assessing the benefits of flood warning: a scoping study sniffer ukcc10 bridget woods ballard, hr...

Assessing the benefits of flood warning: a scoping study

SNIFFER UKCC10

Bridget Woods Ballard, HR Wallingford

SNIFFER UKCC10


Introduction

© HR Wallingford 2005 April 18, 2023

Project Team


(Project Managers/DSS)

John Chatterton, JC Associates

(Tangible benefits)

Maureen Fordham, Northumbria University (Intangible benefits, pilot studies)


Project objectives: Phase 1

• To review current practice in the assessment of the benefits of flood warning in the UK and internationally;

• To characterise the extent and type of benefits assessed;

• To identify key characteristics of different approaches;

• To consider the appropriateness of the methods for assessments in Scotland;

• To develop a preliminary method for pilot testing.


Flood warning objectives

The main purpose of flood warning is to save life by allowing people, support and emergency services time to prepare for flooding.

The secondary purpose is to reduce the effects and damage of flooding.

(Defra, 2004)


Economic costs of flooding

• Strathclyde, 1994: £100 million• Tay/Earn, 1993: £30 million• August 2002: £7.2 - £31 million• Average annual damage across Scotland:

£185 million (inland) and £59 million (coastal) – assuming no effective standard of protection

• Average annual damage across Northern Ireland: £100 million – assuming current protection levels

• Climate change – increased depth and frequency of flooding ?


Benefits of flood warning

The reduction in losses (tangible and intangible) resulting from the provision of a warning when compared to the situation prior to the operation of the warning system.


Tangible losses

Cost of damage arising as a consequence of the physical contact of floodwater with infrastructure (direct losses), and the losses which are consequent upon direct flood damage (indirect losses)Flood warning systems can provide a reduction in direct losses through:

− timely operation of flood control structures− pre-event maintenance operations to ensure free channel

conveyance− installation of local resilience measures− removal of property (including livestock) from flood risk

area


Intangible losses

• Loss of life and injury;• Damage to human health and long-term well-

being.

Flood warning systems can provide a reduction in intangible losses through:

− facilitating timely evacuation;− promoting a sense of security;− raising awareness of floods and supporting individual

and community action.


Drivers for a new benefit assessment tool

• Deficiencies in current method identified by FHRC

• Civil Contingencies Act, 2004• Requests for new schemes• Ongoing R&D by SE on FW communication

methods and social impacts of flooding• SEPA’s 2nd generation flood maps, national

flood mapping for Northern Ireland


Literature Review - general

• Paucity of data on benefits of flood warnings• Evidence of increased risk to life when focus is

on saving stock/property• Importance of intangibles – but no models

proposed• Geography, hydrology/hydraulics, social

demography all play key and complex roles in determining characteristics of response and level of benefit

Assessment of Tangible Benefits


Literature review – focus (tangibles)

• Provenance and quality of base data• Potential savings assuming perfect institutional

and individual response• Effectiveness of response in translating

potential to actual savings• Uncertainties


Key tangible methodologies

• Parker, 1991: % flood damage reduction resulting from flood warnings (varying with flood depth, property type)

• Factors used to adjust PFA, according to reliability, availability, ability, activity (subsequently subject to scrutiny)

• 1995, method automated through spreadsheet analysis to allow calculation of opportunity benefits of improving reliability and lead times – however model audits of base data difficult


Latest R&D

• Defra, 2005: Multi-Coloured Manual ‘The Benefits of Flood and Coastal Risk Management: A Manual of Assessment Techniques’

• FHRC: Objective 13 – the damage reducing effects of flood warnings: results from new data collection


Conclusions• Current flood warning services might contribute

to saving only 5% of the total potential damages• The incremental savings of warned vs not

warned was < £1,000 per household• Those less able did not appear to save less than

those fully able• Flood depth and duration did not appear to affect

amount saved• Effective response does not mean 100%

potential savings.


Operational benefits

• Closing gates / barriers• Installing temporary defences• Channel clearance


Resilience measures

• Need full resilience (i.e. tanking and flood water ingress point barriers) to prevent any water damage to property and minimise clean-up costs (can be significant)

• MCM 2005 suggests that £38K damage per house for flooding of 1m (inc. £10K clean-up). Flood resilience could save much of this compared to £2,000 saved from moving possessions.


Agricultural benefits

• Potentially significant contribution to benefits where stocking densities on floodplain high

• Simple trigger level systems may be sufficient for isolated farms

• ‘Islands of safety’ may be appropriate measures (with or without a flood warning system)

• Intangible farmer benefits could be significant but untested as yet


Uncertainties

• FHRC, 2006: £ value of savings/household ranged from £25 to £10,776

• Merz et al, 2004

Assessment of Intangible Benefits


Key Intangible Methodologies, 1

Green and Penning-Rowsell (1989) - “Flooding and the quantification of ‘intangibles”

• ‘Bootstrapping’ procedure - related known monetary losses (direct damages) to intangible losses by deriving equivalent values. Used extensive quantitative surveys

• Found monetary equivalents of intangible impacts far exceeded direct damages – some were double


Variability in Rating Severity of Effects of FloodingRating scale: 0-10 Table 152 + Table 16 - Relative severity of different impacts of flooding as assessed by those who reported experiencing each impact (Source: Green and Penning-Rowsell 1989: 29) and Subjective rating of severity of the effects of flooding (adapted from DEFRA/EA 2004: A4-37) respectively.

Swalecliffe Uphill DEFRA/EA 2004

Damage to house structure 5.0 5.0 6.4

Damage to replaceable contents

9.0 7.0 6.5

Loss of memorabilia/ Irreplaceable items loss

10.0 7.0 5.6

Health effects 7.5 5.0 4.5

Stress of the flood itself 10.0 n/a 7.1

Evacuation/ Having to leave home

10.0 6.0 7.0

Disruption/ Getting house back to normal

10.0 10.0 7.8



DEFRA/EA 2004 - Appraisal of Human-Related Intangible Impacts of Flooding

• £200 per household per year - identified as representing the benefits of a reduction in health impacts of flooding

• But found receipt warning made very little difference to physical or psychological impacts or short and long term mental impacts

• Didn’t focus on warning benefits



DEFRA/EA (2006) Flood Risks to People project, Phase 2

• “Timely and effective flood warnings help to reduce the risk to life and serious injury from flooding”

• “The main … function of flood warnings is to alert people to reduce property damage”

• Focus on primary intangibles – death and serious injury


Stressful Effects of Flooding Possibly Mitigated by Warning (Data adapted from Penning-Rowsell et al 2000: 11). Comment added

Stressful impacts of the flood(original 15: (a) to (o))

Comment on the extent (almost completely, partly applicable) to which an effective warning might mitigate the impact

a)Lack of warning to residents Yes, almost completely

a)Lack of advice on what to do (especially about builders, insurance)

Yes, partly. A pre-prepared leaflet/website could offer advice on how to find suitable professionals for post-flood cleanup

a)Sandbags not provided (or difficult to obtain) Yes, partly. A pre-prepared leaflet/website could offer advice on the providers of such materials

a)Relief centres not known about Yes, almost completely. This information should be included in a warning

a)No agency/authority presence during the flood Yes, almost completely. The warning is proof of agency presence at the earliest stage

a)No help from agencies with clearing houses Yes, partly. A pre-prepared leaflet/website could offer advice on how to find suitable professionals for post-flood cleanup

a)Unconvincing explanations about the causes of the flooding

Yes, almost completely. The warning should contain appropriate information such as this

a)Belief that the authorities were ‘not doing anything about the flood problem’

Yes, partly. The warning is evidence of doing something but people are usually more concerned that the risk is entirely removed

a)Belief that little or no real action has been taken on the flood warning system

Yes, almost completely

a)Unhelpful attitude of some insurance agents Yes, partly. Although this is directed at particular insurance companies/employees, information on how best to deal with such agencies could mitigate some of the negative effects


Conclusions

• Intuitively, warnings should reduce the intangible impacts of flooding

• There is only anecdotal evidence for the intangible benefits of flood warning

• Robust measurement – either quantitative or qualitative – requires some amount of new data collection

Decision Support Systems


Flood Risks to People Methodology

Ninj = Nz x Hazard Rating x Area Vulnerability x People Vulnerability

Ninj = number of injuries within a particular hazard ‘zone’Nz = number of people within the hazard zone (at ground/basement level)Flood Hazard Rating = function of flood depth/velocity (within the hazard zone being considered) and debris factorArea Vulnerability = function of effectiveness of flood warning, speed of onset of flooding and nature of area (including types of buildings)People Vulnerability = function of presence of people who are very old and/or infirm/disabled/long-term sick


Flood Risks to People Map

Recommendations


Existing SEPA approach

• Scoring, with benefit levels identified relative to ‘existing population’

Benefit Score Benefit Score Sub-Components Numbers affected Number of households

Number of special properties (e.g. hospitals, old people’s homes)

Number of businesses Area of agricultural land Level of potential

transport/communications disruption (H/M/L equates to scores of 10/5/0))

Scale of the event Average depth of water Expected duration of flood Expected speed of maximum flow

Ability to respond Warning lead time Potential for action Accuracy of prediction/modelling Perception of risk


Existing SEPA approach (cont)

• Scores of 1-10:

10 x (sub-score – dataset minimum)

(dataset maximum – dataset minimum)• Total Score per category = subscore average• Total Score (per return period))

= Nr affected x scale of event x ability to respond


Recommendations - overarching

1. Over-riding justification for flood warning should be mitigating risks to life or serious injury (primary intangible benefits)

2. Need for tangible benefit assessment to move from uni-directional (property/ possessions savings) to more holistic approach (to include benefits from operational and resilience measures)

3. Need for further research prior to inclusion of secondary intangible benefits in any economic appraisal methodology


Recommendations – overarching (cont)

4. Multi-criteria scoring approach required for strategic prioritisation of schemes nationally

5. Ground-truthing required to validate relative weights of components and influence of catchment and community characteristics on scores/weights

6. DSS to support structured, consistent decision making and to facilitate sensitivity testing. A GIS approach would allow score mapping.


Recommendations: MCA scoring

• Risks to life/serious injury• Residential property• Non-residential property• Operations: flood defence assets• Operations: watercourse capacity• Resilience• Agriculture• Social vulnerability (residential, non-residential,

agricultural)


Appropriate scores & weights

• Via focus groups and expert opinion• Pilots will also allow appropriate ‘score’

evaluating methods to be developed – either a single method, or adapted for different catchment types

• Pilot ‘economics’ will allow better understanding of likely uncertainties, costs and merits of a quantification vs ranking approach

Thank you

assessing the benefits of flood warning: a scoping study sniffer ukcc10 bridget woods ballard, hr...

Documents

hr wallingford slide

flood warning objectives

flood risk area slide

main purpose of flood

introduction slide

losses tangible

damage of flooding

national flood mapping