Saint Lucia - Landslide Susceptibility Map - CHARIM

The aim of this study was to generate a national‐scale landslide susceptibility map for Saint Lucia. As the available data turned out to be insufficient to generate reliable results, we decided to generate several new data layers, and significantly improved some of the existing data. We generated a new database of disaster events for Saint Lucia, making use of many different sources.

This is the most complete inventory to our knowledge. It is quite clear from this database that the landslide reporting became more frequent in recent years, and less information on landslides is available when going back in time, whereas the data on tropical storms and hurricanes seems to be much more constant over time. The underreporting of landslides is a big problem in trying to evaluate and slide frequency/magnitude relations.

We also compiled all available landslide occurrence data from different sources. For received great support from the British Geological Survey, as a team from BGS generated new landslide inventory maps for 2010 to 2014 using high resolution satellite images in the framework of the European Space Agency (ESA) “eoworld 2” initiative. Eventually we compiled landslide inventories for 1985, 1995, 2009, 2010, 2011, 2012, 2013, and 2014. The resulting landslide database contains 430 landslides in 1985 (Hurricane Allen), 713 in 1995 (Tropical Storm Debby), 27 in 2009, 1025‐1132 in 2010 (Hurricane Tomas), 489 in 2011, 198 in 2012 and 459 in 2013 (Christmas Eve storm).

The manual editing of the susceptibility map was also done to simplify the susceptibility units. In the final landslide susceptibility map, 50% of the area was classified as low susceptibility, 24 % as moderate, and 26 % as high susceptibility.

When considering the landslide density, the values for low range from 0.0003 to 0.001, for moderate from 0.0014 to 0.006 and for high from 0.006 to 0.04. In terms of numbers per square kilometre, these values are 0.1 to 0.4 for low, 0.2 to 1.3 for moderate and 1 to 9.6 for high susceptibility. The ranges reflect the expected densities for frequent to rare events. It was very difficult to determine the frequency of the landslide densities due to a lack of sufficient event-based inventories.

We have separated four types of events: frequent, moderate, large and major events.