About the future flood maps
- Do SEPA’s Flood Maps take into account the effects of climate change?
- How do the Future flood maps account for climate change?
- Viewing the future flood maps
- What about other future changes?
- Why aren’t future flood maps available everywhere?
- What about Flood Protection Schemes?
- What about surface water flooding?
- Large differences between the two can indicate that flood hazard is more sensitive to climate change in these areas. Communities not at risk of flooding now may become at risk of flooding in the future.
- Where the area potentially at risk of flooding looks similar between the future and present day medium likelihood maps, communities may see an increase in the severity of flooding, such as higher depths of floodwater, or flood more often in the future.
- Changes in river channel or floodplain geomorphology
- Changes in land use
- Population changes
- Condition of defences or other infrastructure
- Construction of new Flood Protection Schemes, bridges or culverts.
- Coastal erosion. Coastal erosion may also increase with rising sea
levels. For more information on coastal erosion in Scotland see
Dynamic Coast: Scotland's Coastal Change Assessment. - Changes in wave overtopping or wave run-up at the coast. In many locations the size of waves at the coast is limited by the depth of water, so higher sea levels may also lead to larger waves at the coast which may lead to an additional increase in flood risk due to wave overtopping.
1. Do SEPA’s Flood Maps take into account the effects of climate change?
SEPA’s Flood Maps include two series of flood hazard maps for river and coastal flooding - ‘Present Day’ and ‘Future’ Flood Hazard maps.
Present Day flood maps – maps generated using meteorological, river flow and sea level data that are broadly representative of present day climate conditions without taking into account potential future changes due to climate change.
Future flood maps – maps generated taking into account the potential effects of climate change for a single future climate scenario based on available predictions of river flows and sea levels for the 2080s.
2. How do the Future flood maps account for climate change?
The future flood maps were developed using the same modelling and mapping approaches as the Present Day flood maps but with revisions to the peak river flow and sea levels based on projections for a single future scenario for the 2080s.
The impact of climate change on flood risk will depend on how much global action there is to reduce greenhouse gas emissions and on the characteristics of a local area. SEPA’s future flood maps currently represent one possible future, however there are uncertainties regarding emissions and climate response which mean changes in flood risk could be smaller or larger than those shown.
Emissions scenarios
Future greenhouse gas emissions depend on a range of social, economic and technological factors including, for example, population, economic growth, and energy use, as well as unknowns about how the climate system responds. For this reason climate projections are produced for a range of emissions scenarios which correspond to different ways the world might change over the rest of the 21st century.
The future flood maps have been developed using projections from a high emissions scenario where little or no action is taken to avoid dangerous levels of climate change, with greenhouse gases continuing to rise and leading to a greater global temperature increase.
Where do we get information on how climate change could affect the UK?
The UK Climate Projections (UKCP) provide assessments of how the climate of the UK may change over the 21st century.
At the time of preparation of the future flood maps, the UK Climate Projections 2009 (UKCP09) was the best available projection information for the UK and was used to inform our future flood map scenarios.
Since then, the UK Climate Projections 2018 (UKCP18) was launched and is now the most up to date information on the future climate of the UK to 2100. The future flood map climate change allowances will be reviewed in light of the new UKCP18 information, which may be incorporated into future updates.
River future flood maps
The river future flood maps reflect projected increases in peak river flows.
SEPA commissioned a study in 2011 that provided information on future changes in peak flows for Scotland’s rivers based on UKCP09 climate projections and an assessment of the vulnerability of Scotland’s river catchments to the impacts of climate change.
For each river basin region SEPA used the projected uplifts to peakflows for the High emissions scenario 67th percentile for the 2080s.
Coastal future flood maps
SEPA’s coastal flood maps reflect the risk from high tides and storm surges only. The risk associated with waves is generally not included at present.
The coastal future flood maps reflect projected increases in mean sea levels. Predicted changes in sea level vary around the coast of Scotland.
UKCP09 projections of sea level rise for the High emissions scenario 95th percentile confidence limit for the year 2080 were used and applied to uplift the sea levels from the medium likelihood (1 in 200 yr) event.
Sea level rise projections for a high emissions scenario have increased in the latest UK Climate Projections (UKCP18). Comparison with the UKCP18 projections suggests that, with limited global action to tackle climate change, there is a 1 in 2 chance that sea level rise by 2100 will be higher than that mapped in the future coastal flood maps.
Additional sea level rise beyond the current projected ranges cannot be ruled out as there is uncertainty regarding the Antarctic ice sheet contribution to sea level rise. (Fung, et al., 2018).
More information on the projections used in the future flood maps can be found on SEPA’s Developing Our Knowledge web page.
Please note, there are differences between the scenarios used within the future flood maps and the allowances in SEPA’s “Climate change allowances for flood risk assessment in land use planning guidance”. More information can be found on SEPA’s Land Use Planning pages.
3. Viewing the future flood maps
The future flood maps for river and coastal flooding can be viewed on
SEPA's Flood Maps pages.
Future and present day medium likelihood flood maps showing areas at risk of flooding can be compared by switching on both layers.
4. What about other future changes?
The future flood maps do not reflect other potential future changes which are likely to influence future flood risk, such as:
5. Why aren’t future flood maps available everywhere?
There are a small number of locations for which suitable future flood map data is not available. These locations are identified using the Future Flood Data Not Available layer. The lack of future flood map data in these locations does not mean there is no future flood risk.
As part of our ongoing flood map improvement programme, we will look to address these areas and work with our flood risk management partners to improve the flood maps.
6. What about Flood Protection Schemes?
SEPA’s Present Day river flood maps have been improved in some locations by incorporating modelling from studies for flood protection or alleviation schemes.
In some of these locations the flood study modelling has not been incorporated into the Future Flood maps and any residual benefit from flood protection schemes above their standard of protection is not shown.
Flood protection schemes are generally designed to withstand a flood of a specified likelihood or chance of occurring in any given year, sometimes referred to as the ‘design flood event’. The standard of protection that defences offer can change over time though due to a number of factors, including climate change.
7. What about surface water flooding?
Flood risk from surface water flooding is expected to increase with climate change due to projected changes in rainfall intensity.
We intend to publish a Future surface water flood map in later releases of SEPA’s flood maps. This will use new information on how climate change may affect short duration high intensity rainfall events typically responsible for surface water flooding.
The surface water present day low likelihood flood map layer, available in the Flood Map Viewer, used the medium likelihood flood event with an increase in rainfall intensity of 20% nationally. This layer may provide a first indication of those areas potentially at risk from surface water flooding in the future, however due to projected changes in rainfall intensity it may not show all locations that may be affected in the future.
References
Fung, F., Lowe, J., Mitchell, J., Murphy, J., Bernie, D., Gohar, L., . . . Sexton, D. (2018). UKCP18 Guidance: Caveats and Limitations. Exeter: Met Office Hadley Centre.
Kay, A., Crooks, S., Davies, H., & Reynard, N. (2011). An assessment of the vulnerability of Scotland's river catchments and coasts to the impacts of climate change. Wallingford: Centre for Ecology and Hydrology.