Megacities are metropolitan areas, which have populations of more than ten million people. Cities, which also have a population density of more than two thousand persons per square kilometre, are described as megacities. They can also either be single metropolitan areas or combinations of two or three metropolitans. Megacities are spread throughout the world, with Asia harbouring the majority of them. In the year 2011, there were twenty one existing megacities. The number of megacities has increased from only two in the year 1950 to four in 1975, twenty one in 2003 and twenty seven in 2011. Among all this cities, two thirds of them are located in the developing countries of South East Asia (Brockerhoff and Brennan 1998).
The origin of the megacities dated back in the early 1800s, when Rome was a megacity. Its large population was the result of its political importance and the economic stability. Other megacities such as Baghdad and Shanghai also existed in the early years. The emergence of these megacities has increased in proportion to the population of the world increase. Today, the most common megacities in the world include Shanghai, Tokyo, Delhi, Mumbai, Jakarta and Mexico City.
The high rate of population growth influences the increase of the number of megacities. With the highest growth rates being among the third world countries of Africa and Asia, most of the megacities are also located there. This large urban population is usually influenced by the continuous rural to urban migrations witnessed in most countries. These rural to urban migrations are steered by the progress in nutrition, agriculture and medicine in the urban areas. They are also influenced by factors such as the modern lifestyle in the urban areas, economic opportunities and the attractive jobs. These factors have caused people to relocate to the urban areas, causing the continued increase in the number of megacities (Aguilar & Escamilla 1999).
The growth of megacities has led to the emergence of both social and environmental challenges. These challenges have brought negative effects to the inhabitants of these cities and also to the natural environment in the surrounding cities. The mother of all this problems is overpopulation. The number of inhabitants living in the cities of Jakarta, Dhaka, Delhi and Karachi tripled between the year 1975 and 2003. Mexico, for example, has a population of twenty million inhabitants living in 1,485 square kilometres. This indicates a population density of about thirteen thousand, four hundred and seventy inhabitants per square kilometres. In Shanghai, the largest city in the People’s Republic of China, more than twenty five million people live in 6,340 square kilometres of land. Other highly populated megacities include Dhaka, Lagos in Nigeria, Sao Paulo, and Cairo. This high population, followed by a high rate of population growth, has caused numerous challenges for urban policies and the urban planning strategies (Stein 1992).
The high population of people in these cities produces adverse social effects on the inhabitants of the megacities. The number of people in these cities is way beyond the city’s carrying capacity. This means that the ratio of available resources to the number of inhabitants in these cities is not balanced. Megacities are deficient of parameters which are used to evaluate whether a city is overpopulated. Such parameters include clean water, shelter, clean air, food and other life sustaining resources. This high population also causes problems of medical care, sewage treatment, energy supply, education and waste disposal.
Megacities experience many risks and are vulnerable to both manmade and natural disasters. This is because most of these cities are concentrated in areas, which are prone to disasters such as earthquakes, floods and landslides. Mexico City, for instance, sits in a valley. It is located in a place that was once a lake making it vulnerable to flooding. Some of the manmade disasters such as accidental fire are also common in these cities. These natural and manmade disasters cause massive losses of property and people’s lives due to the high population density of these cities.
There is a shortage in some basic necessities, such as fresh water, in these overpopulated cities. Fresh water is essential for use as drinking water and treatment of sewage and other effluents. In Mexico City, millions of inhabitants live in the slums, and they lack access to fresh water. The large volume of water getting into the city is highly polluted. Many of the city’s freshwater streams and rivers act as waste removal canals. This presents a health hazard to the inhabitants of the city. They are exposed to risks of acquiring water borne diseases such as cholera and bilharziasis (Brockerhoff and Brennan 1998).
The poor water infrastructure put in place also hinders the availability of fresh water. The inhabitants of this city tamper with the water distribution gadgets so as to escape paying the water charges. They do this by putting up illegal water connections that are both hazardous and unhygienic. The available fresh water in the underground aquifers is also threatened by the excessive pollution in the city. The contaminated water from the poor sanitation and the industrial wastes leads to many diseases and health problems (United Nation 1998).
The other negative effect of the megacities is the increase in the levels of water pollution, air pollution, noise pollution and soil contamination. The level of pollution in the megacities is increasing at alarming rates. This pollution directly threatens the health of many individuals including those, who do not reside in these cities. There is an increase in the air pollution due to the gases emitted by the large number of automobiles and industrial objects in these cities. Combustion of fossil fuels produces the largest amount of the pollutant gases. The motor traffic is the main source of air pollution in the megacities. The main modes of transport in there are railways and private vehicles. These two transport methods produce many harmful gases into the atmosphere (Stein 1992).
There is a strong relationship between the levels of air pollution and the health of individuals. Air pollution causes both long-term and short-term effects depending on the exposure of an individual. An exposure to high levels of air pollution leads to acute respiratory problems. Some components of the polluting gases are also known to be carcinogenic. The polycyclic aromatic hydrocarbons, for instance, accumulate slowly in the bodies of the megacity dwellers and produce long-term cancerous effects. The children are exposed to higher risks of getting cancer because of their relatively smaller body size (Aguilar & Escamilla 1999).
The pollution caused by gases from these cities also reduces the amount of ultraviolet light reaching the earth. These gases accumulate in the atmosphere and reduce the penetration of sunlight into the earth. The reduced amount of ultraviolet light favours the growth and proliferation of harmful viruses and bacteria that are killed normally by ultraviolet light. The increased emission of harmful pollutants into the environment, such as pollutant matter and nitrogen oxides, influences the quality of air and affects climate changes. Climatic changes are not only affected at a regional level but also continentally and globally. These emissions also affect the existence of significant agricultural and natural ecosystems in the regions, which surround the megacities. They influence the atmospheric chemistry of that region, and also alter the climate change of the whole globe. In India, more than thirty percent of people, adding up to more than three hundred million people, live in the megacities. These people are now being faced with the challenge of dealing and living with polluted air.
The world health organization ranked eighteen megacities in terms of air quality. Five out of the eighteen were ranked as fair while the remaining thirteen were ranked as poor. In terms of TSP, Karachi was ranked as the most polluted megacity. When judged according to the MPI values, Dhaka was ranked as the most polluted city. It was also ranked as the fourth most polluted city in terms of the ambient air concentration of sulphur dioxide and nitrogen dioxide. This indicated that the air pollution levels in the megacities were significantly high. World Health Organisation reported that seven megacities including Beijing, Mexico city, Jakarta, Cairo, Moscow, Sao Paulo and Los Angeles have more than three pollutants that exceed their protection guidelines (Stein 1992).
Noise pollution is another effect on the environment caused by the emergence of the megacities. The large number of people in these cities attracts the construction of many different industries. Most of these industries are run using heavy machinery that cause noise pollution. There is also an increase in the number of vehicles in these megacities due to the increased demand of transport. The constant hooting and the engine sounds of these vehicles are also sources of noise pollution in the megacities. The excessive use of fossil fuels also causes the depletion of their reserves. The naturally occurring resources such as trees and fossil fuels are used in large amounts in these megacities to sustain the daily human activities. Their continuous exploitation leads to their depletion (Stephen 2005).
Soil contamination is also rampant in the megacities. The soil is contaminated by the acid rains that are caused by the increased amounts of acidic gases in the atmosphere. These acid rains alter the potential hydrogen of the soils hence affecting the quality and types of crops grown in these regions. Most of the soil is also contaminated with wastes from the industries. The contamination of soil reduces their quality, which leads to a reduction in their crop production efficiency.
The megacities are home to millions of people. This large population keeps on demanding more houses, food and energy. Therefore, forests are cleared to cater for these needs. The trees are cut down for charcoal production, and the cleared land used for construction of houses and planting crops. However, this results into a more serious problem of deforestation and the destruction of natural ecosystems. The trees in the forests are essential. They are involved in balancing of the levels of atmospheric oxygen and carbon dioxide. When cut down, the balance of atmospheric oxygen and carbon dioxide is not maintained leading to an increase in atmospheric pollution. There is an increased amount of atmospheric carbon dioxide that causes acidic rain. The level of soil pollution also increases due to the effect of acid rains (Angel and Civco 2005).
Megacities cause the extinction of some species of animals. As discussed earlier, there is a high rate of deforestation to clear space for the increased demand for houses. The deforestation is done by techniques, which even involve slashing and burning. This destroys some of the native animals present in an ecosystem. For migrating animals, the migration trends may be changed. This may eventually lead to the extinction of some species due to interference with their reproduction cycles (Aguilar & Escamilla 1999).
Megacities have also actively contributed to global warming. The large amounts of greenhouse gases, released by motor vehicles and industries located in the megacities, settles into the atmosphere. They form a blanket of gases in the atmosphere and cause the greenhouse effect. The greenhouse effect results to an increase in the temperatures of the earth. This increase of the earth’s temperature, commonly called global warming, causes a rise in the sea levels, expands the subtropical deserts and occurrence of heat waves. Global warming also causes heavy rainfall that leads to floods, droughts and extreme changes in the yield of crops.
The high amounts of waste that are produced in these megacities cause problems of waste management. The wastes are usually dumped in sites located within the cities. In Nairobi, there is a large dump site located in the region of Dandora. This dump site is a real health hazard as it is located in an open area in a highly populated city. It is the cause of many air borne diseases acquired by the inhabitants of this city (Pick and Butler 1997).
The emergence of slums is another problem that is caused by the expansion of megacities. As more and more people move into the urban areas from the rural areas, the number of houses available decreases. This large population of people requires housing and it ends up setting up substandard houses as their settlements. The decrease of land per an individual causes the quality houses being built to be compromised. Therefore, the megacities are categorised by numerous closely built residential houses (Bugliarello 1994).
There are socio-economic differences between people in the megacities. This is characterised by the wide range of social fragmentations and social standards. There also exists socio-cultural conflicts due to the differences in the backgrounds of the inhabitants. Most of the people living in these cities originate from different rural areas. These people come seeking for jobs and the joys of the urban life. This usually results into clashes of cultures and religions amongst the inhabitants. The conflicts, which are usually found in these communities, cause the breakup of many ties. This results in a loss of the sense of social cooperation, which leads to the anti-social behaviours witnessed among many megacity dwellers. This lack of cooperation causes challenges for law enforcers when they are fighting crime. The antisocial behaviour is well characterised by the fact that most megacity dwellers do not have close relations with their neighbours (Angel and Civco 2005).
Most of the megacities are characterised by high crime rates. Mexico City is one of the leading cities in drug trafficking. One of the main reasons for this high crime rate is the economic state of the inhabitants of megacities. Most of the megacity dwellers are low income earners. There is also a significantly large small population of middle income earners. Most of these crimes are carried out by the poor inhabitants, who are trying all means to make ends meet and survive. The unequal distribution of resources leaves many of the megacity dwellers living in deplorable conditions. They live below the poverty line and watch others live in luxury. This has caused an increase in crime level in these cities, with most of the crimes being violent. A large population of megacity inhabitants is also unemployed. The unemployment rates in the megacities are highest in Haiti, Peru and Cuba (Angel and Civco 2005).
Most of the people engaged in crimes and drug trafficking are aged between fifteen to twenty four. This is the age, at which most kids go to school. However, the majority do not attend school. This idleness is also another factor that compels them to engage in crime and criminal activities. A vicious cycle of crime develops in the megacities. Most of the inhabitants grow up witnessing crimes being committed in their cities. They experience brutal murders, mass murders and violence. These helps them to become acquainted with crime, and thereafter easily engage in it. The youths also quit school after the primary level of education. This leaves violence as their only educator. Therefore, most of these youths find themselves in the drug dealing business both for the money and due to the lack of other business options (Brockerhoff and Brennan 1998).
Megacities have higher crime rates compared to other cities. Rio de Janeiro, for example, is known to have the highest crime rate in Brazil. In the year 2007, 2,273 people were killed in Rio. This is a murder rate of 37.7 people per one hundred thousand people. In the same year, police killed one thousand; three hundred and thirty people in the same city. In Mexico City, there was an average of four hundred and nine crimes reported daily in the year 2006. Despite this alarming numbers, only ten percent of the crimes are reported to the police. This implies that, in 2006, possible four thousand and ninety crimes were committed on a daily basis. In Sao Paulo, a megacity in Brazil, the criminal homicide rate was thirty five percent per one hundred thousand people in the year 1999 (Lance 2007).
Most of the young people in the megacities choose to abandon school and work in illegal businesses of drug trafficking. The high numbers of school dropouts have caused a higher rate of illiteracy in the megacities compared to other cities. The megacities are also characterised by high rates of drug and alcohol addiction. This is because these commodities are easy to acquire. They are also cheap, affordable and in constant circulation. Most of the unemployed youths turn to drugs as a form of solace and consolation. Others get addicted to drugs and always turn to them when they are overwhelmed by the day to day hardships.
The combined effects of social and environmental problems in the megacities cause its inhabitants to have a low life expectancy. Most of the inhabitants of these megacities are poor and cannot afford basic health facilities. In Mexico City, the World Bank reported that, in the year 2004, eleven percent of the city’s population was extremely poor. Fourty two percent of the inhabitants were said to be moderately poor. The life expectancy of the people in these megacities is lower compared to those living in other cities. In Mexico City, the life expectancy is seventy five years, seventy six years in Cuba and seventy one years in Rio de Janeiro (Elsom 1992).
It is evident that megacities are dynamic and complex systems that are becoming increasingly popular in the modern life. The ever increasing population of the world means that the number of megacities will continue to increase. Therefore, megacities are crucial for growth of the economy and the sustainability of the present and the future generations. Their negative environmental effects should be continually addressed and corrected. The living conditions in these cities should be made safe for habitation. Measures should also be derived to curb the rate of pollution and reduce the rate of crime in these megacities. The economic input of megacities to the countries they exist in is significant. However, the inhabitants should be protected from the hazardous pollutants. This will ensure maximum productivity of the workers.
With those factors considered, megacities are not to be seen as threats of environmental and social degradation; they hold the promise of a sustainable future. They steer the growth of a country’s economy and social development. Therefore, efforts should be directed to making them well-suited to fulfil their imminent promise.