1.1 BACKGROUND TO THE STUDY
In the past, heavy rainfall events have occurred to an increasing degree in Nigeria, some of which have even resulted in deaths. In addition to personal injury, this has also resulted in serious damage to property, particularly to physical infrastructure. The more frequent occurrence and rise in rainfall intensity of such weather events as well as the occurrence of extreme storms, hot spells or droughts is, according to the Nigeria Strategy for Adaption to Climate Change (NAS), a result of climate change. A problem we face in our time is that the structures of Nigeria cities that have grown fail to account for this development and corresponding measures to manage this have been neglected. Knowledge of the vulnerability of physical infrastructure as well as taking measures to protect existing buildings or so-called adapted building that takes the local situation into account as well as special building materials are becoming increasingly important. This report will present the vulnerabilities of the individual building materials and describe measures to protect physical infrastructure. Special attention will also be paid to available areas within the urban domain for binding and using heavy rainfall or allowing it to infiltrate or evaporate. Worldwide, there are an increasing number of strategies employing a so-called sponge city, which handles precipitation water in the city in a sustainable manner. A return to a more natural water regime in the city means that water will be retained in the area or in special reservoirs in order to use it e.g. for management of green space. Increased evaporation will also lead to a sustainable improvement in the microclimate as cities are cooled overall. At the same time, measures for creating a sponge city cannot only be evaluated and planned over longer time frames; rather they can also have a positive effect in the event of brief heavy rainfall events. The concept of the sponge city is primarily relevant with respect to long-term, higher-level urban planning as the measures generally concern public areas. It becomes all the more necessary to also break down these concepts to the smallest possible division within a city: a property. Therefore, the term "sponge property" will be introduced in this report. In addition to the protection of buildings, measures for the storage, infiltration as well as the evaporation and transpiration of a defined heavy rainfall event have been devised at the level of the property. In a computer-based calculation model, the effects of the individual measures were demonstrated on a sample property and then evaluated with the expected costs (cost-benefit analysis). The measures are evaluated considering various local aspects such as topography or soil conditions to allow for transferability. Rainfall pattern in Nigeria suggests that rainstorms are getting more intense. The data show that there are fewer rainy days, yet the total yearly amounts of rainfall have not changed much from previous decades. This means that more rain is falling on the days that there is rain, which in turn means that rain storms in the city are getting more intense, increasing the threat of flooding. In addition to more intense rain storms, the other possible cause of flooding in coastal regions is raising sea levels. Although up-to-date data on the rising sea levels in Nigeria are scarce, it’s believed that if nothing is done, this is likely to aggravate flooding in the future, particularly in coastal cities. Areas at risk include Lagos state, which is on the coast, as well as the Niger Delta region which has many low-lying towns and villages. Being on the coast also makes these places more susceptible to storm surges. While these areas are no stranger to floods, evidence suggests that floods have become increasingly common and intense in recent times. In the Northern parts of the country, heavy rains are likely to cause rivers to overflow their banks and cause flooding in the adjoining states. The changes in rainfall patterns, particularly in frequency and intensity, have meant that these events have begun to happen more frequently. In Nigeria’s cities, the most common cause of flooding after excessive rains is poor drainage systems that can’t cope. This is called pluvial flooding. Lagos provides a good case study. Lagos has been urbanising rapidly. By some estimates there will be 20 million in the city by 2050, making it the 11th most populous city in the world. It is also home to most of the country’s industrial, commercial and non-oil operations. Urbanisation and industrialisation increase the number of roads and buildings. This in turn increases the proportion of surface area where water cannot be absorbed into the ground, leading to rapid runoff which then causes flooding during storms. And in cities that manage their infrastructure well, storm water drainage systems are built so that water can be directed to rivers efficiently and quickly. Lagos has not kept up with its infrastructure needs. The growth and expansion of the city has been largely unregulated. This has resulted in inadequate and poor housing, the development of slum areas and inadequate water supply and waste disposal, among other problems. What’s complicated the situation for Lagos is that many parts of the city were originally low-lying mangrove swamps and wetlands, which have been reclaimed and settled, mostly by poorer communities and more recently through concerted efforts by the government. These low-lying areas are particularly at risk of flooding, and the situation is complicated by buildings being constructed on water ways, and bad waste dumping habits which block the drains. 70% of the population of Lagos live in slums, with the density of people being as much as 120,000 people per square kilometre.
1.2 STATEMENT OF PROBLEM
Incidents of heavy rainfall are not a recent phenomenon to people of Lagos state as they have been living in flood prone areas for centuries. Like most urban areas of the third world, Lagos state has experienced accelerated population growth which has led to changes in the land use activities. Land use changes in particular, have a direct impact on the magnitude and behaviour of floods (Civco et al 2011). Flash floods are common features in Nigeria during the rainy season(May-October) but the country’s flood event of the year 2012 have been described as the most devastating in over 40 years. Two major events took place between the months of September and October 2012 in Nigeria, namely the Ladgo Dam flood in Adamawa State, and the River Benue and Niger adjoining States floods (Niger and Benue States). The event pushed most of the country’s rivers over their banks and submerged hundreds of kilometres of urban and rural land. This resulted in widespread devastating flood disaster that hit the country cutting across major cities in about 14 states that borders the Niger-Benue River. The flood submerged houses and several transportation routes throughout the affected areas nationwide. Overall, an estimated 1.3 million people were displaced and about 431 people lost their lives with several hectares of farmland destroyed (MISNA, 2012). Though the unusually large flood was predicted by the Nigeria Metrological Agency NIMET, government at all tiers failed to act on time, resulting in the worst humanitarian crises in Nigeria since the civil war in 1967-1970. Despite the expected increase in frequency and magnitude of flood in the Nigeria and invariably Lagos state, few impact assessment studies on the socio-economic livelihood of the people have been undertaken to establish the underlying causes of their vulnerability. In the absence of comprehensive data and information, the measures to cope with flood have remained ad hoc.
1.3. AIMS OF THE STUDY
The major purpose of this study is to examine the effect of heavy rainfall in Lagos state. Other general objectives of the study are:
1. To examine the causes of heavy rainfall in Nigeria.
2. To examine the climatic changes in Nigeria.
3. To examine the effect of heavy rainfall in Lagos state.
4. To examine the consequences of heavy rainfall in Nigeria.
5. To examine the relationship between rainfall pattern and urbanization in Nigeria.
6. To investigate the adaption of mitigation strategies by Lagos state residents on the effect of heavy rainfall in Lagos state.
1.4 RESEARCH QUESTIONS
1. What are the causes of heavy rainfall in Nigeria?
2. How has the climate changed in Nigeria?
3. What are the effects of heavy rainfall in Lagos state?
4. What are the consequences of heavy rainfall in Nigeria?
5. What is the relationship between rainfall pattern and urbanization in Nigeria?
6. What are the adaptions of mitigation strategies by Lagos state residents on the effect of heavy rainfall in Lagos state?
1.5 RESEARCH HYPOTHESES
H0: There is no significant effect of heavy rainfall in Lagos state.
H1: There is a significant effect of heavy rainfall in Lagos state.
H0: There is no significant relationship between rainfall pattern and urbanization in Nigeria.
H1: There is a significant relationship between rainfall pattern and urbanization in Nigeria.
1.6 SIGNIFICANCE OF THE STUDY
The findings of this study will be beneficial to government, residents of Lagos community, farmers and other researchers. The study will provide information on the perceived extent to which heavy rainfall has impacted on the community. The knowledge of the findings would help the government to make policies on how to check the effects of heavy rainfall on urban areas and Nigeria in general. The study will provide information to Lagos state residents on adaptation strategies, which they could adapt to in such situations. The study could be used as a resource material on heavy rainfall and its impact on Lagos state for researchers who may be interested in researching on related topics.
1.7 SCOPE OF THE STUDY
The study is based on the effect of heavy rainfall in Lagos state, a case study of Orile Agege.
1.8 LIMITATION OF STUDY
Financial constraint- Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).
Time constraint- The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.
1.9 DEFINITION OF TERMS
Climate Change: The Intergovernmental Panel on Climate Change (IPCC) defines climate change as a change in the state of the climate that can be identified by changes in the mean and / or the variability of its properties and that persists for an extended period, typically decades or longer.
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