Researchers from the ITC Faculty of Geo-Information and Earth Observation of the University of Twente have presented a large scale inventory of landslides of hurricane-hit Dominica.
Most destructive in decades
Hurricane Maria which hit Dominica on September 18 2017, is regarded as the most destructive natural disaster that has affected Dominica in the last decades. The hurricane killed 30 people (and 34 were declared missing). According to the Post-Disaster Needs Assessment Hurricane Maria resulted in total damages of EC$2.51 billion (US$931 million) and losses of EC$1.03 billion(US$382 million), which amounts to 226 percent of 2016 gross domestic product (GDP).
Maria damaged most of the houses, farmland infrastructures and left the mountainous country blanketed in a field of debris. High intensive precipitation triggered widespread floods as well as a tremendous number of landslides.
Inventory
A large scale landslide inventory was carried out by a team from the University of Twente, use of 5 scenes of Pléiades satellite imageries with resolution of 0.5m, which were obtained in September 23 and October 5 after the hurricane, made available through UNITAR-UNOSAT.
Apart from these also a series of Digital Globe Images were used that were collected for the Google Crisis Response through a KML layer. The images were visually interpreted by image interpretation experts, and landslides were mapped as polygons, separating scarp, transport and accumulation areas, and classifying the landslides in types. Unfortunately, due to cloud coverage in all available images.
A total of 9,960 landslides were identified, which include 8,576 debris slides, 1,010 debris flows and 374 rock falls, with area of 7.30km2, 2.50km2, and 0.50 km2 respectively. The whole area of landslide is 10.30 km2, which covers 1.37 percent of the island. The source of landslides is 3.30km2, and the other 7.0 km2 is transportation and deposition area. Almost all of the rivers flooded due to intensive precipitation. The flooded area is 13.03km2, which covers 1.74% of the island.
Future
Dominica will face some new problems for mountain hazards in the coming years, as many of the fresh scarps may produce more debris, and many tree trunks are still on the slopes or in the river channels. With so many fresh landslides in the upper catchments, it is likely that debris flows will be triggered with rainfall thresholds that are substantially lower than before the hurricane. Hurricane Maria damaged the forest cover dramatically, which changed the conditions for hazard initiation.
Without the protection of vegetation, more new shallow landslides could happen in the near future. A series of cascading hazards may happen, for example landslides or debris flow blocking rivers and resulting in outburst floods. Therefore more detailed evaluation of the post-Maria hazard and risk situation is very important.
A larger version of the map may be downloaded here (in PDF).
