Hurricane risk assessment in a multi-hazard context for Dominica in the Caribbean

Abstract

Hurricanes can trigger widespread landslides and flooding creating compound hazards and multiple risks for vulnerable populations. An example is the island of Dominica in the Caribbean, where the population lives predominantly along the coast close to sea level and is subject to storm surge, with steep topography rising behind, with a propensity for landslides and flash river flooding. The simultaneous occurrence of the multiple hazards amplifies their impacts and couples with physical and social vulnerabilities to threaten lives, livelihoods, and the environment. Neglecting compound hazards underestimates overall risk. Using a whole island macroscale, (level-I) analysis, susceptibility scenarios for hurricanes, triggered landslides, and floods were developed by incorporating physical process parameters. The susceptibilities were combined with vulnerability indicators to map spatial patterns of hurricane multi-risks in Dominica. The analysis adopted a coupled approach involving the frequency ratio (FR), analytic hierarchy process (AHP), and geographic information system (GIS). Detailed hazard modelling was done at selected sites (level-II), incorporating storm surge estimates, landslide runout simulations, and steady flow analysis for floods. High-resolution terrain data and simulation models, the Rapid Mass Movement Simulation (RAMMS) and the hydrologic engineering center's river analysis system (HEC-RAS), were employed. Ground validation confirmed reasonable agreement between projected and observed scenarios across different spatial scales. Following the United Nations Office for disaster risk reduction (UNDRR) call for the inclusion of local, traditional, and indigenous knowledge, feedback, and expert opinion to improve understanding of disaster risk, 17 interviews with local experts and 4 participatory workshops with residents were conducted, and findings were incorporated into the analysis, so as to gain insights into risk perceptions. The study's outcomes encompass projections and quantification of hurricane compound hazards, vulnerabilities, accumulated risks, and an understanding of local priorities. These findings will inform decision-making processes for risk mitigation choices and community actions by providing a new framework for multi-hazard risk assessment that is easy to implement in combining different data forms.

Figure 1

Location of Dominica in the Eastern Caribbean.

Figure 2

(a) Hurricanes within 111 kms of Dominica for the period from 1851 to 2020; (b) intensity of the past hurricanes with track over Dominica; (c) track, intensity and wind radii of the Hurricane Maria 2017.

Figure 3

Intensity (kt) of hurricanes within 111 kms of Dominica from 1851 to 2020. The data has been obtained from the National Oceanic and Atmospheric Administration (NOAA) hurricane database.

Figure 4

Methodological framework adopted for the present study.

Figure 5

Multiple hazard susceptibility of Dominica: (a) hurricanes; (b) landslides; (c) floods; (d) composite hazard scenario of all the selected hazards. Pie graphs show area under each hazard category.

Figure 6

Storm surge scenario likely to emerge under 4 m water column, derived using Digital Terrain Model (1 m) and Google Earth data. The figure shows the areas that may submerge under the given surge conditions. Inset (b), (c), and (d) show the zoom-in view of the locations within black colour rectangles on the part ‘(a)’ of the figure.

Figure 7

RAMMS simulation results obtained under variable spatial resolution of digital topography products. This figure shows the variability in flow height, flow volume, and moving momentum of the landslides under different spatial resolution digital elevation models: (a) Shuttle Radar Topography Mission (SRTM) 30 m, (b) Advanced Land Observing Satellite (ALOS) Phased Array type l-band Synthetic Aperture Radar (PALSAR) 12.5 m, (a) NEXTMap One Digital Terrain Model (1 m); (a1), (b1), and (c1) show the flow momentum and flow volume corresponding to (a), (b), and (c) respectively.

Figure 8

Landslide runout simulations. Spatial patterns of deposition, maximum height, maximum velocity, maximum pressure, flow volume and moving momentum of debris under different friction parameters (μ and ξ) and release depth volumes ((a) 0.5 m, (b) 1.0 m, (c) 3.0 m). (a1) location of the selected slope and (b1) simulation results of 0.5 m release depth volume overlain on Google Earth image.

Figure 9

Steady flow simulation of the Roseau River using HEC-RAS. 3D terrain maps on the left show the location of particular cross-sections along the selected river reach; graphs show the water elevation at the highlighted cross-sections for Q 142 m³ (middle) and Q 850 m³ (right) respectively. Google Earth images depict the spatial patterns of water depth (a), velocity (b) and water surface elevation (c) for the given discharge rates. Arrows show the flow direction.

Figure 10

(a) Risk to population from the multiple hazards and (b) zoom-in view of the area shown in the box on a.

Figure 11

Ground validation points; (a) Surge simulation, location: 15° 19′ 38.4″ N 61° 23′ 42.8″ W; height of sea wall above high tide: 4.5 m, sea wall 1 m high on road side, road approximately 3.5 m above high tide mark; (b) bridge on Roseau River, location: 15° 18′ 07″ N 61° 23′ 10″ W, bank height on either side is approximately 5 m; (c) panoramic view of landslide simulation site (currently vegetated), location: 15° 14′ 13.2″ N 61° 21′ 20.0″ W, the building on extreme left is Soufriere Primary School, volume of the truncated cones at the base of the sites c1 and c2 is approximately10,000 m³.