Tutorials / Guided use cases
Floods in Great Abaco, a consequence of Hurricane Dorian hitting the Bahamas Islands
Hurricane Dorian was an extremely powerful and devastating Category 5 Atlantic hurricane, that hit the Bahamas in September 2019 and is regarded as the worst natural disaster in the country's history. Low-lying and surrounded by water, the islands of The Bahamas are overwhelmingly susceptible to flooding and have difficulty coordinating relief efforts in the wake of storms. Abaco and Grand Bahama, two major islands of the Commonwealth experienced the catastrophic impacts of this hurricane.
Natural disasters, Hurricane, Floods
The climatic, topographic, demographic and disaster related data assessed through the combination of Earth Map and the Imagery Compare Tool show some of the impacts of Hurricane Dorian on the island, such as flooded area and its drivers such as erratic rainfall and low elevation.
(i) The monthly precipitation and deviation (mm) graphic (Figure 1) between 1979-2019 shows a precipitation peak in September 2019 when category 5 Hurricane Dorian hit the country (310 mm rainfall in one month). Another precipitation peak appears in September 2004 when category 4 Hurricane Francis struck the islands of The Bahamas;
(ii) The elevation map (Figure 2) shows the low-lying Great Abaco Island whose elevation mainly ranges between 0 and 10 meters above sea level. Most of the island has little or no slope as seen in the slope map (Figure 3);
(iii) The location of high-density population areas such as Marsh Harbour in Great Abaco can be derived from the nigh light intensity map (Figure 4). Marsh Harbour, the Abacos' commercial hub that was affected by the floods can be easily spotted in the map;
(iv) Figure 5 illustrates the water occurrence between 1984-2018 and shows that some parts of the Great Abaco Island are sometimes flooded. The Sentinel 2 False colour mosaic satellite image in September 2019 (Figure 6) shows all flooded areas directly after the Hurricane hit the Island and displays some spots in black that do not appear in the water occurrence map;
(v) With the Area Measurement possibility of the Imagery Compare Tool (Figure 6, Sentinel 2 False colour mosaic satellite image in September 2019) we find that around 400 ha of land were flooded the first days of September around Marsh Harbour in the Great Abaco Island. This is one example of the catastrophic impacts of this hurricane.
Figure 6: Vegetation intensity in the northern part of the Great Abaco Island (based on Sentinel 2 - False colour mosaic (20 m, bands nir-swir1-red)). Orange represents high vegetation intensity; green low vegetation intensity and black and dark blue spots represent water. Above image in August 2019, below image in September 2019.