CCC Flood Review Report – Sayers https://www.ukclimaterisk.org/wp-content/uploads/2020/07/Future-Flooding-Main-Report-Sayers-1.pdf

Third UK Climate Change Risk Assessment (CCRA3) Future flood risk Main Report

Sayers, P.B, Horritt, M.S, Carr, S, Kay, A, Mauz, J, Lamb, R and Penning-Rowsell, E

Summary

‘Background Under the Climate Change Act 2008 the UK Government is required to publish a Climate Change Risk Assessment (CCRA) every five years. Following publication of the first two assessments (2012, 2017) the third is due in 2022 and will feed into the development of the next National Adaptation Programme (NAP) for England due in 2023, as well as the National Adaptation Programmes of Scotland, Wales and Northern Ireland. Each of these previous assessments include supporting research into future flood risks. This report builds upon those previous assessments to provide an updated (highly spatially resolved and disaggregated) assessment of current and future flood risks.

Approach The Future Flood Explorer (FFE) is used to provide an estimate of future flood risk across the UK using the latest UKCP18 climate projections. The updated analysis (an evolution of the model used in CCRA2, Sayers et al., 2015) provides a credible emulation of the UK flood risk system and its response to future change (climate change, population growth and adaptation) within a highly efficient computational framework. This enables multiple future scenarios to be explored. Here this includes two future epochs (2050s and 2080s); two climate futures (a 2C and 4C rise in Global Mean Surface Temperature (GMST) by 2100 relative to pre-industrial times); and two population projections (low and high).

These are combined with three alternative adaptation portfolios representing: (i) a continuation of Current Levels of Adaptation (CLA), assuming current policies continue to be implemented; (ii) an Enhanced Whole System (EWS) adaptation approach, assuming more ambition adaptation is implemented, and (iii) a Reduced Whole System (RWS) approach, assuming a less ambition adaptation. Key messages

How might flood risk change in the future if we continue to manage flood risk as at present?

Assuming a continuation of Current Levels of Adaptation, Expected Annual Damages (EAD, including direct economic damage to residential and non-residential properties and associated indirect damages) are set to increase from present-day levels. Under a 2C future EAD rises from £2bn today to between £2.7-3.0bn in the 2080s (depending upon associated population growth). Under a 4C future risks rise to between £3.5-3.9bn.

What is the relative importance of different flood hazards on future flood risk?

Fluvial flood risk is dominant today when looking at the UK as a whole, and remains so in the future; rising from an EAD of ~£1.1bn today to between ~£1.2bn (2C low population growth) and ~£1.6bn 4o C high population growth) by the 2080s assuming a continuation of Current Levels of Adaptation. The increase in fluvial flood risk is, however, proportionally less than for either coastal or surface water flooding. Surface water and coastal risks more than double under a 4C high population growth future (surface water risks rising from ~£0.6bn to ~£1.2bn by the 2080s and coastal risks increasing from ~£0.4bn to ~£1.0bn). Groundwater flooding remains a small proportion of the UK risk (rising from £54m to £95m).

What is the relative influence of climate change, population, and adaptation on future flood risk?

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