How to calculate property damages from a flood depth grid

The Damage Calculator tool can be utilised to calculate property damages for both residential and non-residential properties. These data can be output in spreadsheet or shapefile format. In addition to calculating damages from a single model result, Damage Calculator can also process multiple results from the same scenario to calculate annualised damage values (AAD) and multiple results from multiple scenarios to also calculate present value damage data (PVD).

This section guides you through the process of using your flood depth grid model outputs to calculate likely damages to affected properties.

Note that this section assumes that you have already acquired a set of depth damage relationships in the required format. The tool has been developed in collaboration with the Flood Hazard Research Centre (FHRC), who are part of the University of Middlesex, UK (https://www.mdx.ac.uk/our-research/centres/flood-hazard ). The approaches in the tool follow FHRC’s 2013 publication: Flood and Coastal Erosion Risk Management: A Manual for Economic Appraisal more usually referred as the Multi-Coloured Manual (MCM). To support MCM approaches, FHRC publish an annual Handbook for Economic Appraisal (usually referred to as Multi-Coloured Handbook (MCH) and updates of property depth damage data referred to in the MCM. With the appropriate licence these data can be downloaded from the website; https://www.mcm-online.co.uk/ in a format that can be used directly in Damage Calculator. Alternatively, you can generate your own depth damage data in the same format (for guidance, a sample is provided as part of the Flood Modeller example data). Furthermore, this format is described in the user guide at 'How to setup my Damage Calculator depth damage curve data'.

To further extend your analysis to include calculation of AAD and PVD or to include customised property level protection within your damage data, see the following sections:

• How to calculate annual average damages
• How to calculate present value damages
• How to apply property level protection thresholds to my damage calculations

To calculate damages for a single depth grid output from a flood model:

1. Add an ASCII format grid of flood depth data to your current project. Grids should be the ESRI format, as defined here:
   https://www.loc.gov/preservation/digital/formats/fdd/fdd000421.shtml
   This may be a grid already created, in which case load in the Layers Panel using Add GIS data. Alternatively, this may be created by post-processing either 1D or 2D model results, using the relevant flood map calculator tool on the Results tab of the main Toolbar.
2. You will need a point shapefile or csv format text file that represents your property data. This can be added to your project if it is a shapefile (also csv files can be imported as new shapefiles), however it is not essential as you will have the option to browse to this file later in the process.
   Two main sources of property data available for use in flood and coastal erosion risk management in England and Wales are:
   • National Property Dataset (NPD)
   • National Receptor Dataset (NRD) Property Points Layer
     
3. Start the Damage Calculator tool from the Toolbox > Post Processing Tools section. You will be prompted to automatically preload any depth grids you want to use to calculate damages and also your property dataset. Select the depth grid you are analysing and your property dataset shapefile (if it is present in the Layers panel of your project).
   
4. After making any selections, click OK to proceed and the Damage Calculator tool will open in a new window (in front of Flood Modeller) after a few seconds. Any files selected in the previous window will be added in the appropriate locations within the interface.
   
   The property data file you specify needs to include particular attributes to enable the damage calculator to look-up the appropriate damage data associated to each property type. It is recommended that you always click the Field Mappings button to check the attribute fields in your specified file and also check how Damage Calculator has assumed these fields “map” to the required fields for the analysis. These field mappings are displayed in a pop-up window and this also allows you to modify the mappings and save these revised settings for your analysis.
   Note:

   If you are running this tool for the first time it is likely it won’t have a location stored for your depth damage curves data. In this case the tool will prompt you to specify a folder which should contain ONLY the required data files defining depth damage relationships for different property types plus some associated data. The required files should have the following names and content:
   

   • MCM Depth Damage Curve Scenario.csv – Provided by Flood Hazard Research Centre (FHRC). Dataset is part of the UK Multi-Coloured Manual (MCM). This file lists the scenarios for which depth damage data are provided, e.g. Short_NoW_storm, which represents a short duration storm event (<12hrs) with no warning. Other options to include in scenarios are contaminated water, saline water, wave impacts or sewerage. Note and example of this file (with just two property types included) is provided by Flood Modeller.
   • RP_DD_curves.csv – Provided by FHRC as part of MCM. This file lists the depth damage relationships for different types of residential properties. Curves are provided for some or all defined storm scenarios. Note an example of this file (with just two property types included) is provided by Flood Modeller.
   • NRP_DD_curves.csv – Provided by FHRC as part of MCM. This file lists the depth damage relationships for different types of non-residential properties. Curves are provided for some or all defined storm scenarios. Note an example of this file (with just two property types included) is provided by Flood Modeller.
   • MCMCode.csv – Provided by Flood Modeller (in the FloodModeller_ExampleData zip file included in the GUI installation folder – look in folder; “MCM example damage data folder”). This file lists the possible housing types that may be in your MCM depth damage curve files, with a cross reference to MCM code.
   • DefaultFloorArea.csv - Provided by Flood Modeller (in the FloodModeller_ExampleData zip file included in the GUI installation folder – look in folder; “MCM example damage data folder”). This file provides a default floor area for each property type (residential and non-residential). These data can be used to calculate damages for properties with no floor area specified in the property file. Note using this file is an option, alternatively you can opt to consider zero damage for properties with no floor area specified.
   • Occupancy.csv - Provided by Flood Modeller (in the FloodModeller_ExampleData zip file included in the GUI installation folder – look in folder; “MCM example damage data folder”). This file provides average occupancy figures for each property type. These data are utilised in the optional risk to life calculation within Damage Calculator (note this option also requires additional input data to be prepared, i.e. flood inundation data and flood hazard data).
   • PLPMeasures.csv – Example dataset provided by Flood Modeller. This file defines one or multiple property level protection measures. The description of the measure is listed here and the associated adjustment factors (in the PLPfactors file) are referenced. If you have these data in your data folder you have the option of calculating the effect of property level protection on damages.
   • PLPFactor.csv - Example dataset provided by Flood Modeller. This file defines adjustment factors to be applied to depth damage data for one or multiple property level protection measures. The same factors will be applied to all property types if you choose to analyse the effect on damages of a particular property protection measure (if you have these data in your data folder).
   • EvacuationCosts.csv - Provided by FHRC as part of MCM (“Mid” values taken from “Evacuation costs – full scale” tables in Chapter 4 of MCM online). The data here provide depth verses evacuation cost relationships for different residential property types (note bungalow property types have no data defined and thus are excluded from evacuation costs calculations – unless you first modify bungalow property types to something different). Evacuation costs vary with depth, however, unlike property damage, costs are not interpolated between the specified depths within each relationship (thus the defined relationships are stepped). Note an example of this file (showing the format, but with made-up values that must be changed before being used in an analysis) is provided by Flood Modeller.
   • MentalHealthCosts.csv – Example dataset provide by Flood Modeller. The data provide depth versus mental health cost relationships for different residential property types. Note that bungalow property types have no data defined and thus are exluded from mental health cost calculations, unless bungalow property types are first modified to something different. Mental health costs vary with depth. Unlike property damage costs, however, costs are not interpolated between specified depths – i.e. the defined relationships are stepped. The values in the example provided are from the UK environment agency document ‘Advice for Flood and Coastal Erosion Risk Management Authorities – Mental Health Costs of Flooding and Erosion’ (published 17/04/2020).

   Details on the format of the content of each of the above data files are provided in the section: How to setup my Damage Calculator depth damage curve data.

5. Specify an output folder where you wish your damage calculator results to be written. Results are generated in a series of csv format text files (that can be loaded directly into MS Excel), together with a “.log” text file that is generated as a log of your analysis. The log file provides a record of the associated metadata, e.g. input grids, analysis settings, plus any issues arising during the analysis, e.g. a list of properties with no type defined. The output folder can be typed or pasted into the available space. Alternatively, a button is provided enabling you to browse to a folder.
   
6. If you have not pre-selected a property shapefile (from your main Flood Modeller interface) then you need to use the adjacent browse button to specify either a shapefile or csv format file.
   
7. Select your depth damage data source. Depth damage data are provided in CSV format – supplied by Flood Hazard Research Centre (FHRC) in the UK. All depth damage files should be placed in the same folder and it is this folder that must be referenced within the Damage Calculator tool. The folder is referenced in the tool interface on the Settings tab. A button is provided to browse to this folder (see below).
   Guidance on how to define new or edit existing depth damage csv data files is available elsewhere in the user guide.
   Depth damage data files should contain data from a single year. The tool will read the year field for the first row of data and report this in the interface.
   
8. A set of MCM csv files will include multiple depth damage data curve sets. Each set will represent the combined effect of particular attributes of flooding. These are:
   • Year data was defined, e.g. MCM data are revised annually
   • Flood duration, e.g. 12hr or 21days
   • Warning – different damage curves are used to represent no warning, <8hr warning and >8hr warning
   • Saline – damages can vary if flood water is saline
   • Sewage – damages can vary if flood water is contaminated
   • With / without cellars – damages can vary if cellars are considered for certain property types
   • Wave – tidal flooding can vary damages due to wave affects (effectively increasing flood depths)
   Furthermore, each curve set provides depth/damage relationships for a range of different property types. These might be residential only, non-residential only or a combination of residential and non-residential.
   To select a curve set, go to the Depth/Damage Curves tab of the interface. This provides descriptions of the available variations within the selected data folder (the tool extracts these from the datafiles) and enables you to select a separate curve set for residential and non-residential properties, via two dropdown lists (as shown in the screenshot below). Note, the available variations are different for residential and non-residential property types.
   Your selected curve sets for both residential and non-residential properties are listed in the left-hand panel (in a tree view). You can expand any branch to drill down and access available sub-types for each of the main property types listed. The underlying depth/damage data associated to the selected (highlighted) row is plotted on the adjacent chart and listed in the adjacent table, as shown in the example below:
   
9. There are additional custom settings that can optionally be specified for your damage analysis. These are:
   • Calculate annual average damages – requires multiple depth grids as inputs.
   • Calculate present value damage – requires multiple depth grids from multiple scenarios as inputs. Also requires associated settings to determine appraisal period, interpolation method and whether to cap values to a market value. In addition, method uses customisable datasets to define market values (to cap against) and discount rates.
   • Calculate risk to life metric – risk to life data are calculated in the form of numbers of people affected and the corresponding incurred costs (based on the risk to life cost value specified on the Calculation Information tab – a default value is provided taken from: https://webarchive.nationalarchives.gov.uk/20130903160009/http://archive.defra.gov.uk/environment/flooding/documents/policy/guidance/fcdpag/risktopeople.pdf))
   This analysis also requires flood hazard grids and time of inundation grids to be added as input data, associated to each specified flood depth grid. Note this analysis option is only available when your input flood depth data are also in grid format.
   • Implement property level protection – requires separate data files detailing damage variation for each property type due to additional protection. These are required in csv format and located in the specified folder for your MCM depth/damage curves.
   • Include a global property threshold, i.e. depth must be exceeded before damages incurred (specified value subtracted from all input grid depths).
   • Calculate damages for upper floors of properties - uses upper floor code in property data (usually property points with this property will be excluded from calculations.
   • Interpret residential property sub-type codes – look at property metadata to try to determine precise sub-code of each property. If unticked then the code provided in the MCM code attribute field will be used (usually a more general code for the property type). If no code present in this field then property will be assigned zero damage.
   • Define alternative codes to apply for all properties of a specified type. This can be used to assign a standard type to all properties with no property type defined, i.e. with code 999 (so they contribute to the calculated damages). Alternatively, you could simplify an analysis by assigning all detached properties to the same code (i.e. set types 111,112,113, etc. to type 11).
   • Calculate selected additional damages related to property flooding. These are vehicle damage, evacuation costs, mental health costs, emergency services costs and indirect non-residential property damage. For all options the tool will also calculate AAD and PVD values as well as the associated damages from each event. Each of these options have associated settings to determine magnitude of these damages and when a property is written off, so no longer incurring any damage (all settings can be left as defaults). These analyses are described in detail in the additional damages section of this guide.
   • Project notes – a box is provided for you to type any text describing the analysis. Text entered here will be written to your simulation log file and your analysis summary file (if you save your analysis settings).
   More details on these custom settings are available here: What custom settings are provided for a Damage Calculator analysis.
10. Your damage analysis should now be ready to start. Either go to the Calculation Information tab and click the Run button in the bottom right corner or click Run in the upper menu bar. If you haven’t yet saved your analysis Damage Calculator will prompt you to do so (calculations are saved to an xml text format). The analysis will then perform an initial check of your specified settings. It may display one of the following warning messages if it finds any issues:
    • The defined appraisal period extends beyond the final epoch (scenario) – this warning is displayed when you are analysing multiple scenarios, thus enabling calculation of PVD. You must specify a PVD appraisal period (default is usually 100 years). If your last scenario is less than the specified appraisal period into the future, then this warning is displayed to inform you that the tool will need to extrapolate to calculate PVD.
      
    • Additional damages write-off AEP does not match any input grid AEP – the tool calculates some additional property related damages (see later in this guide). These have different write-off methods associated to them, including a method that looks for flood damage starting at a specified AEP (default is 33%). This message is saying there is no direct match to this AEP in your input flood data. If you proceed then the tool will just look for the next nearest (but larger) AEP dataset and use that to determine if write-off (of additional damages) will occur.
    You can decide to accept all settings as is and click past any warning messages. The analysis will then start. A progress bar will be displayed in a pop-up window detailing each stage of the analysis (i.e. reading inputs, calculating damages, etc.). Analysis can take seconds or minutes (depending on the size of the input grids).
    
11. On completion of an analysis, the results are displayed in two new tabs (entitled “Results per property” and “Results Summary”). The results per property table combines the key attributes of each property identified within the flood extent with the calculated depth and associated damage. The total damage is also displayed below the relevant column in the table. If multiple grids are included in the analysis then the results table will contain multiple depth and damage data in extra columns, together with an AAD value. If they have been requested, PVD data are also reported in this table (in the columns preceding the depth, damage and AAD data).
    
    The Results Summary tab displays all column totals, i.e. damage, additional damage, AAD and PVD totals for all properties in your analysis area. Note, the property damages are displayed here as separate totals for residential and non-residential properties. In addition, the summary tab also displays wet property counts and totals for any additional damages requested.
    
    The tool writes these tabular results data to a series of csv format text files when the Export Results button is clicked (on the Results tab). One file contains all data displayed on the Results tab and one contains all data displayed on the Results Summary tab. These data will also automatically open in Excel when the Export Results button is clicked. Note that, if a PVD calculation is performed, an additional csv file is generated that provides a check of the contributions to PVD for each year of the specified appraisal period. This lists all discounted, interpolated AAD values (over the appraisal period) that are summed to calculate PVD totals for each property.
    Clicking the Export to Shapefile button will generate a new point shapefile with each point corresponding to a row in the currently displayed data, with the displayed tabular data included as feature attributes. These data can also be automatically added to your Flood Modeller map view by ticking the View in Flood Modeller checkbox prior to exporting (this option only works when you start Damage Calculator from within the Flood Modeller interface).
    The export buttons are located below the table on the Results tab.
12. If you right-click on any header within the results table you can access tools to customise the displayed data.The available tools are as follows:
    1. Sort the table using the selected column in ascending or descending order, e.g. to show the properties contributing most to overall damage totals. Note that simply clicking on a column header will also run the sort function (first click sorts in ascending order, second click re-sorts to descending order).
    2. Group by selected column – grouping by a selected column converts the table to a tree view in which each branch contains rows with the same value for the selected column, e.g. group by MCM code to see all properties assigned code 1. Branches can be expanded or collapsed either by clicking the triangle icon to the left of each group or by selecting new right-click menu options to expand/collapse all. Note that all groups will be collapsed initially, as shown in the example below:
       
       You can group by multiple columns. Grouping extra columns will create a nested tree view.
       The “Show Group By Box” command displays the selected column that defines the displayed groupings in a header above the table.
       Selecting the right-click option on a column header to Ungroup will return the table back to its original format.
    3. Show / hide columns – either user menu command to hide the selected column or display the column selection pop-up window as shown below. This can show/hide columns by dragging into the box or double-clicking on an item in the box already respectively. It can do the same for whole bands of columns, e.g. hide all property metadata columns copied in from the input property dataset.
       
    4. Filter editor – create expressions to define which rows in the table to display, e.g. only show properties with 100yr return period damages > 50,000.
       
       After filtering your results table, if you choose to export data to a point shapefile then only the displayed data will be exported. Hidden rows and columns will not be included in the shapefile.
13. Each damage analysis performed generates a log file in your specified output folder. The contents of this can also be viewed in the Damage Calculator interface on the Output log tab. This log file will include a summary of your analysis settings and any notes describing the simulation (added in the Project Notes section of the interface).In addition, any issues during the analysis are listed, e.g. where a property’s (MCM) code did match any of the curves included in the nominated depth damage database.
    
14. After completing your analysis, you can save the settings you specified to an xml format settings file, referred to as a Damage Calculator calculation file. Click the File menu in the upper left corner of the interface and select Save Calculation from the dropdown menu.
    Use the File menu to then reload a calculation file to review or repeat your analysis in a later session. Note that many of the default Damage Calculator settings (e.g. nominated depth damage data folder) will be stored by the tool and be present by default at the start of your next session.