Cities face frequent flood disasters with devastating impact on lives and property. Geospatial analysis using high elevation points can help to map out emergency evacuation centres for decision making on flood risk management. This research maps and analyses flood emergency evacuation centres in Accra. The objectives of this research were to map out flood hazard and vulnerable settlements, analyse the spatial distribution and identify the optimal locations for flood emergency evacuation sites. The data for this study comprises digital elevation models, stream networks, settlement data, flood risk zone maps of the study site and existing documents on flood disaster risk of the study area. This study adopted the weighted linear combination method to estimate site suitability for emergency evacuation sites. ArcGIS 10.6 was used to analyse the data. The research found that the optimal locations for potential evacuation centres are unevenly distributed between 300 m and 400 m above sea level, most which are in the north-eastern and north-western parts of Accra. The results can contribute to research, policy and decision-making on flood risk management in Accra and other localities with similar conditions. The research further contributes to literature on flood risk management and geographic information system.
This research is useful as mapping could increase awareness of evacuation sites to speed up rapid response to immediate impacts of flood events. The findings of the study will facilitate future decisions for demarcating potential flood emergency evacuation sites. The overall aim of this study is to contribute to literature, policy, spatial analysis and the practice of flood risk management in the study area. The research findings can also be applied to other flood-prone areas with similar contexts as the study site.
Flooding constitutes one-third of natural disasters globally, and the risk of future floods is increasing because of climate and societal developmental changes (Jha, Bloch & Lamond
The city of Accra in Ghana faces chronic floods with high recurrent impacts, thus impeding socio-economic development (Aboagye
Apparently, no studies captured the element of emergency evacuation sites in relation to the flood-prone neighbourhoods in Accra. A GIS mapping and spatial analysis of emergency evacuation sites is useful for emergency flood response planning in Accra. Scholars argue that GIS mapping and analysis about distribution of emergency evacuation sites is critical in planning for rapid response to flood impacts on humans and movable property (Kourgialas & Karatzas
The specific objectives of this research are to:
map out flood hazard and vulnerable settlement in the Accra Metropolitan Assembly
analyse the spatial distribution and identify the optimal locations for flood emergency evacuation sites of flood-prone neighbourhoods in the Accra Metropolitan Assembly.
The Accra Metropolitan Assembly in the GAR of Ghana was chosen for this research because of its chronic annual flood disasters in recent years. Rain et al. (
Study area.
Data for this research were obtained from existing sources. The data for this study consisted of digital elevation models (DEMs), stream networks, settlement data, shapefiles of Ghana, flood risk zone maps of the study site and existing documents on flood disaster risk of the study area. Existing documents include literature such as Nyarko (
Where Score = summary suitability score for the location,
Siting of evacuation centres depends on both social and physical factors. However, some factors are necessary and critical for the siting of an evacuation centre. Specification of the factors usually depends on the type of disaster in question. For instance, specific parameters are required for the siting of an evacuation centre in order to deal with the situation during a particular type of disaster. Disasters such as earthquake, fire, hurricanes and flooding require emergency evacuation sites that need to be strategically located. For this reason, highland areas are considered a critical potential parameter in the event of an emergency situation because of flooding. For this study, the terrain of the study area was considered a critical factor for the siting of emergency evacuation centres that will cater for emergency situations during flooding. Both physical and social factors influence the site suitability of an evacuation centre. However, based on the type of disaster at the study site, a research which has analysed and established the criteria for flood emergency evacuation sites is unclear.
The land use types, road network, proximity of the site to flood zones and DEM of the study area were considered useful for analysis. Following the WLC method for site selection, the factors for suitability analysis were given weights and ranked in order of importance of each of the factors. The weights assigned to these factors were elevation 50%, land use 20%, road network 15% and flood-prone areas 15%. Elevation was considered most important to have at 50% because it is a baseline for establishing safe havens during flooding situations. Next in the order of importance is land use, which was ranked 20%. Land use is given this rank because different land uses offer various ecological functions and importance. Thus, not every land use can be destroyed in order to site an evacuation centre. Road network and flood-prone areas were given 15% each, indicating similar ranks for importance. Road networks play important functions for evacuating life and property to safe havens, and it is critical to consider nearness to roads in the siting of emergency centres. Flood-prone areas signify settlements that are vulnerable to flood hazards. Thus, emergency evacuation centre sites need to be located near flood-prone areas of the study site.
Four data sets were used in this study to locate suitable areas for emergency evacuation sites during flood disasters as the main objective of the research. The majority of the study area is in flood-prone zones, so the driving factor for the siting of an evacuation centre in such an environment is the terrain of the study area. Other driving factors that were considered include the flood-prone areas within the study area, the land use types and road network (
The geospatial data used in this study.
Data | Description | Format | Source |
---|---|---|---|
Land use | Urban areas, crop land, forest, water bodies | Raster | Interpretation of Landsat satellite data by authors |
Elevation | Digital elevation model | Raster | United States Geological Survey (USGS) Earth Explorer website |
Flood-prone areas | Refers to high risk areas of flooding within the study area | Vector shapefile | Nyarko |
Roads | Road network of the study area | Vector shapefile | Centre of remote sensing and geographical information systems (CERGIS), University of Ghana |
Evacuation sites.
This study was conducted based on review on the rigorous literature review and GIS data. All academic research protocols including all works and data used in this article were acknowledged and cited. No plagiarism was performed and the article is mainly for academic purposes. This article did not involve animals and human subjects or participants and therefore did not need ethical clearance.
Flood risk describes an overlapping area of flood hazard and flood vulnerability (Nyarko
Workflow of data processing.
Flood-risk zones of the study area.
A digital elevation model is useful for topographical analysis and important for identification of lowlands and highlands. This is an initial step in gauging where evacuation sites can be located in the study area. Emergency evacuation sites are usually on high ground, safe from flood hazards, and this is a criterion for selecting high elevations for this research.
Digital elevation map of the study area.
In determining the locations for the evacuation sites, a set of criteria for site selection and suitability analysis was considered in this research. Several factors such as high elevation, flood-prone communities and access to transportation networks, health facilities and other facilities were given weights in selecting sites for emergency evacuation sites (Mustaffa et al.
On this basis, one can argue from
Emergency evacuation sites are part of disaster-risk management planning, and this project focuses on mapping of potential sites for evacuation of property and victims of flood disasters. The results revealed that flood occurs in lowland areas of settlements within drainage basins of the study site.
The flood-prone communities are along the stream networks. The south-western part of
Flood-risk zones and closest evacuation sites for flood-prone communities.
In order to get the best sites for the evacuation centres, the DEM was considered together with the land use, flood-prone areas and road networks of the study area.
Suitability of sites for flood emergency evacuation centres in Accra in the metropolitan assembly.
In
This research used GIS to map flood emergency evacuation sites of flood-prone neighbourhoods in the AMA in the GAR. Flood-prone communities of the study area were identified following the settlement map and confirmation of studies that mapped out the flood risk zones of the AMA. The DEM of the study site was then developed to show the topography and the stream networks of the study site. The highland areas within and around the flood-prone neighbourhoods were identified as points for emergency evacuation during flood events in the AMA. The distribution of these was interpreted to address the objectives of this research.
The results of this research are relevant for emergency flood risk management planning and allocation of emergency evacuation sites for flood-prone areas of the AMA. The research can also provide relevant literature for future research on GIS analysis of flood risk management of the study site and other areas with similar issues. A key finding of this study is that emergency evacuation sites are not evenly distributed across the study site. The potential points for location of evacuation sites are in the eastern, northern and western parts of the AMA.
The researchers acknowledge that this study has limitations that need to be outlined. The research was limited to flood-prone neighbourhoods of the AMA in the final analysis and only employed GIS tools for the study. The study relied on secondary data from existing sources. Although the secondary data came from reliably credible sources, primary data would have complimented the secondary data for a more comprehensive analysis.
From the results and the limitations of this study, the following recommendations can be made for emergency flood risk management planning policy and future research. For practical responses to emergency flood disasters in the AMA, this research recommends that emergency evacuation sites need to be established in and around elevations of 300 m – 400 m above sea level as safe havens. These elevation points fall within very low flood risk zones in the AMA. It is recommended that future research should consider primary and secondary data for a more comprehensive research on the topic. Pragmatic and more rigorous field work can be combined with the GIS modelling for more comprehensive and relevant flood risk decision-making purposes.
The authors would like to acknowledge all individuals who contributed directly and indirectly to R.A.A.’s work at the University of Johannesburg as a postdoctoral research fellow, which provided opportunity to write this research article.
The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.
R.A.A. contributed to all sections of this article except the GIS data processing and modelling sections, which were carried out by V.T.
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Data sharing is not applicable to this article as no new data were created or analysed in this study.
The analysis in this article is that of the authors and not necessarily that of their affiliated institutions.