Globally, floods remain among the most common and dangerous disasters that do not only displace and kill people but also destroy livelihoods, personal properties, and public infrastructure [1
]. Floods often affect victims’ mental health and disrupt the social functioning of communities [4
]. However, research has shown that the devastating impact of floods can be reduced through the application of proactive technology [5
Modern technological applications, notably remote sensing (RS) and geographic information system (GIS), together known as geospatial techniques, are emerging as effective methods for preventing flood hazards [5
]. In contemporary societies, for instance, geospatial techniques can be used for mapping areas of flood hazard and for predicting flood occurrences [2
]. Accurate prediction of areas of flood hazard remains an important priority in flood risk reduction initiatives [9
]. Even before a flood disaster strikes, it behooves authorities to have readily available maps detailing hazardous zones [10
]. When authorities correctly map flood hazard areas, it facilitates not only the timely rescue of potential victims from the flood-related crisis but also prevents post-crisis difficulties, such as issues related to insurance claims [11
]. Several studies, including the works of Aja et al., Asare–Kyei et al., Baishya and Sahariah, Danumah et al., and Elkhrachy [7
] have argued for the use of geospatial techniques in mapping areas of flood hazards. The Sendai UN Conference on Disaster Risk Reduction in 2015 also highlights the importance of using geospatial techniques by states/local actors to implement programs designed to prevent and reduce disasters and their consequences [16
Many sub–Saharan African countries are highly susceptible to floods [18
]. Ghana, Nigeria, Burkina Faso, Cote d’Ivoire, and Senegal continue to experience flood problems annually [13
]. In 2012, for instance, three million homes in Nigeria were inundated by floodwaters, and an estimated 1.4 million people were displaced [20
]. In 2013, flood disasters in the sub-region led to the death of 84 people, displaced 40,445, and destroyed about 34,000 hectares of farmlands [20
]. It is important to note that even dry areas in West Africa are not spared by floods as flood disasters displaced 27,289 people in Niger (a drought-prone country), between 1970 and 2000 [21
]. Factors that have accounted for flood cases in the sub-region include erratic rainfall patterns, geographic location, and low elevations [13
Developing nations mostly have constraints with access to high-quality data for effective flood hazard monitoring [22
]. In West African countries, many districts do not have flood hazard maps [11
]. With a few exceptions, the available flood hazard maps are not updated periodically. Consequently, local state agencies mandated to manage floods resort to obsolete and less-effective methods, such as measuring watermarks on structures, ground surveys, aerial observations, and media reports [12
]. Such measures are insufficient as there could be the creation of new flood hazard areas [23
]. This may come at a high cost and can be labor-intensive when floods cover large areas [12
Ghana is among the countries in West Africa affected by devastating floods [19
]. The cost of damage due to floods in Ghana between 1990 and 2014 amounted to over USD 780 million [24
]. Floods were ranked as the second most fatal disaster type after epidemics in Ghana [24
]. In 2015, for instance, more than 150 people died because of a combined flood and fire disaster in Accra [25
]. While the majority of flood cases in Ghana often occur in cities, some towns and villages have also had difficult experiences with floods. The year 2010 saw over 2300 people displaced at Swedru in the Agona West Municipality due to flooding [26
]. The Upper East Region in October 2019 recorded flood disasters that claimed the lives of 19 people and forced over 26,000 residents out of their homes when over 5000 dwellings were affected [27
In the Cape Coast Metropolis (CCM), which is widely recognized as a major tourism and education hub in the country, flooding is a serious problem that keeps escalating because the area continues to attract many migrants coupled with heavy annual rains [28
]. In June 2016, a continuous heavy rainfall over ten days claimed ten lives. This reoccurred within the metropolis in 2019 [29
]. Studies have shown that the common causes of floods in Ghana result from natural factors (e.g., rainfall) and anthropogenic factors (e.g., poor physical planning, improper waste disposal system, and lack of or poorly designed drainage systems) [24
]. Annual flood events in Ghana aside from their toll on human lives, socio-economic activities, and the environment, tend to affect the government’s overall budget as the government invests a lot of money into relief operations whenever scores of people are affected [31
Although flood problems continue to escalate in Ghana, particularly in the CCM, most empirical studies aimed at helping to address the problem have focused on the national capital, Accra, and little has been done on the assessment and mapping of the flood problem using geospatial techniques [8
]. Using a modified flood index approach to mapping flood hotspots in CCM, this study seeks to exemplify and justify the importance of using geospatial techniques in addressing flood problems in Ghana and West Africa as a whole. The findings in this study have the potential of being a valuable reference document for flood control authorities and experts in the fight against flooding in the Cape Coast Metropolis and Ghana as a whole.
Based on geospatial techniques, this study mapped flood hotspots within the Cape Coast Metropolis (CCM) using an index-based approach. To the best of our knowledge, this is the first study to employ an index-based approach to mapping flood hotspots for the study area. The finding that the midsection of the metropolis down to the coastal areas was within medium and high flood hazard zones should be a great concern for both flood management institutions and residents of the CCM. As many communities within the high flood intensity areas were located close to streams as observed in Kwapro, Ankaful, Amamoma, and Duakor (please see Figure 6
), much consideration should be given to the relocation of residents close to these streams or building a defense block to prevent flood disaster in the future. Our suggestion corresponds with conclusions in some previous studies indicating that high flood risk zones are usually close to river bodies [11
] and that relocation of residents can be a life–saving opportunity for people living in such high flood hazard areas [4
Additionally, the dredging of streams can be an effective way of reducing flood hazards in the CCM as in the case of 2016 where concerned authorities sponsored the dredging of the Kakum River at Kwapro, leading to reducing flood cases in Kwapro (Figure 7
The findings from this study further suggest that flood hazards in the CCM result from the interplay of several factors: elevation, slope, flow accumulation, stream density, and distance from streams; Normalized Difference Vegetation Index (NDVI
), soil drainage capacity, and Land use/Land cover (LULC
). Areas with low elevation, small slopes, high stream density, low NDVI
values, and near the highest flow accumulation were found to be the main hotspots for flooding and vice versa, and these findings confirm the conclusions in previous studies elsewhere [6
Additionally, distance to stream networks played a crucial role in the flood hazard index; many of the communities classified under high flood territories were within a 500 m buffer of river bodies. This finding corresponds with the assumption that distance from river channels plays a critical role in flood inundation; therefore, river overflows should be considered since most rivers overflow their banks when water exceeds the carrying capacity of the river channel [40
In line with the findings of Nyarko [23
], land use played a contributory role in flooding in the Cape Coast Metropolis (CCM), and authorities in the CCM need to discourage deforestation and promote afforestation among residents of the locality. Moreover, it will be prudent for the authorities within CCM to devise strategies to protect wetlands from further encroachment as the resulting flood hazard map showed that most of the wetlands in the CCM are inhabited by people.
4.1. Policy Recommendations
Based on our findings, some recommendations are provided:
The Cape Coast Metropolitan Assembly (CCMA) should fund the dredging of rivers and streams as shown in Figure 7
every two years because the periodic dredging of river networks could salvage the situation. This would require huge financial allocation from the local assembly but would go a long way to reduce flood cases in the Metropolis.
Considering the role of vegetation in reducing runoff, it will be prudent on the part of city authorities to plant trees along riverbanks to serve as a buffer. This should be done with the total participation of the local folks since their involvement would prove crucial in ensuring success.
NADMO, CCMA, and Ghana Police should work in tandem to ensure strict compliance with buffer zone policies. Authorities must enforce such laws devoid of political interference or favor to deter residents from building close to riverbanks as shown in Figure 6
The Assembly should make the necessary effort to construct concrete banks to prevent sediments from filling the river channel.
Residents within the CCM especially those living in flood hazard zones should take education and early warning communication by disaster management organizations seriously to minimize the effects of floods should they occur.
Moreover, residents in CCM should construct houses with recourse to building codes since many communities lay within high flood hazard zones.
4.2. Limitations of the Study
Although this study demonstrates novel contributions to the mapping of flood hazards using geospatial technology, some limitations should be noted. Firstly, the study excluded direct rainfall from the factors responsible for flooding. This also comes at the backdrop that the CCM has a fairly good drainage capacity as shown in our findings—the soils in CCM allow water to percolate and did not influence high runoff. Secondly, we did not capture the spilling of excess water from the Brimsu dam in the metropolis. Excess water from this dam is commonly spilled over when the dam reaches its peak capacity. This exercise is intended to protect the dam from collapse but ends up increasing flood risk in the neighboring communities, such as Ankaful. The spilling of the water was not included in the list as this is usually a sponsored venture and the quantification of the amount of water spilled is difficult to measure.
Our study explored the use of remote sensing and GIS in mapping flood hotspots within the Cape Coast Metropolis (CCM) using an index-based approach. The study has contributed to the knowledge that simple mapping techniques can be used to determine flood hotspots in areas where data and expertise are major concerns. This study has identified that elevation, slope, flow accumulation, stream density, NDVI, distance from streams, and LULC are key contributory factors to floods in the CCM, and preventive measures can be focused on these factors. It is also worth noting that based on our method, the soil in CCM has been found as a less contributory factor to flooding in the CCM.
To prevent future flood disasters, however, authorities and residents of the CCM can utilize the new findings based on our flood hazard map for the effective planning of the metropolis. We believe that the suggested recommendations if carefully implemented would save lives, properties, and historical monuments in the CCM. The findings and approach used in this study can also be useful for future studies aimed at mapping other flood hazard areas in Ghana and even beyond.