Urban social and environmental issues

An informal settlement is an area of self-built, unplanned housing constructed by residents on land they do not legally own or rent (insecure tenure), usually without official permission, planning or basic services such as piped water, sanitation and electricity.

Also known as a squatter settlement, slum or shanty town, examples include Dharavi in Mumbai and Kibera in Nairobi.

The urban heat island is the tendency for a built-up city to be several degrees warmer than the surrounding rural areas, especially at night.

It occurs because concrete, tarmac and buildings absorb and store heat, there is less vegetation and water to cool the air, and traffic, industry and air conditioning release additional heat into the city.

Air pollution — heavy traffic, industry with weak emission controls and the burning of biomass and waste release smoke, gases and fine particulates, producing smog that harms health (e.g. Delhi regularly exceeds WHO safe limits).

Water pollution and solid-waste build-up — sewage and industrial effluent enter rivers, and inadequate waste collection means rubbish accumulates in streets and waterways, spreading disease and clogging drains.

Loss of green space and the urban heat island — land is built over so parks and vegetation are lost, and the mass of concrete and tarmac makes the city several degrees warmer than the surrounding countryside.

In many informal settlements there is no proper sewerage system or private toilets, so human waste is disposed of in open drains, pit latrines or nearby waterways — often close to where people collect and store water.

This sewage carries pathogens (for example Vibrio cholerae, which causes cholera). The waste contaminates the water supply — shallow wells, standpipes and rivers — because there is no separation between sewage and drinking water.

Residents then drink, cook and wash with the contaminated water, so the pathogens are ingested via the faecal–oral route and cause cholera, typhoid and diarrhoeal disease. In crowded conditions the disease spreads rapidly from person to person.

The result is severe diarrhoea and dehydration; with limited healthcare and little clean water for rehydration, this can be fatal, particularly for young children — the clear chain of no sanitation → contaminated water → disease → death.

The resource shows that the city's air pollution is extremely severe: an annual average fine-particulate (PM2.5) concentration of about 100 micrograms per cubic metre is twenty times the WHO guideline of 5, meaning residents are continuously exposed to dangerously polluted air.

Such high particulate levels are typical of rapidly growing cities where traffic, industry with weak emission controls and the burning of biomass and waste all release fine particulates faster than they can disperse. Because the value is an annual average, exposure is long-term and chronic, not a one-off spike.

The likely effects are serious for health: PM2.5 is small enough to be inhaled deep into the lungs and enter the bloodstream, causing and worsening respiratory diseases (asthma, bronchitis, lung cancer) and cardiovascular disease, with children and the elderly most vulnerable. Twenty times the guideline implies a large burden of premature deaths and ill health across millions of residents.

For the city this also means higher healthcare costs, lost working days and reduced quality of life, so the pollution shown in the resource is both a health and an economic problem that management (cleaner transport, emission controls) would need to address.

In rapidly growing cities the benefits of growth are very unevenly shared, producing a small wealthy group and a large low-income majority — a wide income and wealth gap. Because people can only afford housing that matches their income, this inequality becomes written into the map of the city.

The wealthy cluster in planned, high-quality neighbourhoods — often gated communities with private water, electricity and security guards — effectively buying their way out of failing public services. Land and property there are expensive, which excludes the poor.

The poor, unable to afford formal housing, are pushed into informal settlements and slums on cheap, marginal land, where services are lacking. Many rely on the insecure, low-paid informal economy (street vending, recycling, casual labour), which keeps them trapped in poverty.

The result is spatial segregation: rich and poor live in separate districts with sharply different housing, services and opportunities. This separation can entrench inequality across generations and fuel resentment, social tension and crime, because the two groups share the same city but not the same life chances.

Providing clean water, sanitation, electricity, healthcare, education and waste collection to everyone in a rapidly growing city is extremely difficult, mainly because demand grows faster than services can be built.

First, the population is rising very quickly through rural–urban migration and high natural increase, so the number of people needing services outpaces the rate at which pipes, power lines, clinics and schools can be installed. The city is always trying to catch up.

Second, city authorities in lower-income countries often lack the money, trained staff and administrative capacity to fund and manage large infrastructure, and much of the population pays little tax (working in the informal economy), so the revenue to pay for services is limited.

Third, much of the growth is in informal settlements built illegally on marginal land. These areas are unplanned and densely packed, making it physically hard and expensive to lay pipes and cables, and authorities may refuse to service illegal settlements because residents have no legal land tenure.

As a result, provision is partial and unequal: standpipes and shared latrines instead of piped water and sewerage, intermittent electricity, and too few clinics and schools. The combination of rapid growth, weak finances and unplanned informal expansion means the service gap persists and often widens.

Rapidly growing cities face a cluster of overlapping problems — housing shortages, inadequate services, social inequality and environmental degradation — and this answer assesses whether housing is truly the most serious before reaching a judgement.

The case that housing is the most serious problem. When growth outstrips the supply of affordable homes, millions end up in informal settlements such as Dharavi (Mumbai) or Kibera (Nairobi) — overcrowded, self-built and on unsafe land. Housing is arguably the root problem because so many other issues flow from it: informal housing is exactly where clean water and sanitation are missing, waste piles up and disease spreads. Fix housing well (with services) and many linked problems ease, which is why it can be seen as the central issue.

The case that other problems are as serious or more so. However, the health impacts of poor services and pollution may be more immediately deadly. Contaminated water causes cholera and diarrhoeal disease, and air pollution in cities such as Delhi (regularly exceeding WHO limits) contributes to millions of premature deaths worldwide — harms that kill even people who have shelter. Social inequality, unemployment and crime can destabilise a whole city, and environmental problems (water pollution, the urban heat island, waste) damage the wider population and economy. These problems also affect residents of formal housing, so they are not simply a by-product of housing.

The interconnection. In reality the problems are deeply interlinked: poor housing, missing services, inequality and environmental damage reinforce one another, and their common cause is growth outpacing planning, funding and jobs. Ranking one as 'most serious' can be misleading.

Conclusion. On balance, housing is the most visible and arguably the foundational problem, because informal settlements concentrate the worst service and health conditions. However, it is not straightforwardly the most serious in terms of harm — the health effects of unsafe water and air pollution can be more immediately lethal. The most accurate view is that housing is the central problem from which many others stem, but it cannot be separated from the linked crises of services, inequality and environment that together define the challenge of rapid urban growth.

Both lower-income and higher-income cities face social and environmental problems, but their scale, nature and manageability differ because of contrasts in wealth, governance and the pace of growth. This answer assesses how far the problems really differ, using a rapidly growing megacity such as Mumbai (India) and a higher-income city such as London (UK).

Ways the problems differ sharply. In a fast-growing LIC/NEE city like Mumbai, the problems are severe and basic: huge informal settlements (Dharavi), widespread lack of clean water and sanitation and the waterborne disease that follows, unreliable electricity and very high air pollution from traffic, industry and biomass burning. A large share of people work in the insecure informal economy. Growth is so rapid that provision cannot keep pace, and weak city finances limit what can be done — so problems are large and only partly managed.

By contrast, a higher-income city such as London has near-universal clean water, sanitation and electricity, formal housing for most, and stronger emission controls, so its problems are less about survival and more about quality of life — traffic congestion, some air pollution, waste management, inequality and the cost of housing. Its greater wealth and governance capacity mean it can invest in mass transit, clean-air zones and services that reduce environmental harm.

Ways the problems are similar. However, the differences are not absolute. HIC cities also suffer air pollution, an urban heat island, waste problems, social inequality and housing affordability crises — London breaches air-quality limits and has areas of deprivation. So the types of problem overlap; what differs most is their severity and the capacity to manage them.

Conclusion. On balance, the problems differ substantially in scale and severity but overlap in type. The decisive contrast is wealth and capacity to cope: the lower-income city faces larger, more basic and less controlled social and environmental problems because rapid growth outstrips limited resources, whereas the higher-income city, though not problem-free, can manage similar issues far more effectively. The differences are therefore best explained by level of development and governance rather than by the presence or absence of the problems themselves.