changes in flood risks.
A structure to drive and guide quantitative modeling of future flood risks.
A method for reporting complex results in a coherent and accessible manner.
To develop our scenarios, there are five key steps that we need to follow:



We need to run the national quantitative flood risk impact model (maybe at
prototype stage) across all the combinations of socio-economic and climate
changes, using selected impact metrics.
The results need to be characterized as a range of possible impact changes
(i.e. an array of possible future flood risk impacts).
From this array we select a manageable number of model runs that cover the
full range of impact space. These will be the basis of selection of the scenarios
to be examined in detail.
15
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008


The next step is to ‘unpack’ the storyline behind each of the selected results:
what are future climates, economies and societies like in these cases? The
results will be quantitative data on the parameters that describe selected
combinations of climate (rainfall and temperature), economy and society (e.g.
GDP; population growth and structure).
We will then consult partners and stakeholders on these scenarios (and out
process developing them) to get “buy in” at this stage.
Outputs and high level messages
This first element of the project will add value and produce important insights and
outputs. It will define the wide range and magnitudes of possible future flood risks
under multiple combinations of scenario parameters. It will further facilitate
discussion between the project team and its partners and stakeholders about which
scenarios to take forward for more detailed flood risk assessment, and enable the
team to tailor these to partner and stakeholder needs and focuses.
Expert Assessment
Context
Expert knowledge elicitation and assessment will link the future scenarios to the
quantitative modeling. Multiple lines-of-evidence will be assembled into a weight of
evidence generating results and conclusions, as shown in Figure 8. The approach
will be deliberative and advanced, using a group of experts, and it will be linked to the
modeling process as described in the next section.
Objectives and value of outcomes
A conceptual model, with sets of drivers and potential responses (flood damage
reduction measures) as inputs, will be used to understand how the flood risk system
could change in future. The drivers of future changes in flood risk and the flood risk
reduction measures that could be used in response to future increases in flood risk
will be identified and described in detail, including:




a clear definition,
a commentary on how the driver or measure operates and interacts with other
drivers and measures,
identification of regional variability, and
a full description of uncertainties.
Case examples will be provided, along with a short bibliography focused on
authoritative references and sources from the peer reviewed literature.
Cause-effect diagrams will explain the relationships between drivers and measures
including their interactions. An assessment of the impacts of drivers and flood risk
reduction measures on future flood risks will support scoring and relative rankings of
drivers and measures in terms of their potential to change future flood risks. This will
include consideration of the sustainability of options for flood risk reduction, in terms
of cost-effectiveness and environmental justice.
16
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Data resources acquisition and approach
Required critical data will be identified, inventoried, and organized for use in the
expert assessment process. It is recognized that the availability and quality of data
varies between regions and watersheds across the United States. Due account will
be taken of this in the expert assessment, with the assessment focused on areas and
regions where the population is denser, property and infrastructure is concentrated
and flood risks are higher.
In order to achieve buy-in, experts must be selected from across a diversity of
important partners and stakeholders (e.g., federal, state & local agencies, private,
academia, and non-governmental organizations). Experts will be selected on the
basis of their national esteem, credibility among peers, diversity of technical and
geographical experience, and knowledge, skills, and abilities to envision change in
the flooding system.
The expert group may require supporting sub-groups to elicit specialist knowledge
and handle geographical variability in the importance of different drivers and
measures. Dynamic peer review will be required at each step, which may result in
inclusion of additional experts to the extent necessary.
Process advancement
Formally recognized and agreed procedures of expert knowledge elicitation will
require organization of activities and workshops with a view towards arriving at
consensus (buy-in). Sub-group workshops may be held to address special topics
and geographical issues. Agreement on risk metrics (e.g. economic damages,
people/property at risk, environmental consequences of floods) must be attained to
promote interactions with the quantitative modeling. The key interactions with the
modeling work package (see Figure 8) will include:


Provision of estimated potential changes in the variables for use in the
quantitative model.
Comparison of results from sensitivity analyses performed in the quantitative
modeling with those determined by expert elicitation, thereby identifying
influential drivers for comparison with expert estimates.
The work will be managed under a strict timetable to maintain the energy and focus
of the study.
Outputs and high level messages
The conceptual model of the flood risk system (source-pathway-receptor) will be
enabled through development of a shared understanding of drivers, their interactions,
and relative importance (i.e. rankings). The goal is generation of consensus on the
problem, assisted by structured deliberation, to generate the weight of evidence
needed on the potential for application and sustainability of future alternative
portfolios of flood risk management measures under each selected future scenario.
Compared with the UK, the USA is both larger and more diverse, which presents a
challenge in terms of representing regional variations and contrasts while not losing
sight of the national and strategic messages. This will require an excellent
communication plan and carefully targeted use of graphics and maps.
17
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Quantitative Model Based Assessment
Objectives
A quantified, model-based assessment of flood risk at a national scale would be
performed in the third work package to answer the following questions:



What is the magnitude of current flood risk on a national scale and where are
the hot spots? From the assessment, visual results will provide a depiction of
the entire US and will show how risk varies across the lower 48 states.
How might climate and socio-economic change influence flood risk on a
national scale? The assessment will quantify the potential future changes in
flood risk due to the effects of drivers, including climate, socio-economic and
environmental change. The results will be provided for the period 2050 to
2100.
How effective are alternative measures and policies for flood risk reduction
and what are the benefits? The assessment will quantify potential for reducing
flood risk in the future by implementing flood risk reduction alternatives to
reduce the increases resulting from climate, socio-economic and
environmental factors to acceptable levels.
As well as providing quantified evidence for the Foresight ‘Future Flooding USA’
study, the assessment may be used to support the commitment for reporting on flood
risk that is included in the Water Resources Act 2007, Section 2032.
Modeling approach
The proposed quantified assessment would operate at the national scale and would
be based on available, national datasets. It will, therefore, necessarily be broad scale
and should not be employed for local flood risk assessment and strategy
development. Given the heterogeneity of human habitation and development in the
USA, it may be appropriate to adopt a two-tier approach that focuses most effort in
regions where people, property, infrastructure and flood probability are concentrated,
whilst using more approximate methods where flood probability is low and/or the
consequences of flooding are low, resulting in flood risks that are less significant.
The results should nevertheless be demonstrably robust and, in the present day
assessment, be consistent with the average scale of flood losses that have been
experienced in recent years.
The national flood risk assessment method will incorporate a high level
representation of the river and coastal flood risk systems, including the:




Probability of flooding – reflecting extreme loads, levee performance (strength
and standard) and floodplain topography/flood spreading.
Risk to life – reflecting flood depth, water speed and population density and
structure.
Flood damages – reflecting economic development, property type and value,
population demographics and environmental characteristics.
It is proposed to run the quantified assessment for the present day (providing
the baseline for the assessment of change) and then alter the variables within
the model to represent the future change envisaged under the various socioeconomic, climate, environmental and flood risk management futures,
including:
18
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008


Drivers – including changes to rainfall, runoff, river flows, extreme sea levels,
floodplain occupancy, the relationships between flood depth and property
damage, levee deterioration and land use change.
Responses - flood risk management measures and policies – including levee
strengthening and raising, floodplain development control, warning and
evacuation, flood proofing and resilience, insurance etc.
The high–level method, using data of this type, as employed in the UK in 2004 does
not require explicit hydrological or hydraulic modeling, making it feasible at the scale
of the lower 48 states of the USA.
Some examples of how future changes and flood risk management policies may be
included in the assessment model are listed in Table 1.
Table 1: Examples of representation of future changes in the risk assessment model
Future change
Suggested implementation in flood risk
assessment model
Drivers of future change
Increasing development in floodplain
Variation in number/area of building in the risk
model
Changing value of floodplain buildings Variation in depth-damage curves
and contents
Changes in rainfall
Variation in fluvial flood frequency (from existing
climate impacts model studies)
Sea level rise
Variation in coastal flood frequency
Levee deterioration
Variation in fragility curves
Flood risk management policies
Floodplain development control
Variation in number/area of building in the risk
model
Levee raising
Variation in frequency of overtopping
Levee strengthening
Variation in fragility curves
Flood proofing
Variation in depth-damage curves
Changes in insurance arrangements
Variation in proportion of economic losses that are
insured
The aim will be for the risk assessment model to be run a large number of times, in
order to explore flood risks associated with the selected range of future scenarios. It
should also be possible to undertake sensitivity analyses using the model, in order to
provide quantified evidence of the significance of the drivers, to complement the
qualitative expert assessment performed in the previous work package.
Data sources
The modeling methodology is dependent upon the existence and quality of relevant
datasets and will be customised so that it can make use of the datasets available. A
preliminary scoping of datasets has identified the following relevant datasets, which
provides some grounds for confidence that the necessary data are in fact available:



Digital Elevation Data (USGS).
Floodplain mapping from the map modernization program (FEMA).
Land Use/Land Cover (NRCS).
19
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008







Coastal Water Levels (NOAA).
Precipitation Frequency data (NOAA, Local).
Rating Curves (USGS, USACE).
Census/Population data (HAZUS, Census).
Insurance Claims.
Levees information (USACE)
Existing Study Results (Federal and State partners)
Proposed methodology for the flood risk assessment
The quantitative assessment would be implemented through the following steps:
Step 1 – Specification
Through interaction with the expert assessment team, we would draw up a
specification of the key flood causing processes, as well as drivers and responses
(risk reduction measures) that need to be included in the quantitative model-based
assessment. Some of these will be explicitly included in the quantitative model,
whereas others will need to be included through the use of surrogates.
Step 2 – Obtain data
We would draw together the datasets needed to support the assessment. These
datasets need to be available as spatially referenced, digital data. It is acknowledged
that there will not be 100% geographic coverage and therefore sensible default
values will need to be defined.
Step 3 – Finalise method/model
At the same time as we bring the datasets together, we would formalise the definition
of the flood risk assessment methodology. The method would be described using
flowcharts and algorithms. The computer model would be established at this stage.
The method would be implemented as software code with a focus on sufficiently
accurate representation of the method and efficiency of calculation. The software will
be designed to make use of the high throughput computing environment available to
the USACE.
Step 4 – Define method for incorporating change
In association with the expert team, the representation of the key drivers of change
and flood risk management responses within the model would be documented.
Step 5 – Verification
The methodology and software would be piloted on a selected region (such as a
moderately-sized basin or coastal cell). This would enable the software
implementation of the method to be verified (checking the software and data
transformations) and non-functional attributes, such as run times, to be assessed.
Some optimisation of the software and/or data pre and post processing modules may
be necessary at this time.
Step 6 – Validation
The pilot application would be undertaken in a region where other studies or actual
flooding incidents have provided data on flood impacts. We would compare the
outputs of the pilot application to the other estimates of flood impacts (from previous
studies and records of flood losses) in order to assess whether the method produces
20
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
results of appropriate accuracy. If results are not sufficiently accurate we will need to
consider changing the method and/or data.
Step 7 – Baseline assessment
The baseline assessment will involve the calculation of the risk metrics for the nation
for current day conditions. This would be relevant to the Water Resources
Development Act of 2007, Section 2032.
Step 8 – Future scenarios and responses
The variables in the risk model would be modified to represent the potential effect of
future changes, for example due to climate or socio-economic changes. The model
would also be used as a platform for testing the effectiveness of flood risk
management measures and policies in reducing future flood risks. The model would
be used to examine a range of different scenarios and to explore the influence of
future uncertainties. Sensitivity analyses would be conducted to test the relative
importance of future drivers. Risk metrics would be calculated and presented at a
scale appropriate for a national scale flood risk assessment.
Outputs
The primary outputs from the assessment (for both present day and future scenarios)
would include:




Expected Annual Damages (economic, $).
Number of people exposed to a high probability of flooding (disaggregated for
different population sectors).
Number of properties exposed to a high probability of flooding.
Other outputs could be extracted from the model where considered useful,
such as the change in insured losses under different future scenarios.
The results would be presented as national aggregated figures. These could also be
disaggregated regionally, according to flooding processes (coastal or river), or by
societal type. The presentation of the results would include maps, graphs and tabular
outputs.
Next Steps




Convert this initial scoping document to an outline proposal, including draft
governance and program structure.
Vet internally.
Establish external partners.
Obtain Administration support and direction to move forward.
References
Dawson, R.J., Hall, J.W., Bates, P.D. and Nicholls, R.J. (2005) Quantified analysis of
the probability of flooding in the Thames Estuary under imaginable worst case sea
level rise scenarios. International Journal of Water Resources Development, 21,
577–591.
Evans, EP., Ashley, R., Hall, J., Penning-Rowsell, E., Sayers, P., Thorne, C. and
Watkinson, A. (2004) Foresight Future Flooding, Volume I and Volume II. Office of
Science and Technology, London.
21
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
Evans, E.P., Hall, J. W., Penning-Rowsell, E.C., Saul, A., Sayers, P.B., Thorne, C.R.
and Watkinson, A.R., 2006. Drivers, responses and choices for future flood risk
management. Proceedings ICE, Water Management 159, March 2006, pp 53-61.
Evans, E.P., Simm, J.D., Thorne, C.R., Arnell, N.W., Ashley, R.M., Hess, T.M., Lane,
S.N., Morris, J., Nicholls, R.J., Penning-Rowsell, E.C., Reynard, N.S., Saul, A.J.,
Tapsell, S.M., Watkinson, A.R., Wheater, H.S. (2008) An update of the Foresight
Future Flooding 2004 qualitative risk analysis. Cabinet Office, London.
Hall, J.W., Dawson, R.J., Sayers, P.B., Rosu, C., Chatterton, J.B. and Deakin, R.
(2003) A methodology for national-scale flood risk assessment. Water and Maritime
Engineering, 156(3), 235–247.
Hulme, M., Jenkins, G. J., Lu, X., Turnpenny, J. R., Mitchell, T. D., Jones, R. G.,
Lowe, J., Murphy, J. M., Hassell, D., Boorman, P., McDonald, R. and Hill, S. (2002).
Climate Change Scenarios of the United Kingdom: The UKCIP02 Scientific Report.
Tyndall Centre for Climate Change Research, School of Environmental Sciences,
University of East Anglia, Norwich, UK.
Meehl, G.A., T.F. Stocker, W.D. Collins, P. Friedlingstein, A.T. Gaye, J.M. Gregory,
A. Kitoh, R. Knutti, J.M. Murphy, A. Noda, S.C.B. Raper, I.G. Watterson, A.J. Weaver
and Z.-C. Zhao, 2007: Global Climate Projections. In: Climate Change 2007: The
Physical Science Basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change [Solomon, S.,D. Qin, M.
Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)].
Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
Nakićenović, N., and R. Swart (eds.) (2000). Special Report on Emissions Scenarios.
A Special Report of Working Group III of the Intergovernmental Panel on Climate
Change. Cambridge University Press, Cambridge, United Kingdom and New York,
NY, USA, 599pp.
Parson E, Burkett V, Fisher-Vanden K, Keith D, Mearns L, Pitcher H, Rosenzweig C,
Webster M (2007). Global change scenarios: their development and use. A report by
the U.S. climate change science program and the subcommittee on global change
science research. Product 2.1b Department of Energy, Office of Biological
Environmental Research, 102p.
Pitt, M (2008). Lessons learned from the summer floods of 2007. Cabinet Office,
London, UK, 505p.
SPRU (1999) Socio-economic futures for climate impact assessment: Final Report.
Science Policy Research Unit, University of Sussex.
Thorne, C.R. Evans, E.P. and Penning-Rowsell, E.C. 2006, Future flood and coastal
erosion risks. Thomas Telford, London
Zhang, K. Q., Douglas, B.C. and Leatherman, S.P. 2000: Twentieth-century storm
activity along the US east coast. Journal of Climate, 13, 1748-1761
22
Foresight ‘Future Flooding USA’ Workshop: Washington DC, 15-19 September 2008
23