Climate change is an adverse environmental phenomenon that is causing enormous concern all over the world. In this article we look at the adverse effects of climate change on Nigerian Built Environment.
Climate change refers to some anomalies in the climate system that is a result of human activities. These anomalies include increase in the concentration of Greenhouse gases (GHGs), Hydro-fluorocarbons (HFCs) and Chlorofluorocarbons (CFCs) in earth’s atmosphere, which will ultimately lead to global warming.
In fact, global warming has already begun, as earth’s temperature has risen between 0.4 and 0.8°C in the last 100 years.
Nigeria is one of the world’s most densely populated countries with a population of over 180 million people, half of which are considered to be in abject poverty. Nigeria is recognized as being vulnerable to climate change.
As the key climate change indicators such as increasing temperature and intensity of rainfall are being verified in Nigeria, the consequent impacts of climate change connected to these symptoms are to be expected in Nigeria.
With the increasing incidence of climate change related hazards and disasters, considerable damage to buildings and infrastructure is expected. Lagos being one of the largest/fastest growing cities in the world and the foremost manufacturing port city in West African sub region is not left out of the climate change brouhaha and may probably be worst hit by its effect in relation to the West African Region.
Its importance as the economic hub of Nigeria, its coastal position, the peculiarity of building development makes it an ideal case study of the impact of global climate change on Nigerian built environment.
At present, roughly 50 percent of the world‘s population live in cities, but this figure is expected to rise over the years. Most of the future growth of the urban population is anticipated in the developing world.
Many low-income countries are already exposed to shortages of clean drinking water and poor sanitation, and often occupy high-risk areas such as floodplains and coastal zones. As the concentration of urban populations is increasingly mixed up with growing risks of extreme events, millions of naira is lost and the cost is increasing by the day.
The significant contribution made by the world‘s major cities to global climate change and the urgent need for energy efficient infrastructure and changed patterns of resource consumption is notable. With such a range of issues to tackle, it is not surprising that there have been calls for wider participation and more effective interaction between complementary disciplines.
Climate change will increase the frequency and intensity of heavy rainfall events, thereby increasing the risk of urban flooding. While addressing infrastructure issues is a necessary component of reducing urban flood risk, individual homeowners can have a significant role in reducing risk through protecting their own homes and reducing their contributions of storm water to municipal sanitary sewers and storm water management systems.
However, the barriers of low public awareness will have to be overcome to effectively engage homeowners in urban flood risk reduction. Some cities have been working to improve homeowner knowledge and risk-reducing behaviour through education and financial assistance programs in the advance world
Urban flooding occurs in urban areas, where the impacts of extreme rainfall are exacerbated by high concentrations of impervious surface, infrastructure, buildings, property and people. Urban flooding can have serious implications for both buildings and infrastructure, as extreme flows of water during heavy rainfall events can damage both overland and underground storm-water management infrastructure and road pavements.
Flooding has also become the greatest reasons for the numerous gully erosion problems because of concentration and discharge to many unsafe areas. These are mainly due to poor road designs, numerous public and private building springing up and exposing land surface in many built up areas
Under a changing climate, an increase in the frequency of drought, extreme rainfall, high temperatures, wind events is expected and we can expect an exacerbation of the health impacts associated with these events.
It has been argued that extreme events that currently have return frequencies of 1 in 100 years could have return frequencies of 1 in 5 or 1 in 10 years by prevailing climate change conditions.
As temperatures increase, evaporation will also increase and the atmosphere will be able to hold more moisture. Higher amounts of moisture in the atmosphere will result in more severe precipitation.
Although the precise impacts of climate change will differ depending on the climatic and environmental characteristics of specific regions, it is often thought that extreme precipitation events could increase in severity by approximately 15 percent.
Increasing frequencies of extreme rainfall events caused by climate change will mean that storm-water management infrastructure design standards will be less reflective of the frequency and intensity of events that we will experience in the future.
Understanding public perceptions of natural hazards is an important part of non-structural hazard management. In comparison to structural approaches to hazard management, which attempt to alter the hazard to reduce risks to population (e.g., building dams and levees to control flooding), non-structural approaches attempt to alter human behaviour to reduce vulnerability.
A commonly applied non-structural measure may be the use of floodplain maps to steer development away from flood prone areas. Non-structural measures also include education programs and actions designed to increase the awareness and risk reducing actions of the individuals who are exposed to hazard risk.
People who live in areas subject to hazards are largely unaware that they could sustain damages, personal injury, or death. In most cases, less than half are aware of their exposure to natural hazards.
Also, people who live in hazard prone areas rarely take actions to protect themselves. Many studies have revealed that less than 15 percent of individuals exposed to hazards take actions to reduce their risk of sustaining damages.
When people do take action, they generally take inexpensive and less effective actions such as evacuating at the last minute, or moving valuable items to a higher level in their home during a flood event.
Perception studies have frequently revealed that people with property prone to flooding rely highly on government built structural mitigation mechanisms, such as dams, levees and floodwalls, to protect them from damages.
Studies have also revealed a high reliance on government for flood protection, and that often the blame for damages caused by natural hazards is placed on government rather than extreme natural events or on those who choose to occupy hazard prone areas.
Homeowners are more likely to attribute responsibility to their municipalities than to take action themselves to reduce urban flood risk. Those findings have serious implications for how hazards are managed, specifically highlighting the importance of public awareness through effective hazard education.
We can’t shy away from the fact that human activities will continue to change the composition of the atmosphere and global mean temperatures and sea levels will continue to rise for many centuries to come.
The risk of a heat wave like that experienced across Europe in 2003 is thought to have doubled due to historic greenhouse gas emissions. However, the range of potential impacts is expected to go beyond heat waves.
Other anticipated consequences of climate change for Nigerian cities include fewer periods of extreme cold; increased frequency of air and water pollution, rising and changes in the timing, frequency and severity of urban flooding associated with it.
Detection of climate driven trends at the scale of individual cities is problematic due to the high inter-annual variability of local weather and factors such as land-use change or urbanization effects. It has long been recognized that built areas can have urban heat island (UHI) that may be up to 5-6 degrees celsuis warmer than surrounding countryside.
Compared with vegetated surfaces, building materials retain more solar energy during the day, and have lower rates of radiant cooling during the night. Urban areas also have lower wind speeds, less convective heat losses and evapotranspiration, yielding more energy for surface warming.
Artificial space heating, air conditioning, transportation, cooking and industrial processes introduce additional sources of heat into the urban environment causing distinct weekly cycles in UHI intensity.
The physical constituents of built areas and human activities within urban centres also interact with other climate drivers. For example, run-off from impervious surfaces can have dramatic effects on downstream risks of flooding and erosion, as well as water quality via uncontrolled discharges of storm water.
Urban air pollution concentrations may also increase during heat waves with significant consequences for mortality. This is because high temperatures and solar radiation stimulate the production of photo-chemicals among as well as ozone precursor biogenic volatile organic compounds (VOCs) by some plants.
Potential climate change impacts of built environment in Nigeria Flooding
* More frequent and intense rainfalls leading to flooding and overwhelming of urban drainage systems.
* Heightened water demand in hot, dry times
* Reduced soil moisture and groundwater replenishment.
* Poorer air quality affects asthmatics and causes damage to plants and buildings.
* Higher mortality rates in Nov. – June due to heat stress.
* Increased competition from exotic species, spread of disease and pests, affecting both fauna and flora.
* Increased ground movement in affecting underground pipes and cables.
* Reduced comfort and productivity of workers.
* Increased disruption to transport systems by extreme weather.
* Reduction in cold weather-related disruption.
Assessing urban flood risk is further complicated by the performance of the urban drainage system, which responds to highly localized effects such as blocked culverts or overwhelming of the hydraulic capacity of sewers.
There is also a wide variety of tangible and non-tangible secondary impacts associated with flooding in urban areas. Urban litters and blockages remain major problems in Nigeria.
In Nigeria, reports estimate that many urban properties are presently at risk from flooding caused by heavy downpours, yielding average annual damages of billions of Naira.
However, the authors concede that considerable uncertainty surrounds the incidence of flooding because of the complex interplay between the amount of precipitation change in relation to the excess capacity of drain and drainage pipes and it is also difficult to quantify other costs associated with water flooding, or risks to human health such as diarrhea and respiratory diseases.
There could also be significant disruption to system-wide performance of transportation networks all over the urban areas.
There is no doubt that the populations, infrastructure and ecology of cities are at risk from the impacts of climate change. However, tools are becoming available for addressing some of the worst effects.
For example, appropriate building design and climate sensitive planning, avoidance of high-risk areas through more stringent development control, incorporation of climate change allowances in engineering standards applied to flood defences and water supply systems, shoreline protection works.
Citizens also have a responsibility to mitigate their collective impact on the local and global environment through reduced resource consumption and changed behaviour.
This review has described the most significant climate change impacts expected to shape the future character and functioning of urban systems, in Nigeria. Several important knowledge gaps have emerged.
First, there is an ongoing need to improve preparedness and forecasting of climatic hazards, such as intense heat island or air pollution episodes, to safeguard human comfort and health in Nigeria.
Second, there is clearly a need for improved representation of intra-urban flooding, at local, city and catchment scales.
New modelling techniques will also be needed to exploit fully emergent probabilistic climate change information. But there could be new cost implications arising from the use of such data, dependent on the level of risk and uncertainty that is acceptable in the resultant engineering design.
This has been done successfully in years 2012 and 2013 by NIMET in Nigeria.