Transcript occurrence of floods - e-Institute

Cities and
Flooding
A Guide to Integrated
Urban Flood Risk
Management for
the 21st Century
WBI e-institute Webinar,
3 April 2012
Urban flooding is a serious and growing
development challenge
IBRD 38919 NOVEMBER 2011
• The occurrence of floods is the most frequent among all
natural disasters globally. In 2010 alone, 178 million people
were affected by floods. The total losses in exceptional years
such as 1998 and 2010 exceeded $40 billion. Flood events, 1970-2011
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Rome Wasn’t Built in Day..
China Does it in Two
Weeks!
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A forward looking approach:
Integrated Urban Flood Risk Management
• Operational guidance on how to manage the
risk of floods in a quickly transforming urban
environment and changeable climate.
• Over fifty case studies, a series of “how-to”
sections and a set of guiding policy principles,
illustrate the state-of-the art on integrated
urban flood risk management.
• Comprehensive and user-friendly, the Guide
serves as a primer for decision and policy
makers, technical specialists, central, regional
and local government officials, and concerned
stakeholders in the community sector, civil
society and non-governmental organizations,
and the private sector.
• Website: http://www.gfdrr.org/urbanfloods
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12 guiding policy principles
1. Every flood risk scenario is different: there is no flood management blueprint.
2. Designs for flood management must be able to cope with a changing and uncertain
future.
3. Rapid urbanization requires the integration of flood risk management into regular
urban planning and governance.
4. An integrated strategy requires the use of both structural and non-structural measures
and good metrics for “getting the balance right”.
5. Heavily engineered structural measures can transfer risk upstream and
downstream.
6. It is impossible to entirely eliminate the risk from flooding.
7. Many flood management measures have multiple co-benefits over and above their
flood management role.
8. It is important to consider the wider social and ecological consequences of flood
management spending.
9. Clarity of responsibility for constructing and running flood risk programs is critical.
10.Implementing flood risk management measures requires multi-stakeholder cooperation.
11.Continuous communication to raise awareness and reinforce preparedness is
necessary.
12.Plan to recover quickly after flooding and use the recovery to build capacity.
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Understand the flood hazard and the impact
• Understanding hazard requires better
comprehension of types and causes of
flooding, probabilities and occurrence.
• Invest in producing and making
widely accessible risk data! Invest in
preparedness and response:
– Flood hazard maps are visual tools
for communication the hazard situation
in an area.
– Flood forecasting is an essential tool
to provide people exposed to risk
advance notice of flooding in an effort
to save lives and property.
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Climate Change and Flooding
“Projected changes in climate extremes under different
emissions scenarios generally do not strongly diverge in
the coming two to three decades, but these signals are
relatively small compared to natural climate variability
over this time frame. Even the sign of projected changes
in some climate extremes over this time frame is
uncertain.”
-IPCC Special Report on Managing the Risks
of Extreme Events and Disasters to Advance Climate
Change Adaptation
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Make Decision-making More Robust
• Forget about optimal
design and anticipating
all risks
• Traditional cost-benefit
analysis does not work
when dealing with
catastrophic “tail” risk.
• Instead focus on “robust”
design, invest in data,
preparedeness and
response.
• Develop robust indicators
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ALARP Principle
ALARP Principle
Source: Ranger and Garbett-Shiels, 2011, LSE
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Get the Balance Right Between
‘Structural and Non-structural Measures
• Structural and non-structural measures do not preclude each other.
Most successful strategies combine both types, striking the right balance
between them.
• Structural measures: Keeping the water away from the people
– Are seen as less flexible, but flexibility can sometimes be
incorporated, such as in the installation of wider foundations for flood
defenses so that they can be raised later without strengthening the
base. The purchase of temporary flood defense barriers can also be
seen as a flexible alternative as they can be deployed when and
where necessary, as flood risks change
• Non-structural measures: Keeping the people away from the water
[often has large co-benefits]
– Many non-structural measures tend to be inherently flexible, e.g.
early warning systems, forecasting and evacuation plans; and
improved solid waste management systems.
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Make Land-use Planning an Instrument for Risk
Reduction:
German Flood Control Act 2005
Guiding principle
More space for rivers
Corresponding Legislation
Flood protection defined as issue
of spatial planning
Retain floods in remote States are obliged to designate
areas
more areas as flood plains
Control urban
development– reduce
damage potential
Planning new housing areas in
flood plains is for the first time
prohibited by law
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Case Study: The LifE Project – Making Space
for Water
The LifE project adopted a non-defensive approach to flood risk
management, which marked a shift from traditional thinking by permitting
water into sites in a controlled manner to make space for water.
Principles:
•
•
Living with Water: Adapting to
increased flood frequency and severity,
likely to happen with climate change
Making Space for Water: Working with
natural processes to provide room for the
river and sea to expand in times of flood
and reduce reliance on defenses, where
possible.
Zero Carbon: Providing all energy
needs from renewable resources on site,
such as wind, tidal and solar power.
Baca Architects
•
Policy lessons:
•
•
•
Flood risk management
Renewable energy
Development and amenity
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Case Study: Integrated Flood Management
Strategy for Ho Chi Minh City, Vietnam
Components:
• Protection to an appropriate return frequency,
determined by predictions using historical data
and non-stationary analysis
• Adaptation to cope with extreme events that
surpasses design criteria
• Retreat, which means restoring space for
water to adapt to long-term climate changes.
Policy lessons
• Urban flood risk management cannot be
associated solely with hard-engineered
measures, but rather with an integrated and
flexible approach in order to respond to future
climate and socio-economic uncertainties.
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Ho Long Phi
Urban growth in the periphery of the city had as a result newly-urbanized districts arising in
sites at flood risk. Hard engineering or structural measures to minimize flood risk might be
unsustainable under large hydrological, land subsidence and urbanization uncertainties.
According to the Steering Center for Urban Flood Control in HCMC an integrated flood
management strategy (IFMS) is most likely to be successful in reducing flood risk.
Prepare for the Unexpected!
“The basic issue is finding ways to build
into near-term investments and choices
an appropriate consideration of longterm trends and worst-case scenarios.”
-Andrew Revkin
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Questions for Discussion
• Have you ever experienced floods?
• If so, what types of flooding were these and what caused
them?
• Do you live in an urban center / area frequently exposed to
flooding?
• How do you prepare for a flood event?
• What do you think would be the main challenge to
improving flood resilience of your city/area?
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Thank you!
Abhas K. Jha
ajha(at)worldbank.org
Practice Leader,
Disaster Risk Management
East Asia and the Pacific
The World Bank
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