Risk/opportunity:(from the Climate Change Risk Assessment for Scotland 2012):
BE10, BE11, BE12, BE15, BE18, FL6, FL24 Property at significant risk of flooding
Narratives: Flooding and infrastructure, Climate change risks to society and our capacity to adapt
SCCAP theme: Buildings and infrastructure Society
SCCAP objectives:
B2: Provide the knowledge, skills and tools to manage climate change impacts on buildings and infrastructure
S1: Understand the effects of climate change and their impacts on people, homes and communities
S2: Increase the awareness of the impacts of climate change to enable people to adapt to future extreme weather events
S3: Support our health services and emergency responders to enable them to respond effectively to the increased pressures associated with a changing climate
|
Figures are from SEPA’s FRM Strategy Characterisation Data (2015). Number of properties affected given to 2 significant figures. |
- Flooding is already a widespread issue in Scotland, causing significant economic and social damage. Climate change is projected to increase flood risk
- Flooding can originate from pluvial (rain), fluvial (river) or coastal waters. The risk from each of these is modelled separately by SEPA
- Met Office records show that precipitation increased by an average of 27% across Scotland between 1961 and 2011. This trend is projected to continue due to climate change.
- The increase in winter precipitation intensity and frequency will increase flood risk, as will the projected increases in coastal storm surges
- Using modelled flood risk can help ensure that planning decisions take account of future risk, and that flood protection schemes receive appropriate levels of resource
Flooding is already a significant and widespread issue in Scotland. Floods cause major economic losses and associated disruption and misery to those affected by them. The social disruption caused by floods can seriously undermine the quality of life of individuals and impact on the fabric of affected communities (Gordon, 2004).
Estimates of the cost of annual flood damage to property in Scotland lie at around £210 million (Scottish Government, 2014, JBA Technical report) to £250 million (SEPA, 2015). Individual flooding events can have a huge cost - losses of £30 million were estimated for the Tay/Earn flood in 1993 and £100 million for the Strathclyde flood in 1994 (Scottish Executive, 2002).
Climate change is projected to increase existing flood risk and flood damage. Annual rainfall levels in Scotland have already increased 27% between 1961 and 2011, and average winter rainfall has increased even more – at over 45% on average, with this rising to over 50% in the north of Scotland (Sniffer, 2014).
Days of heavy rainfall (defined as over 10mm within 24 hours) have also increased, particularly in the north and west of Scotland, which show an average increase of 8 days between 1960 and 2011. Likewise, the maximum rainfall recorded over any five day period in a year has also increased - on average by 20% across Scotland.
If such rainfall trends continue they will increase the frequency, severity and extent of flood events. The realised impact of flood events depends on factors including the number and location of properties, infrastructure and communities in flood risk areas. This indicator highlights the underlying risk and so can help inform decisions about adaptive actions ranging from flood avoidance through planning, minimising flood damage through preparation, investing in flood defences and strategic relocation.
Related Indicators:
BB11 Planning Decisions that do not reflect SEPA’s flood risk advice
Figures for the numbers of property identified as at risk from flooding are shown below in Table 1. The table covers three levels of flooding between high and medium risk (from any flood source)
Table 1 Risk to Property from flood events.
|
Likelihood of Flood Occurrence |
No. of Property type affected |
||
|
Residential |
Non-residential |
All Property |
|
|
1 in 10 year flood (high risk) |
21,000 |
9,900 |
31,000 |
|
1 in 200 year flood (medium risk) |
79,000 |
29,000 |
110,000 |
|
Likelihood of Flood Occurrence |
Percentage of Property type affected |
||
|
Residential |
Non-residential |
All Property |
|
|
1 in 10 year flood (high risk) |
0.8% |
2.9% |
1.1% |
|
1 in 200 year flood (medium risk) |
3.2% |
8.6% |
3.8% |
Figures are from SEPA’s FRM Strategy Characterisation Data (2015). Number of properties affected given to 2 significant figures.
Less than 1% of residential property is at risk of a high probability flood even (a ‘1 in 10 year’ event), but 3.2% are at risk from a medium likelihood event (a 1 in 200 year event). Non-residential property is at greater risk than dwellings.
Sources of Flood Risk
The number and percent of properties affected by each flood source are shown below in Table 2. The greatest cause of flood risk to residential property comes from fluvial flooding, which contributes over 50% of the flood risk for this group. Non-residential property is at roughly equal risk from fluvial and surface water flooding, each of these contributing around 40% of the total risk to this group.
Table 2 Numbers of Properties at risk from each flood source
|
Flood Source |
Surface Water |
Fluvial |
Coastal |
|||
|
Annual Probability of Flood |
10% High |
0.5% Med |
10% High |
0.5% Med |
10% High |
0.5% Med |
|
Residential |
5,600 |
28,000 |
13,000 |
49,0000 |
4,200 |
11,000 |
|
% of total residential at risk |
0.2 |
1.1 |
0.5 |
2.0 |
0.2 |
0.4 |
|
Non-Residential |
4,600 |
16,000 |
4,7000 |
13,000 |
1,600 |
4,400 |
|
% of total non-residential at risk |
1.4 |
4.7 |
1.4 |
3.9 |
0.5 |
1.3 |
Figures based on SEPA’s FRM Strategy Characterisation Data (2015). Number of properties affected given to 2 significant figures.
Legislation and Management of Flood Risk
Scottish flood risk legislation and management was comprehensively updated with the Flood Risk Management (Scotland) Act 2009 (FRM Act). Under this Act, the primary responsibility for protecting land from flooding continues to lie with land and property owners. Notwithstanding, Scottish Government provides some funds to local authorities for flood protection schemes. For example, in 2014 they increased funding for flood defences, allocating an additional £40 million[1].
The roles and responsibilities of various public bodies to help manage and reduce flood risk are set out in the FRM Act[2]. These bodies include SEPA, Local Authorities, Scottish Water, Forestry Commission Scotland, National Parks Authorities and Scottish Government.
The FRM Act introduced a new approach to flood management in Scotland by considering whole catchments and all types of flooding, and introduced a requirement for sustainable flood management. The Act has introduced a coordinated process to manage flood risk at a national and local level. Specific measures within the Act include:
- A framework for coordination and cooperation between all organisations involved in flood risk management
- Assessment of flood risk and preparation of flood risk management plans
- New responsibilities for SEPA, Scottish Water and local authorities in relation to flood risk
- A revised, streamlined process for flood protection schemes
- Methods to enable stakeholders and the public to contribute to managing flood risk
- A single enforcement authority for the operation of Scotland's reservoirs (SEPA)
Flood Risk Management Strategies (FRM Strategies) coordinate efforts to tackle flooding in Scotland. They set out a national approach to flood risk management and help coordinate action and investment across public bodies. FRM Strategies for each of Scotland’s 14 Local Plan Districts (LPDs) were published in December 2015 (SEPA, 2015).
In addition, Local Flood Risk Management Plans (FRM Plans) will provide local detail on the funding and delivery timetable for actions between 2016-2021. The publication date for Local Flood Risk Management Plans is June 2016. Local Flood Risk Management Plans and Flood Risk Management Strategies will be updated every six years (ibid).
Fluvial and Surface Water Flooding: Trends in Precipitation
Precipitation is the primary driver for flooding. Data collected by the Met Office for the UK’s Climate Projections 2009 (UKCP09; data from 1914 – 2011) shows clear trends (of 95% statistical confidence) in increased precipitation in the following ways (SNIFFER, 2014):
- Total annual precipitation has increased on average by 27% across Scotland since 1961, with most of the increase falling in winter.
- In each region, and across the country, the change in winter precipitation since 1961 shows a clear upward trend (with a 45% average increase). No clear trends in average summer rainfall have been noted
- Since 1961 there has also been a trend of increasing ‘heavy rainfall days’ in winter (where ‘heavy rain’ is defined as over 10mm in 24 hours). In particular, North and West Scotland have seen increases of more than seven and eleven days respectively.
- The maximum precipitation recorded within any five day period in a year has also increased across Scotland. The average increase since 1961 is over 20%.
As well as precipitation, other factors such as the extent of impermeable surfaces will also affect flood extent and severity. Based on precipitation data alone, one would expect the risk of flooding to have increased since 1960.
Fluvial Flooding since 1950
River flow records show high variability in both the frequency and severity of floods since the 1950s. Whilst the 1980s and 90s were exceptional for many rivers, the frequency of flooding was higher in the 1950s, especially in the north. However, since 1989 more than half of Scotland’s largest rivers (8 out of 16, and notably those draining from the west) have recorded their highest flows (reflecting vigorous westerly storms prevalent during the late 1980s and 1990s). This ‘flood rich’ period suggests that the probability of experiencing a fluvial flood has substantially increased.
Coastal Flooding
Coastal flooding is exacerbated by sea level rises and by storm surges during high or spring tides. Global sea levels have risen over the last century by 1-2 mm per annum - the observed global mean sea level rise during the period 1961–2003 is 1.8 mm yr (IPCC, 2007). However, the change in relative sea level varies as different parts of Scotland are uplifting at different rates after de-glaciation. In Scotland the Aberdeen tidal gauge (dating back to 1862) records an average sea level rise of 0.69mm per year (Scottish Executive, 2002).
Scotland has relatively tight controls on planning to ensure that future developments are not sited in areas at risk (see Indicator BE11). Nonetheless, projected increases in precipitation will undoubtedly increase the number of properties at flood risk.
A study conducted for Scottish Government by JBA Consulting has examined the increase in flood risk to all property by 2035 in some detail. Some of their findings are shown in the Table 3 below (Pettit et al, 2014b). The figures allow for the expected increase in property numbers as well as a modelled increase in the extent and frequency of flood events. Note that their figures were derived using an early version of SEPA’s flood hazard modelling, and a slightly different approach to estimating flood risk, thus there are differences between the two sets of estimates. Their methodologies are given in full in their report. In addition, the JBA study was based on data provided by SEPA before it was fully finalised. Nonetheless, their study provides useful insight into the likely upward trends for flood risk and their analysis indicates significant increases in both the percentage of and the numbers of properties affected by flooding.
One important aspect is that these projections show that “with relatively small increases in sea level, (river) flow and rainfall, the number of properties at risk of flooding could increase substantially, particularly for the more frequent flood events.” (i.e. those events likely to occur once every 10 years) (JBA, Sept 2014). If this prediction is backed up by further research, this could have implications for flood risk management in Scotland, which may need to increase the emphasis on dealing with more frequent lower return period floods.
Table 3 Flood Risk to Property - Predicted Changes (note that ‘AP’ stands for Annual Probability). (Pettit et al, 2014b)
|
Fluvial |
10% AP 10yr |
3.33% AP 30yr |
2% AP 50yr |
1% AP 100yr |
0.5% AP 200yr |
0.1% AP 1000yr |
|
Current estimates |
15,420 |
29,775 |
33,974 |
39,030 |
49,657 |
76,341 |
|
2035 estimates |
18,456 |
35,731 |
40,892 |
46,910 |
59,985 |
94,801 |
|
Increase |
3,036 |
5,956 |
6,918 |
7,880 |
10,328 |
18,460 |
|
% increase |
19.7% |
20.0% |
20.4% |
20.2% |
20.8% |
24.2% |
|
Coastal |
10% AP 10yr |
4% AP 30yr |
2% AP 50yr |
1% AP 100yr |
0.5% AP 200yr |
0.1% AP 1000yr |
|
Current estimates |
4,121 |
6,132 |
7,258 |
9,380 |
11,192 |
17,438 |
|
2035 estimates |
6,107 |
7,677 |
9,770 |
11,958 |
15,402 |
18,698 |
|
Increase |
1,986 |
1,545 |
2,512 |
2,578 |
4,210 |
1,260 |
|
% increase |
48.2% |
25.2% |
34.6% |
27.5% |
37.6% |
7.2% |
|
Surface Water |
10% AP 10yr |
3.33% AP 30yr |
2% AP 50yr |
1% AP 100yr |
0.5% AP 200yr |
|
Current estimates |
9,672 |
15,093 |
18,882 |
24,438 |
31,491 |
|
2035 estimates |
12,052 |
18,021 |
21,811 |
28,153 |
33,348 |
|
Increase |
2,380 |
2,928 |
2,929 |
3,715 |
1,857 |
|
% increase |
24.6% |
19.4% |
15.5% |
15.2% |
5.9% |
Coastal flooding will be exacerbated by sea level rises and storm surges. The range of absolute sea level rise for the UK (i.e. before land movements are included) is projected to be between 12 and 76 cm for 1990–2095 (Medium emissions scenario).[1] This will be accompanied by a small increase in the ‘storminess-driven’ component of extreme sea level, predicted to be under 0.9 mm yr.[2]
[2] See UK Climate Projections science report: Marine & Coastal, Chapter 4. Also http://ukclimateprojections.metoffice.gov.uk/22569
It is possible to identify the areas of least and greatest change between the current risk and the risk projected for 2035 (Pettit et al, 2014b). The following figures all refer to flood events of an annual probability (at present) of 0.5%.
The increase in property numbers at risk from surface water flooding is fairly even across Scotland, with an average increase of 5.9%, which represents around 1800 additional properties at risk.
Coastal flooding will affect over 4000 additional properties, with the increase concentrated in certain areas, for example in Aberdeenshire (50% increase in property at risk) and in Dundee City (250% increase), each of which will have over 280 additional properties at risk by 2035.
Over 10,000 additional properties that will be at risk of fluvial flooding in 2035. Table 4 below shows a few of the areas with the least and greatest increase in numbers at risk.
Table 4 Example areas with least and greatest increases in property at risk of Fluvial Flooding
|
Local Authority Area |
% Increase |
Additional dwellings at risk |
|
Minor Increase (<5%) |
||
|
Aberdeen |
2.61 |
123 |
|
Moray |
3.42 |
81 |
|
Major increase (>20% or > 1000 additional properties at risk) |
||
|
Highland |
23.53 |
1048 |
|
Stirling |
51.88 |
1049 |
|
Falkirk |
91.65 |
911 |
Source: (Pettit et al. 2014b).
No measured trend is available as yet. However, the predicted trend is upward, reflecting both an increase in the extent and severity of flood events as well as a modest increase in the number of properties at risk in Scotland (though flood risk assessment during the planning processes ensures that very few developments are created in flood risk areas – see associated indicator BB11).
If there are any future changes to either the input data or the flood risk modelling currently used by SEPA this will make tracking flood risk trends more difficult. For example, coastal modelling doesn’t currently include wave overtopping.
Pettit, A., May, P., Bassett, D. (2014). Assessing the Flood Risk Management Benefits of Property Level Protection - Evidence Summary. Edinburgh: Scottish Government. Available at http://www.gov.scot/Topics/Environment/Water/Flooding/resources/research
Pettit, A., May, P., Bassett, D. (2014). Assessing the Flood Risk Management Benefits of Property Level Protection - Technical and Economic Appraisal Report. Edinburgh: Scottish Government. Available at http://www.gov.scot/Topics/Environment/Water/Flooding/resources/research
Scottish Government (2007) Exploring the Social Impacts of Flood Risk and Flooding in Scotland http://www.scotland.gov.uk/Publications/2007/04/02121350/5
Scottish Executive (2002) Climate Change: Flooding Occurrences Review http://www.scotland.gov.uk/Publications/2002/03/10817/File-1
SEPA (2015) Flood Risk Management Strategy Characterisation Data
SEPA (2016) Flood Risk Management Strategies. Available at http://apps.sepa.org.uk/FRMStrategies/
Sniffer (2014) Scotland’s Climate Trends Handbook, Sniffer Project CC13, available online at http://www.environment.scotland.gov.uk/climate_trends_handbook
General Register Office for Scotland (Households and dwellings) http://www.nrscotland.gov.uk/statistics-and-data/statistics
SEPA (2011). National Flood Risk Assessment (NFRA) http://www.sepa.org.uk/flooding/flood_risk_management/national_flood_risk_assessment.aspx
SEPA (2016) Flood Risk Management Strategies http://apps.sepa.org.uk/FRMStrategies/
Black, A, Burns JC. (2002) Re-assessing the flood risk in Scotland. http://www.ncbi.nlm.nih.gov/pubmed/12169005
Pettit, A., May, P., Bassett, D. (2014). Assessing the Flood Risk Management Benefits of Property Level Protection - Blueprint for Local Authorities and Scottish Water. Edinburgh: Scottish Government. Available at http://www.gov.scot/Topics/Environment/Water/Flooding/resources/research
Lead author: Katherine Beckmann (Heriot-Watt University).
Angus Pettit, Principal Analyst at JBA Consulting, and the main author of the JBA reports.
Mark McLaughlin and David Faichney of SEPA.
Anne Marte Bergseng
