Hazard models
Climate scenarios tell you what the weather is doing. Hazard models tell you what that weather does to a place.
In one sentence
Hazard models are computational or analytical tools that characterise the spatial extent, intensity and temporal evolution of natural or climate-related hazards.
Their job is translation. They take environmental drivers, such as extreme rainfall and temperature, and turn them into quantitative representations of hazard characteristics: not "it rained heavily" but "water was 0.4 m deep on this stretch of road at 08:20."
The two hazards DARe models
Within the DARe framework, hazard modelling focuses on two climate-related hazards that matter most for transport infrastructure and networks.
| Hazard | What the models produce |
|---|---|
| Flooding | Flood depth and extent |
| Heatwaves | Heatwave intensity and duration |
That output is deliberately shaped for what comes next. Because it is spatial and temporal, it can be integrated with infrastructure and transport models to assess exposure, disruption and wider system impacts, and to support climate resilience and adaptation assessment.
The three models
Flooding is handled by one model. Heat takes two, working in sequence at very different scales.
| Model | Hazard | Resolution | What it answers |
|---|---|---|---|
| CityCAT | Flooding | Grid cell, every 20 minutes | Where is the water, how deep, and when? |
| UrbClim | Heat | 100 to 200 m, hourly | How hot is this neighbourhood? |
| HiREx | Heat | 1 m, selected days | How hot is this spot on this pavement? |
Why heat needs two models
The scale jump is the reason. Urban heat behaves differently depending on how closely you look.
At neighbourhood scale, what matters is the urban heat island: the way a built-up area holds warmth that surrounding countryside sheds. UrbClim captures that.
At street scale, what matters is shade. Whether a person is standing in the sun or in the shadow of a building or a tree can swing their experienced heat load dramatically, and no 200 m grid can see that. HiREx resolves it at metre scale.
Run in sequence, UrbClim provides the urban meteorology that carries the urban heat island signal, and HiREx translates that into the micro-scale heat exposure a person actually experiences at street level, where building and tree shade dominate.
What this chapter covers
| Page | What you will find |
|---|---|
| CityCAT | The urban flood model, its four inputs, and its time-series flood maps |
| UrbClim | The urban climate model, the shared input datasets, and its gridded meteorology |
| HiREx | Metre-scale heat exposure, and how representative days are chosen |
| Further reading | Source papers and the geospatial datasets behind them |
Where this sits in the framework
Hazard models are the third step of the weather event component, taking their forcing from climate scenarios and handing their output to transport thresholds, which decide when a hazard becomes a transport problem.