Pilot answer · Kibera, Nairobi
Check possible flood risk near you
Use the latest rainfall forecast to see possible hotspots, when conditions may worsen, and three actions you can take early.
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No precise location selected
We can use the centre of the selected sample area, or you can choose a precise point.
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Your coordinates stay on this device and are not shared.
Near your location
Planning result: Possible flood hotspots
Planning
Preparing your location-based result…
What you should do
Why this advice?
Forecast and model output support planning; they do not confirm flooding on the ground. Check official Kenya weather alerts
From terrain and rainfall to an early-action brief
How the model works
BlueSpot Alert uses terrain-based flood screening to identify where stormwater is likely to collect, when a low place may overflow, where that water may move next, and what those patterns mean near a selected location.
Bluespot, in plain language
A low place that stores rainwater until it becomes full.
Every bluespot has a contributing area that sends water into it, a storage capacity, and a pour point where excess water begins to leave. Once full, overflow follows the terrain to another low place. Many connected bluespots can therefore turn local ponding into a larger downstream problem.
The terrain model
Six steps from elevation data to flood exposure
Most heavy spatial processing happens before the app is opened, so a warning can be produced quickly during an emergency.
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Prepare the terrain
A 5 m elevation model is corrected so data noise, roads and embankments do not create unrealistic drainage. Building footprints are added as raised barriers so water is directed around structures.
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Find meaningful low places
The terrain is compared with a depression-filled surface. The study retained depressions deeper than 0.05 m and larger than 10 m³, filtering out likely terrain noise and trivial storage.
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Measure storage and catchments
For each bluespot, the model calculates depth, volume, the land area draining into it and the rainfall depth needed to fill it under the screening assumptions.
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Connect the pour points
Pour points and junctions become nodes. Downhill flow paths become edges, creating a directed network that shows how overflow can cascade from one bluespot to the next.
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Run rainfall scenarios
Rainfall over each contributing area becomes a water volume. Local rainfall and upstream overflow fill each bluespot; only the water above its capacity is passed downstream.
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Estimate exposure thresholds
Buildings and roads intersecting an active bluespot or nearby overflow corridor are flagged. The earliest rainfall scenario that activates each feature becomes its warning threshold.
The storage rule
The core calculation stays understandable
The BlueSpot Alert response layer
How the website turns the model into action
The map supports the answer. The default product is a location-specific brief that tells someone whether to act, when risk may increase and what to do next.
- 1Receive a rainfall signal
Use a manual scenario or the wettest forecast three-hour window. Forecast rain is matched conservatively to the next available modelled scenario.
- 2Check one location
Compare the selected point with nearby bluespots, spillover corridors, exposed buildings and road sections instead of showing the whole dataset at once.
- 3Explain timing and severity
Use precomputed thresholds and an illustrative three-hour progression to show when nearby features may become active. This is a scenario, not observed water movement.
- 4Choose verified actions
A deterministic safety engine produces resident, community-leader or responder guidance. Automated wording may simplify the alert, but it cannot change the modelled risk.
- 5Share and verify
Create a concise alert, open the focused map evidence, and check official warnings or field reports before operational decisions are made.
Current pilot-area scenario
What the selected rainfall scenario is showing
Strongest as a hotspot screen
98.5% precision
21.9% recall
0.357 F1 score
Areas flagged by the study were usually flood-prone, but the model did not reproduce every flooded location. It should support prioritisation, not replace a full hydraulic model.
What BlueSpot Alert has prepared
- 80 rainfall screening scenarios and 80 storm timelines
- 7,943 building footprints with exposure thresholds
- Five historical flood events for comparison
- Location, walking, driving and responder rules
Method reference Read the Arc-Malstrøm method
Important limitations
What the model cannot confirm on its own
This is a terrain-based susceptibility screen, not a live measurement of flood depth, speed or building damage.
- The terrain and building surface is a snapshot; construction, waste and informal drainage can change local flow paths.
- Scenario rainfall is simplified and does not represent street-by-street variation, antecedent moisture or every storm pattern.
- Infiltration, drain capacity, blockage, water velocity and detailed hydraulic behaviour are not fully simulated.
- Building exposure means spatial proximity to modelled water accumulation or overflow—not confirmed indoor flooding or damage.
- Official warnings, community reports and responder field verification take priority over the prototype.