Recent flood incidents in Nigeria have overprinted their rhythms in terms of recurrence time and intensity. In this article, we examine the pattern of flood incidences across Nigeria and distributions across the six geo-political zones of the country. Furthermore, we discuss some of the major causes and effects of flooding in the Nigeria.
Nigeria is located in West Africa with an area of 923 768 km2 of which 910 768 km2 is made up of land and 130 00 km2 is coastal area.
The seasons and patterns of rainfall vary across the country, which have also affected the cover distribution. The coastal/southern area has the highest rainfall ranging from 1500 and 4000 mm, while the mid-belt and the extreme north have rainfall ranging from 600 to 1400 mm. High temperature and humidity as well as marked wet and dry seasons characterizes the Nigerian climate.
The vegetation of Nigeria is also diverse from mangrove/high forest in the south to savannah in the mid-belt and grassland in the extreme north. Also diverse is the vegetal cover density across the country. The population of the country stands at about 190 million people with majority depending on agriculture directly or indirectly for survival both in the rural and urban centres.
Flood incidence in Nigeria seems to affect all the geopolitical zones, although with different intensities. Furthermore, flood incidence concentrate more along states that border the major rivers; i.e. SS and SE which are situated at the lower end of the River Niger and the delta from where water is discharged to the Atlantic Ocean.
Usually, the month of September records the highest flood event (50 percent of total occurrences) across the six geopolitical zones. It was followed by August, October, and July.
While most parts of the country are affected by the flood, the southern axis of the country suffers most, with the highest intensity recorded in the Niger delta region (SS and SE).
Several factors interact to cause the recent yearly severe flooding in Nigeria.
The level of infrastructural development within Nigerian urban settlements has increased the level of concretization and asphalting of the land-surface leading to enhanced runoff from rainfall while diminishing the infiltration rate of the soil. The implication is that more water from rainfall is available on the surface of the earth to run as surface flow which we call flood.
Concomitantly, the infiltration capacity of the soil is reduced due to the preponderance of urban infrastructure such as buildings, asphalted roads, concrete car parks and other paved surfaces. Flooding can be worsened by increased amounts of impervious surface, which reduce the supply of vegetation that can absorb rainfall.
Moreover, recent surge in urbanization in Nigeria has seen people building in places that are clearly flood reception zones or flood prone areas. Such enterprise that involves the erection of structures on flood plains will naturally suffer at the slightest sign of flooding.
When construction infringes on a drainage channel, then the water will move elsewhere if it cannot uproot the obstruction on its path.
Climate change which is associated with global warming has created significant distortions to the local climate pattern in Nigeria.
For instance, intense afternoon thunderstorms that can generate over 200 millimeters of rain within a day or even shorter duration have become commonplace because global warming has provided the needed thermal energy for increased evaporation along the Atlantic Gulf of Guinea. A combination of enhanced thermal and activities, therefore drive the massive rainfall regime that coastal locations in Nigeria have been experiencing lately.
For instance, many coastal towns in Nigeria such as Lagos, Ibadan and Calabar, Eket, have received excessive rainfalls recently which resulted in historic floods that caused substantial loss of lives and property. Climate Change is an attributed cause of flooding because when the climate is warmer it results to heavy rains, and rise in sea level.
Contrary to popular wisdom, climate change or unusually high rainfall is not the primary cause of flooding problem in some cities across Nigeria especially Lagos. Rather, the increased urbanization, lax planning laws in relation to the city are to blame. A lasting solution to flooding problems will require the incorporation of sustainable drainage system within the existing flood management strategy for the city and planning.
Other causes of flooding in Nigeria include the following:
4. Unusual high tide, failure of dams, levees, retention ponds, or other structures that retained the water
5. Runoff from sustained rainfall exceeding the capacity of a river’s channel
6. Unexpected drainage obstructions such as landslides, or debris can cause slow flooding upstream of the obstruction
7. Unusual High Tides: Coastal areas are sometimes flooded by unusually high tides, such as spring tides, especially when compounded by high winds and storm surges.
Flooding has done various degree of physical damage to structures, such as bridges, cars, buildings, sewerage systems, roadways and canals.
Extreme cases flooding in Nigeria has caused loss of lives. At least 102 people are now thought to have been killed by floods in and around the south-western Nigerian city of Ibadan.
Part of the built environment are often damaged or destroyed as a result of flooding with high repair costs and long periods required for reinstatement.
Vital infrastructure were also damaged or disrupted. For instance, electricity and gas supplies were interrupted to individual properties but also to wider communities in cases where sub stations and transformers themselves were flooded. Road links, railways, canals etc., were blocked causing disruption to the wider transport network and accessibility severely disrupted for local inhabitants, especially amongst those considered most vulnerable.
The loss of electricity as a result of floods resulted in the loss of communications networks. Telephones, radios, televisions and the internet are all increasingly reliant upon mains power.
Floods took a deadly toll in northeastern Nigeria in August 2011. Torrential rains pushed rivers over their banks, collapsed mud houses and washed away livestock. Floodwater, resulting from heavy rains, damaged bridges and caused a dam to overflow, submerging buildings across the city. Most of the victims were children.
The social and emotional costs from flooding can also be significant and are often widespread. These costs include: displacement from homes, the loss of personal valuables and the ongoing fear and insecurity caused by the experience. Potable water supplies may be lost or contaminated in a flood and this can have immediate health effects upon people and animals.
The economy of affected areas had been severely affected by flooding. Businesses lost stock, patronage, and productivity and disruption to utilities and transport infrastructure crippled activities in affected areas.
Tourism, farming and livestock can equally be affected.
Nigerians have to avoid dumping refuse or solid materials in drains.
1. There is need to keep our gutters and drains always clean.
2. There is need for government to issue and strictly enforce regulations banning building and residing in flood prone zones or areas. Furthermore, there is need for government to build and develop infrastructure which will prevent or limit floods and protect the population.
3. There is need to remove or demolish all structures obstructing drainage that can obstruct free flow of water.
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