Many cities rural settlements across Nigeria face growing problems of severe flooding due to increased storm frequency and intensity related to climate change. In this article, we take a look at the impact of climate change on flooding in Nigeria. We conclude that although climate change worsens flooding in Nigeria, local factors such as the growing occupation of floodplains, increased runoff from hard surfaces, inadequate waste management and silted-up drainage also contribute to the problem. From the foregoing, there is the need for the Nigerian government and to act to alleviate flooding and its causes, especially the consequences of climate change.
Climate change is a vital environmental factor that shape and re-shape various activities of human beings in a society.
According to the United Nations Framework Convention on Climate Change (UNFCCC), climate change can be defined as a change of climate which is attributable directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over a comparable time periods.
Causes of Climate Change: Human factors (industrialization, technology development, urbanization, deforestation and burning fossil etc) and natural factors (solar radiation quality and quantity, astronomical position of the earth) are notable causes of climate change.
Nigeria is located on the coast of West Africa and has a total landmass of about 925,796 square kilometer.
The climate of Nigeria varies more than those of any other country in West Africa, because of its great length from south to the north, which covers all the climatic belts of West Africa.
Nigerian climate is humid in the south (with annual rainfall over 2,000 mm/year) and semi-arid in the north (with annual rainfall approximately 450 mm/year). Rainfall commences
around March/April from the coast (in the south), spreads through the middle belt between April and May, to eventually get to the northernmost part between May and June.
Nigeria can be divided into three climatic zones: Guinea, Savana, and the Sahel. The country can also be grouped into seven ecological zones, ranging from south to north of the country, namely: Mangrove, Fresh water swamp, Rainforest, Woodland or tall grass savanna, Montane, Short grass savanna, and Marginal savanna. The Mangrove, Fresh water swamp and Rain forest zones roughly are in Guinea zone; Tall grass and Montane zones are in Savanna zone, while Short grass savanna and Marginal savanna are in Sahel zones.
Flooding is a natural phenomenon that refers to unusually high rates of discharging; often leading to inundation of land adjacent to streams, and it is usually caused by intense or prolonged rainfall.
The occurrence of flood represents a major risk to riversides populations and floodplains, in addition to causing substantial impacts on the environment, including aquatic plants and animals, and bank erosion.
Flooding is often worsened by human activities such as the presence of riverside infrastructure (dams, piers, and lands); and by poor development practice including riverside development, excessive cleaning, encroachment upon water ways, dredging which may cause changes in the hydrological balance of water-ways involved.
Floods occur in Nigeria in three main forms, namely; coastal flooding, river flooding and urban flooding. Coastal flooding occurs in the low-lying belt of mangrove and fresh water swamps along the coast. River flooding occurs in the floodplains of the larger rivers, while sudden, short-lived flash floods are associated with rivers in the inland areas where sudden heavy rains can change them into destructive torrents within a short period. Urban flooding on the other hand occurs in towns, on flat or low-lying terrain especially where little or no provision has been made for surface drainage, or where existing drainage has been blocked with municipal waste, refuse and eroded soil sediments.
Frequent occurrence of floods can be attributed to the impositions made by cities on their environment. In some cases, natural ecosystems are often destroyed owing to demand for renewable resources, such as water, fossil fuels, land and building materials (development). Also, human influences in urban areas have considerably altered the hydrological system and nature of the ground surface causing destructive flood disaster and its attendant physical and socioeconomic outcomes (e.g. disruption of socioeconomic activities, loss of properties, inaccessibility and reduction of the aesthetic quality of the environment).
Flooding often arises as a result of the extension of urban areas unaccompanied by development of strong drainage systems, adequate planning and disaster management strategies. Indeed, flooding is one of the most devastating hazards that are likely to increase in many regions of the world partly due to global climate change and poor governance.
The heavy rainfall coupled with bad human activities in relation to the environment and lack of drainage infrastructure in most Nigerian cities has left hundreds of people distressed and homeless. It should be mentioned that flooding in cities can contaminate water supplies and intensify the spread of epidemics diseases, diarrhea, typhoid, scabies, cholera, malaria, dysentery and other water-borne diseases.
Increasing temperature (global warming) and decreasing rainfall in most parts of the world are the greatest impacts of climate change.
The increasing temperature has led to increased land-based ice melting. The thawing of the Arctic, cool and cold temperate ice, the increasing rainfall in some parts of the world and expansion of the oceans as water warms has started impacting on sea level rise, coastal inundation and erosion.
The implication is that the present 0.2 m sea level rise has inundated more than 3, 000 kilometer square of the coastal region of Nigeria, and if the sea level rise continues unchecked, more areas in the coastal region will be flooded. Coastal settlements like Bonny, Eket, Forcados, Lagos, PortHarcourt, Warri and Calabar among others that are less than 10 m above the sea-level would be seriously threatened by a metre rise of sea-level.
The worst impact is population displacement, which may result in communal crisis. The coastal inundation and erosion with their associated population displacement are currently major environmental problems in Nembe, Eket and other coastal settlements in Bayelsa, Delta, Cross River, Rivers, and Lagos States of Nigeria.
It is estimated that a metre rise in sea level will displace about 14 million people from the coastal areas of Nigeria. The worst impact is population displacement, which may result in communal crisis. The coastal inundation and erosion with their associated population displacement are currently major environmental problems in Nembe, Eket and other coastal settlements in Bayelsa, Delta, Cross River, Rivers, and Lagos States of Nigeria. It is estimated that a metre rise in sea level will displace about 14 million people from the coastal areas of Nigeria.
Climate change is making weather less predictable, especially in third world countries like Nigeria where facilities to predict and manage weather conditions are inadequate. Climate change worsens urban flooding by altering the pattern of flooding in the flood prone areas.
Without doubt, climate change and its impacts such as increase in sea level have direct impact on urban and coastal floods, and it continuously disrupts the social fabric of cities and worsens poverty in the country.
However, urban flooding is not just related to heavy rainfall or extreme climatic events; it is also related to changes in the built up areas themselves. Abuse of urban land through development is a major factor that influences the incidence of flooding in urban areas.
Despite the knowledge of climate change and its impacts especially in urban environment, it is sad to note that, most Nigerian cities find it difficult to provide in advance resilient and adaptation measures that will cater for the hazards such as increased floods resulting from global climate change. Meanwhile, adaptation within the realm of climate change include actions taken by people in response to, or in anticipation of changing climate conditions in order to reduce adverse impacts or take advantage of any opportunities that may arise.
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