Demographic and climate change influences on future pluvial flood risk Donald Houston 1 Alan Werritty 2 1 Centre for Housing Research University of St Andrews 2 School of Environmental Sciences University of Dundee

Introduction What is pluvial flooding? What is pluvial flooding? Appraisal of current pluvial flood risk difficult Appraisal of current pluvial flood risk difficult Appraisal of future risk even more difficult!! Appraisal of future risk even more difficult!! Hydrological and climate change influences Hydrological and climate change influences Demographic and social influences Demographic and social influences

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

Appraisal of Current flood risk 1. Where is the hazard? 2. Where is the exposure? 3. What receptors are most vulnerable?  Most effort has gone into 1 & 2

Appraisal of Future flood risk 1. Change in hazard 2. Change in exposure 3. Change in vulnerability of receptors  Most effort has gone into 1

Current flood risk (SEPA, 2011) Hazard + Exposure = Hazard + Exposure = –133k properties at flood risk (5%) Fluvial: 64% Fluvial: 64% Coastal: 23% Coastal: 23% Pluvial: 13% (but probably a lot higher) Pluvial: 13% (but probably a lot higher) UNCERTAINTY in extent of pluvial hazard UNCERTAINTY in extent of pluvial hazard What about population? What about population? What about vulnerability? What about vulnerability?

Vulnerability and current exposure (Walker et al 2006; Werritty et al 2007; Houston et al 2011) River flooding: River flooding: –Socially deprived groups slightly under-represented Coastal flooding: Coastal flooding: –Socially deprived groups over-represented Surface water flooding: Surface water flooding: –Socially deprived groups slightly over-represented UNCERTAINTY: Social deprivation is a crude proxy for flood vulnerability UNCERTAINTY: Social deprivation is a crude proxy for flood vulnerability

Future pluvial flood risk Change in hazard Change in hazard –UK uplift in extreme daily rainfall: 8% –UK uplift in extreme hourly rainfall: ??? Change in exposure: Change in exposure: –UK population growth : 48% –1.2 million additional people at pluvial flood risk (Houston et al 2011): Climate change: 300k Climate change: 300k Population growth: 900k Population growth: 900k Change in vulnerability: ??? Change in vulnerability: ???

Increase in pluvial flood risk

Level of certainty in pluvial flood risk appraisal (Low, Moderate, High) CurrentFuture HazardModerate ExposureModerateLow VulnerabilityModerateLow

Vulnerability and future risk Population ageing Population 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?

Conclusions More emphasis in flood risk appraisal required on: More emphasis in flood risk appraisal required on: –Population –Population growth –Demographic change More research required on More research required on –Extreme rainfall under climate change –Surface water flooding modelling –Population change in flood risk areas –Social vulnerability to flooding

References Houston, D., Werritty, A., Bassett, D., Geddes, A., Hoolachan, A. and Macmillan, M. (2011) The Invisible Hazard: pluvial flood risk in urban areas. York, Joseph Rowntree Foundation. (Due for publication summer 2011). Houston, D., Werritty, A., Bassett, D., Geddes, A., Hoolachan, A. and Macmillan, M. (2011) The Invisible Hazard: pluvial flood risk in urban areas. York, Joseph Rowntree Foundation. (Due for publication summer 2011). Walker G, Burningham K, Fielding J, and Smith G (2006) Addressing Environmental Inequalities: Flood Risk. R&D Technical Report, SC020061/SR1, Bristol, Environment Agency. Walker G, Burningham K, Fielding J, and Smith G (2006) Addressing Environmental Inequalities: Flood Risk. R&D Technical Report, SC020061/SR1, Bristol, Environment Agency. McLaughlin, M. (2011) Nation Flood Risk Assessment. Presentation to SNIFFER Flood Risk Management Conference, Edinburgh, March McLaughlin, M. (2011) Nation Flood Risk Assessment. Presentation to SNIFFER Flood Risk Management Conference, Edinburgh, March 2011.