UK Climate Projections: impacts on appraisal of flood schemes

Continuing with our collection of UK Climate Projections 2018 (UKCP18) blogs, below we consider the impact of UKCP18 data and outputs on the appraisal of flood schemes.

Climate change inputs in terms of increasing river flows, sea level rise and precipitation changes are of critical importance to assessing, designing and reviewing flood mitigation schemes. The need to assess climate impacts are now critically important, particularly for appraisers collaboratively working with the Environment Agency and other flood authorities that need to assess future climate impacts throughout the lifetime of a flood scheme.

Current guidance requires appraisers to consider the timing and scale of climate changes throughout the appraisal period as well as at the end where outcome measures are defined. Much of the current guidance stipulated by flood authorities in the UK originates from derived products based on the UKCP09 datasets.

Opportunities to incorporate UKCP18 data

Whilst the need for these derived products and guidance will not change (estimated ‘uplift’ figures for flood flows within catchments will still be needed post UKCP18), there may be opportunities to incorporate some of the UKCP18 data directly into current scheme designs or to validate existing schemes against this latest data.

For example, the sea level rise data produced by UKCP18 will provide appraisers with updated sea level rise estimates for the UK coastline for any year of interest. Whilst UK flood authorities may not recommend direct usage of this data in this funding cycle, or until further analysis or review of the information has been carried out (and further guidance and recommendations will be made to ensure consistency across their work), there may be opportunities to validate proposed designs now.

Finer model resolution

Furthermore, the ‘uplifts’ used for rainfall amounts for surface water flood risks were previously based on the outputs of relatively coarse-scale climate models. A core uncertainty in these outputs was the rainfall intensity over short durations and how this might change under climate scenarios.

UKCP18 climate models use a much finer model resolution to resolve the hydrometric processes that cause high-intensity rainfall in the UK. It is hoped that the outputs from these models will give appraisers more spatially refined estimates of how high-intensity rainfall will change over time.

For more information on high intensity rainfall uplifts, see our previous UKCP18 blog.

It is highly likely that further research derived products and guidance will be necessary to provide appraisers with a suitable set of ‘uplift’ recommendations to be used across the UK, providing the necessary consistency that flood authorities require. However, it is hoped that a more spatially and temporarily refined set of figures will be given.

Whatever the outputs, the next few years are likely to be full of updates and guidance revisions that all practitioners will need to be aware of. Watch this space!

Want to know more?

Email Angus Pettit for more information on the impacts on the appraisal of flood schemes. You can also find out more about our work in this area on our climate resilience web page.

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