Quantifying the Impacts of Flash Flooding on Dominica’s Material Stocks in Buildings: A GIS-based methodological framework for Small Island States

Abstract

Economic growth is usually accompanied by extensive extraction of natural resources, especially in developing countries. From a “material-stock-flow-service” perspective, the substantial part (e.g., construction materials) of the extracted natural resources as inflows to a society get accumulated in the built environment as “material stocks” (MS). Depending on the end-use types of their containers, MS provide essential services to a society such as housing, education and transportation. When an environmental hazard strikes, MS lose their functionality due to the destruction of the physical structure of their carriers, resulting in extra construction waste that then must be cleared for recovery. To make a society more resilient to environmental hazards, which is especially important in small island states with limited natural and human resources, the knowledge of exposure of MS to hazard risk is critical. This research focuses on the quantity and spatial distribution of MS in buildings in the context of intense rainfall-triggered flash flooding in Dominica, a small island state in the Caribbean region. A Geographical Information System (GIS)-based stock-driven methodology is used to quantify four typical types of construction materials: concrete, aggregates, timber, and steel. To quantify exposed MS in buildings to flash flooding, an event-based flood model is used to generate flood inundation extents at the national scale. To investigate the degrees to which the exposed households are susceptible to the impacts of environmental hazards, this research also designs a resident survey to collect social factors contributing to household vulnerability to hazards. For 2020, the total MS in the building sector is estimated at 6,574 kt, equivalent to 91 t per capita, given Dominica’s population of the year. In terms of the distributions of MS in different material categories, concrete accounts for 86% of the total MS in buildings, followed by aggregate at 7%, timber at 4% and steel at 3%. Examining the exposure of MS in buildings to flash flooding, it is found that flood events of larger magnitudes would result in more MS contained in the exposed buildings. For flash flood events with 5-year, 10-year, and 20-year return periods, the numbers of exposed buildings are 2,781, 3,030, and 3,274, respectively, which contain 17%, 18%, and 19% of the total MS in buildings in Dominica. This research demonstrates how to link the results of material stock accounting to flash flood modelling, approaching the concept of socio-economic metabolism from an environmental hazard risk perspective. Knowledge of the quantity and spatial distribution of the exposed MS in buildings can assist local governments in making cost-effective mitigation plans before a hazard event. Although the designed survey was not implemented due to travel restrictions, it is a valuable instrument to collect the information about household vulnerability to environmental hazards, which can help hazard response agencies with more-efficient rescue operations during a hazardous event.