What a flood map actually is
A flood risk map is a model, not a photograph. It combines elevation, drainage, rainfall records and past floods to estimate the chance an area floods. It says probability, not prophecy: a '1 in 10 year' zone can flood twice in one year.
Models are only as good as the data fed into them. Remember that sentence. It is the whole lesson.
Who is on the map
Informal settlements are often missing from official maps entirely. If your street was never surveyed, your flood is not in the model, so your risk is officially invisible. Population estimates for Makoko alone range from tens of thousands to hundreds of thousands, depending on who counted and why.
Data gaps become policy gaps. Drainage budgets follow maps. If the map skips your community, so does the money. This is climate injustice in its most bureaucratic form: nobody decided to harm anyone, and the harm arrives anyway.
Ground-truthing
The correction for a blind map is local knowledge, collected carefully. Photograph the waterline after a flood, with a date. Note which streets became impassable and for how long. That is data, and it is data only you can gather.
Cylin ambassadors do exactly this in workshops. A community that documents its own flooding can contest a map that ignores it.
Hold on to these
- Flood maps are models built from elevation, drainage and past records. They estimate, not predict.
- Unmapped communities are officially invisible, and budgets follow maps.
- Local documentation with dates and photos is real data that can contest a blind map.
Check yourself
No grades here. If you can answer these out loud, you own the lesson.
- 1.Why is a flood map a model rather than a fact?
- 2.Explain how a data gap becomes a policy gap, using Makoko as the example.
- 3.What three things would you record to document a flood on your own street?