# Flood depth-damage functions

**Example**: Vulnerability curves relating flood water depth to expected damage ratios or absolute losses, derived from statistical analysis of historical flood impacts.

## Step-by-step guidance

### 1. Dataset-level metadata

Select the following values when describing your dataset:

- **Risk data type**: `vulnerability`
- **Title**: "Flood depth-damage functions for \[asset types/region\]"
- **Description**: Brief description of the damage functions, asset types covered, and data sources used for calibration
- **Publisher**: Organization or research institution that developed the curves
- **License**: Appropriate license

### 2. Resources

Add resources for your damage function files:

- **Format**: `csv`, `json`, or `xlsx`
- **Spatial resolution**: Not applicable (functions are asset-type specific)
- **Coordinate reference system**: Not applicable

### 3. Vulnerability metadata

Under the Vulnerability section:

#### Category

- **Category**: `vulnerability`

#### Hazard type and intensity

- **Hazard type**: `flood`
- **Hazard primary type**: `flood`
- **Processes**: Select applicable process(es):
  - `fluvial_flood`
  - `pluvial_flood`
  - `coastal_flood`
- **Intensity measure**: Typically `fl_wd:m` (flood water depth in meters)

Additional intensity measures (if applicable):

- `v_fld:m/s` (flow velocity)
- `fl_fd:m3/s` (flood duration)

#### Vulnerability functions

For each asset type, create a function entry:

**Function specification:**

- **ID**: Unique identifier (e.g., `DF1_residential_1story`)
- **Relationship**: `vulnerability`
- **Function type**: `continuous`, `discrete`, `polynomial`, or `empirical`

**Damage scale:**

- **Type**: `relative` (damage ratio 0-1) or `absolute` (monetary value)
- **Unit**: `ratio` (0-1 or 0-100%) or currency code (e.g., `USD`)

**Function parameters:**

- For polynomial/continuous: coefficients and equation form
- For discrete: water depth bins and corresponding damage ratios
- For empirical: look-up table of depth vs. damage values

#### Asset taxonomy

Link damage functions to asset types:

- **Taxonomy source**: `GED4ALL`, custom, or building classification system
- **Taxonomy code**: Specific code for each asset type
- **Occupancy**: Residential, commercial, industrial, etc.

#### Cost information

Specify what is being measured:

- **Cost dimension**: Select applicable:
  - `structure` (building damage)
  - `content` (contents damage)
  - `business_interruption` (indirect losses)
  - `total` (combined)
- **Cost unit**: Currency code (e.g., `USD`, `EUR`) or `ratio` for relative damage

### 4. Spatial coverage

Define applicability:

- **Scale**: `global`, `national`, or `regional`
- **Countries**: Select applicable ISO 3166-1 alpha-3 country codes if region-specific
- **Description**: Note if curves are calibrated using local historical flood data

## Example data structure

Your damage function file should include:

**For continuous functions:**

- Asset type
- Occupancy category
- Flood depth range (min, max)
- Function type/equation
- Parameters/coefficients
- Damage dimension (structure, content, etc.)
- Units

**Example CSV structure for discrete functions:**

```
Asset_Type,Occupancy,Depth_m,Damage_Ratio_Structure,Damage_Ratio_Content
Single_family_1story,residential,0.0,0.00,0.00
Single_family_1story,residential,0.3,0.10,0.15
Single_family_1story,residential,0.6,0.20,0.30
Single_family_1story,residential,1.0,0.35,0.50
Single_family_1story,residential,1.5,0.50,0.70
Single_family_1story,residential,2.0,0.65,0.85
Single_family_1story,residential,3.0,0.80,0.95
```

## Key considerations

- Clearly document the derivation method (empirical from insurance claims, expert judgment, modeling)
- Specify the currency and reference year for absolute damage values
- Include information about the historical events used for calibration
- Document assumptions about building values or replacement costs
- Note whether functions include damage to structure only or structure + contents
- Specify if flood duration or velocity effects are considered
- Include uncertainty information if available
- Reference source publications or insurance databases
- Clarify whether functions assume presence of flood adaptation measures