Identifying settlements of high risk of floods in Greater Monrovia, Liberia.

Sofia Gonz
Jul 16 · 3 min read

I explored local risk to floods in Monrovia, Liberia for #VizRisk Challenge. An amazing experience by @UnderstandingRisk Mapbox World Bank @GFDRR @Openstreetmap


In the last decade, Monrovia has been severely affected by floods. In a city where large part of the population is homeless and most settlements are informal, the impacts of floods multiply the risk of sanitation issues and increase of disease transmission.

Flooding in Monrovia. Source: OPEN DRI

Identifying the settlements in Monrovia with higher risk to be affected by floods can help design and implement projects and policies that will help reduce the vulnerabilities such areas.

Methodology

  1. Collected open access data from Human OpenStreets Map, UNOCHA, and satellite data.
  2. Used QGIS to explore three main variables:
  • Distance from water bodies
  • Elevation
  • Population Density
QGIS Map of distance to water bodies.
QGIS Data Elevation Model.
QGIS Population Density Model.

3. I used statistical and geoprocessing tools in QGIS to combine the value of the variables to quantify a normalized scale of risk (Lowest Risk: 0 , Highest Risk: 1).

4. The resultant risk values were mapped using Mapbox and Tableau to create an interactive visualization were we can identify settlements of high risk. (Click link below).


In the map we can play with the interaction of two data sets.

  1. Flood Risk — Scale Green (Lowest) to Red (Highest Risk)
  2. Population density: the circle size represent the population density in each settlement.

If the mouse rolls over each circle the pop up shows the name of the settlement and the risk and population ranking.

It is very important to identify the flood potential impact across different areas in order to be able to understand risk and causes of vulnerability. In the previous analysis, data shows that areas with high flooding risk have as well high population density, amplifying the negative impacts on the citizens of Monrovia. This map could help policy makers to target the neighborhoods that present the higher risk, such as Clara Town, West Point, Vai Town, and Monrovia, in order to prioritize resource allocation and policy implementation.

Open data and mapping technology are incredibly useful to explore and make a preliminary analysis of the area, however in order to be able to perform an accurate analysis that can suggest solutions further onsite analysis and surveys are necessary.

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