Flood disadvantage in Scotland: mapping the potential losses in well-being

2 Data and Methods

2.1 The research presented in this report is based on a quantitative geospatial assessment underpinned by the conceptual framework and literature review work reported in Lindley et al. (2011). The assessment develops and combines a series of map layers which together can be used to understand the geographical characteristics of flood disadvantage.

2.2 Table 1 summarises the data used for the work and their sources. The analysis has been carried out using the best available data at the time. Other data acknowledgements are given in Appendix 1.

Table 1 Data and data sources

2.3 The methodological basis for the production of the flood disadvantage maps, is the same as reported in Lindley et al. (2011), following the conceptual framework outlined in Chapter 1. A summary of the research stages is given in Figure 2 below. Standardised scores for neighbourhoods (Data Zone units) are combined to produce a standardised scoring scheme for the final output maps. High positive values indicate neighbourhoods with relatively high levels of socio-spatial flood vulnerability or flood disadvantage, while high negative values indicate neighbourhoods with relatively low socio-spatial flood vulnerability or flood disadvantage. Values of zero correspond to the Scottish mean. All scores have been given appropriate labels using the classification schemes outlined in Appendix 2 (Tables A2.1 and A2.2).

Figure 2 Stages in the research methodology associated with the original study (adapted from Lindley et al., 2011)

2.4 While the methods used are broadly equivalent, mapped flood disadvantage results are not directly comparable across the UK due to differences in the indicators and size of the Census units used. The Data Zone units in Scotland allow a better spatial representation of socio-spatial flood disadvantage than was used elsewhere. These units of around 750 people (500-1000) are subsequently referred to as Scottish neighbourhoods.

2.5 Two improvements to the original methodology Lindley et al. (2011) have been developed:

• Use of the percentage of residential properties as a measure of flood hazard-exposure (see paragraph 1.5), as opposed to the land surface area exposed to flooding. Residential properties are assumed to be any property without an organization name in the Ordnance Survey Address Point data. This assumption is considered reasonable^[10].
• Use of an estimate of flood disadvantage restricted only to neighbourhoods with some coastal or fluvial flood-hazard exposure. This avoids neighbourhoods which are not exposed to fluvial or coastal flooding being shown as flood disadvantaged, as a result of averaging a very high socio-spatial flood vulnerability score with a low flood exposure score. This issue was not a particular problem for assessments based on larger geographical units. However, it was considered important to address for Scotland because of: the small size of the Scottish neighbourhood units; the relatively geographically confined characteristics of some of the flood types; and the very high values of socio-spatial flood vulnerability in some neighbourhoods. An important caveat should be noted, that the study does not include pluvial flooding - surface water flooding from rainwater. Inclusion of pluvial flooding will increase the number of neighbourhoods with high flood disadvantage scores.

2.6 A number of caveats apply to the assessment and its results. These are discussed at length in Lindley et al. (2011). The quantitative methodology was informed by an extensive literature review, but mapped neighbourhood characteristics can only provide part of the evidence base required for understanding and responding to individual and community social vulnerability. The construction of Scottish Data Zones takes some account of physical and social characteristics; that is, by delineating boundaries which follow "prominent features in the physical environment" and which represent zones which are broadly socially homogenous (GI-SAT; 2011: 3; HM Government, 2013). However, even where populations are small and unit boundaries carefully chosen, the broad characteristics of neighbourhoods can never be inferred for every individual within them. The main additional caveats associated with this work are the following:

• The flood area data do not account for flood defences and therefore over-estimate hazard exposure in some areas.
• The assessment does not take account of pluvial flood likelihood and therefore under-estimates hazard exposure in some areas. Inclusion of pluvial flooding will increase the number of neighbourhoods with high flood disadvantage.
• Version dates of the provided data are inconsistent (Table 1) and in some cases are considerably different to the indicators used in the socio-spatial vulnerability analysis (Table A1.2, Appendix 1). The latter are primarily based on data from the 2001 Census. Ideally, all data would refer to the same base year, but this is often not possible in studies of this type.
• There is no detailed consideration of residential addresses associated with flats and apartments.

2.7 The socio-spatial flood vulnerability index contains an indicator which estimates the potential ease of access to flood insurance across Scotland (Appendix 1, Table A1.2). It is constructed from area-based data within SEPA's Historical Flood Zone dataset. The area-based data are known to have incomplete coverage across Scotland. This study investigated whether point-based event data might provide a more suitable basis for the indicator. At the present time, the point-based historical flood events dataset is not considered to be a suitable basis for an alternative indicator of flood insurance access. The current dataset contains a lack of information for many events, incomplete geographical coverage and inconsistent reporting. These caveats in the dataset are well known to SEPA and reported on supply of data to potential users. Despite the limitations of its use within this particular study, the Historical Flood Zone dataset is considered a valuable resource which merits ongoing maintenance and further development.