Demographic and climate Demographic and climate change influences on change influences on

future pluvial flood riskfuture pluvial flood risk

Donald HoustonDonald Houston11

Alan WerrittyAlan Werritty22

11Centre for Housing ResearchCentre for Housing ResearchUniversity of St AndrewsUniversity of St Andrews

Donald.Houston@st-andrews.ac.uk

22School of Environmental SciencesSchool of Environmental SciencesUniversity of DundeeUniversity of Dundee

a.werritty@dundee.ac.uk

IntroductionIntroduction

• What is pluvial flooding?What is pluvial flooding?

• Appraisal of current pluvial flood risk difficultAppraisal of current pluvial flood risk difficult

• Appraisal of future risk even more difficult!!Appraisal of future risk even more difficult!!

• Hydrological and climate change influencesHydrological and climate change influences

• Demographic and social influencesDemographic and social influences

The determinants of flood riskThe determinants of flood risk(based on McLaughlin, 2011)(based on McLaughlin, 2011)

Appraisal of Current flood Appraisal of Current flood riskrisk

1.1. Where is the Where is the hazardhazard??

2.2. Where is the Where is the exposureexposure??

3.3. What receptors are most What receptors are most vulnerablevulnerable??

Most effort has gone into 1 & 2Most effort has gone into 1 & 2

Appraisal of Future flood Appraisal of Future flood riskrisk

1.1. ChangeChange in in hazardhazard

2.2. Change Change in in exposureexposure

3.3. ChangeChange in in vulnerabilityvulnerability of of receptorsreceptors

Most effort has gone into 1Most effort has gone into 1

Current flood risk (SEPA, Current flood risk (SEPA, 2011)2011)• Hazard + Exposure =Hazard + Exposure =

– 133k properties at flood risk (5%)133k properties at flood risk (5%)• Fluvial: 64%Fluvial: 64%

• Coastal: 23%Coastal: 23%

• Pluvial: 13% Pluvial: 13% (but probably a lot higher)(but probably a lot higher)

• UNCERTAINTY in extent of pluvial hazardUNCERTAINTY in extent of pluvial hazard

• What about population?What about population?

• What about vulnerability?What about vulnerability?

Vulnerability and Vulnerability and currentcurrent exposureexposure(Walker et al 2006; Werritty et al 2007; Houston et al (Walker et al 2006; Werritty et al 2007; Houston et al 2011)2011)• RiverRiver flooding: flooding:

– Socially deprived groups slightly under-Socially deprived groups slightly under-representedrepresented

• CoastalCoastal flooding: flooding:– Socially deprived groups over-representedSocially deprived groups over-represented

• SurfaceSurface water flooding: water flooding:– Socially deprived groups slightly over-representedSocially deprived groups slightly over-represented

• UNCERTAINTY: Social deprivation is a UNCERTAINTY: Social deprivation is a crude proxy for flood vulnerabilitycrude proxy for flood vulnerability

Future pluvial flood riskFuture pluvial flood risk

• Change in Change in hazardhazard– UK uplift in extreme UK uplift in extreme dailydaily rainfall: 8% rainfall: 8%– UK uplift in extreme UK uplift in extreme hourlyhourly rainfall: ??? rainfall: ???

• Change in Change in exposureexposure::– UK population growth 1990-2050: 48%UK population growth 1990-2050: 48%– 1.2 million additional people at pluvial flood 1.2 million additional people at pluvial flood

risk (Houston et al 2011):risk (Houston et al 2011):• Climate change: 300kClimate change: 300k

• Population growth: 900kPopulation growth: 900k

• Change in Change in vulnerabilityvulnerability: ???: ???

Increase in pluvial flood riskIncrease in pluvial flood risk

Level of certainty in pluvial Level of certainty in pluvial flood risk appraisalflood risk appraisal(Low, Moderate, High)(Low, Moderate, High)

Current Future

Hazard Moderate Moderate

Exposure Moderate Low

Vulnerability Moderate Low

Vulnerability and Vulnerability and futurefuture risk risk

• Population ageingPopulation ageing

• Insurance withdrawal/higher premiums?Insurance withdrawal/higher premiums?

• Flood risk areas blighted?Flood risk areas blighted?

• Developed for social housing?Developed for social housing?

ConclusionsConclusions

• More emphasis in flood risk appraisal More emphasis in flood risk appraisal required on:required on:– PopulationPopulation– Population growthPopulation growth– Demographic changeDemographic change

• More research required onMore research required on– Extreme rainfall under climate changeExtreme rainfall under climate change– Surface water flooding modellingSurface water flooding modelling– Population change in flood risk areasPopulation change in flood risk areas– Social vulnerability to floodingSocial vulnerability to flooding

ReferencesReferences

• Houston, D., Werritty, A., Bassett, D., Geddes, A., Houston, D., Werritty, A., Bassett, D., Geddes, A., Hoolachan, A. and Macmillan, M. (2011) Hoolachan, A. and Macmillan, M. (2011) The The Invisible Hazard: pluvial flood risk in urban areas. Invisible Hazard: pluvial flood risk in urban areas. York, Joseph Rowntree Foundation. (Due for York, Joseph Rowntree Foundation. (Due for publication summer 2011).publication summer 2011).

• Walker G, Burningham K, Fielding J, and Smith G Walker G, Burningham K, Fielding J, and Smith G (2006) (2006) Addressing Environmental Inequalities: Addressing Environmental Inequalities: Flood Risk. Flood Risk. R&D Technical Report, SC020061/SR1, R&D Technical Report, SC020061/SR1, Bristol, Environment Agency. Bristol, Environment Agency.

• McLaughlin, M. (2011) McLaughlin, M. (2011) Nation Flood Risk Nation Flood Risk Assessment.Assessment. Presentation to SNIFFER Flood Risk Presentation to SNIFFER Flood Risk Management Conference, Edinburgh, March Management Conference, Edinburgh, March 2011.2011.