Somalia Flood Mapping Tool

Metadata

1. Flood Prone Areas

The flood prone layer was derived from combining historical floods layers that were generated from radar images (Sentinel 1) and the optical images (sentinel 2,landsat, and world view VHR Images).The analysis period was 1968-2020 and was done by SWALIM GIS & Remote sensing, Hydrology and meteorology expert in conjunction with SWALIM field human resource network.

Here is a summary of the precise details:

1. Google Earth Engine Script was used to extract flooded area from Sentinel 1 from 2014 to Present.

2. Flood exents extracted from optical images was through visual analysis of Sentinel 2 were from 2015 to present. Due to the presence of cloud cover, a combination of Landsat and World View 1 images were used as a complement.

2. Flooded Area

The flooded area layer was derived from Radar Images (Sentinel 1) and Optical images (Sentinel 1, Landsat and World view VHR images). This layer contains data from 2013 to Present. Some seasons like, 2020:Deyr did not record any floods. On the flipside,Flooding was experienced in dry seasons like 2020:Hagaa.

3. Reported Floods

Data is collected from the field using the Open Data Kit mobile applications. The data contains photos of the flooded areas and a brief description of the situation e.g. names of villages affected. This data is submitted to the database and visualized in the web map section of this application. Overlaying the photos with flooded area extracted from satellite images act as a form of verification.This data is divided into two: "Aware" and "Witnessed floods". Witnessed floods is collected when the data collector is in the vicinity of the flooded area. Aware floods is collected when the data collector is not in the vicinity of the flooded area but he/she has the knowledge of the location and the village that is flooded

4. River Breakages

The Juba and Shabelle rivers of Somalia have fertile soils and abundant amount of water that allows irrigated agriculture to be carried out throughout the year, making the riverine areas of the two rivers traditionally the bread basket of Somalia. However, the two rivers are prone to flooding mainly because the bulk of their flow originate from the Ethiopian highlands, which receives very high rainfall during the rainy seasons. Additionally, farmers break the river banks to get water to their farms during the dry season. To minimize impacts of flooding, FAO SWALIM has developed a system for monitoring river breakages along River Juba and Shabelle by analyzing very high resolution images. The system started in 2014 and provides data and information on river breakages including potential, open and closed breakages.

Display flood extent

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Boundary

River

Floods

Flood Prone

OPEN (O): Breakage point where a recent (< 1 year) flood originated is still open, and has no signs of intervention/rehabilitation on the latest analyzed images.

OVERFLOWS (Of): Portion of the river embankment where water overflows have recently occurred (< 1 year). Overflows generally take place along shallow portions of the embankments, which could be submerged for several hundred meters during the flood.

POTENTIAL (P): A point along the embankment where there is potential for flooding to occur. Clear indicators of flood potentiality, such as recent vegetation removal, embankment erosion, closed with sand bags, water spillage or other signs representing a potential embankment weakness have been identified. These indications are supported by DTM analysis, multi-temporal analysis and/or direct field observations.

Closed (C): Breakage point where an old (>2 years) flood originated and that has been fixed using either heavy machinery or sandbags. No flooding has been detected recently, so this point may be considered CLOSED as the situation is stable. Interventions by heavy machinery are permanent, while those by sandbags are temporal, subject to new floods.