Pluvial (surface-water) flooding
Intense rainfall overwhelming local drainage: the flooding that happens away from rivers.
The question it answers
Where could intense downpours overwhelm local drainage and pond around our assets, even well away from any river?
Screening pluvial (surface-water) flooding across a portfolio
- Screens assets for surface-water flood exposure driven by intense rainfall, not river overflow.
- Combines extreme-rainfall indices with terrain flow-accumulation and how built-up the location is.
- Bands the result and projects it across SSP scenarios and horizons.
Inputs in, banded result out
The governed model combines the inputs below into a single banded, scenario-aware result, under formal version and change control.
Inputs
- Extreme-rainfall indices (rx1day, rx5day)
- Terrain flow-accumulation
- Urban fraction
Governed model
Pluvial (surface-water) flooding
Anchored to public, peer-reviewed climate science.
Version and change controlledOutputs
- Asset risk band
- Scenario–horizon trajectory
- Portfolio roll-up
What goes in, and where it comes from
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Extreme-rainfall indices (rx1day, rx5day)
CMIP6
The rainfall intensity signal — maximum 1-day and 5-day totals.
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Terrain flow-accumulation
Global DEM
Identifies low points and drainage lines where surface water collects.
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Urban fraction
GHSL (Global Human Settlement Layer)
Proxies impervious surfaces that shed water rather than absorb it.
The futures we test
- Rainfall extremes are read per SSP scenario and horizon, capturing intensification with warming.
- Terrain and urban fraction are treated as the present-day setting the rainfall lands on.
- The result reflects surface-water ponding potential, distinct from fluvial river flooding.
How the result is built
- Read extreme-rainfall indices at the asset cell for each scenario and horizon.
- Weight by terrain flow-accumulation so low-lying, water-collecting sites score higher.
- Weight by urban fraction to reflect reduced infiltration in built-up areas.
- Combine into a composite score and band on the shared physical-risk axis.
What you get back
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Asset risk band
Surface-water flood exposure at screening resolution.
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Scenario–horizon trajectory
How exposure changes as rainfall extremes intensify.
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Portfolio roll-up
Pluvial exposure aggregated across the asset base.
- Low
- Medium
- High
Exposure trajectory for a single asset
Pluvial trajectories track rainfall intensification, which can rise sharply under higher scenarios.
How to read the band
- High pluvial bands cluster where intense rainfall meets low-lying, built-up ground — car parks, basements and yards, not just rivers.
- Because it is rainfall-driven, the trajectory can climb steeply under SSP3-7.0 and SSP5-8.5.
- Local drainage design is decisive and unmodelled here — treat High as a prompt for a site drainage review.
Disclosure relevance
- IFRS S2 Identification of acute physical risks beyond riverine flooding.
- TCFD Physical risk assessment across hazard types.
Limitations
- Screening scope: not a drainage or stormwater model.
- Drainage capacity, culverts and pumping are not represented.
- 0.25° rainfall inputs smooth the convective extremes that drive real surface-water events.
Related models
Services
Screening-level analysis; not investment or engineering advice.
Bring pluvial (surface-water) flooding screening to your portfolio
Screened, banded and framed for IFRS S2 and TCFD disclosure.