Abstract
Urbanization has been linked to destructive geo-hazards that can cause loss of life, destruction of property, and environmental damage. On August 14, 2017, a devastating geo-hazard chain—a debris slide, debris flow, and sediment-laden flood—in Freetown, Sierra Leone resulted in at least 500 deaths and over 600 missing persons and the destruction of hundreds of houses. This study uses 10 years of high-resolution satellite images to conduct a remote sensing analysis of the disaster. Although rainfall was the trigger, rapid and haphazard urbanization acted to increase both hazard and vulnerability. Specifically, poor urban planning with inadequate consideration of risk led to housing construction in dangerous areas; clearance of hillside vegetation increased erosion potential; very low cost buildings using frail construction material and methods lacked resilience; and insufficient risk management led to weak emergency response.
Highlights
Urbanization is the process of human migration from rural to urban areas (Goryakin et al 2017) and involves change of land use from agricultural to non-agricultural (Li et al 2017)
This study examines how rapid land use change and haphazard urbanization acted as a catalyst for the Freetown disaster
The results indicate total rainfall contributing to hazard occurrence was 494.6 mm, of which triggering precipitation (TP) contributed 84.8 mm, direct antecedent precipitation (DAP) contributed 44.1 mm and indirect antecedent precipitation (IAP) contributed 365.7 mm
Summary
Urbanization is the process of human migration from rural to urban areas (Goryakin et al 2017) and involves change of land use from agricultural to non-agricultural (Li et al 2017). This study examines how rapid land use change and haphazard urbanization acted as a catalyst for the Freetown disaster This case might be considered an archetype example and a warning regarding a problem that is widespread in developing mountainous regions around the world. Freetown is a mountainous, hazard-prone area where at least six landslides have occurred between 2014 and 2016 (ESRI ArcGIS online 2018) For this disaster of 2017, natural factors such as heavy rainfall, steep slopes, intensely-weathered plutonic rocks, and abundant unconsolidated soil are major causal contributors of the Freetown cascading geo-hazard undoubtedly. Human activity is the critical factor for rapid, unconstrained development of exposure and vulnerability, and the principal causes of the heavy loss of life and building damage are land use change and haphazard urban expansion within an area that was already hazard prone. Landsat remote sensing images of Freetown in the dry season, obtained from the United States Geological Survey (USGS 2017), were used to identify land use changes between 2007 and 2017 at
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