Why are cities expanding?

What cities for tomorrow? Controlling urban sprawl and rethinking the city

février 2018

Agence pour l’Environnement et la Maîtrise de l’Energie (ADEME)

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Our cities are spreading out, so what?

Whereas in the 19th century, 80% of the population lived in the countryside, today nearly 70% of French people live in urban areas.

Since the end of the 1960s, cities have been expanding, in particular to accommodate a growing population. This is known as urban sprawl. This urban sprawl has repercussions on our lives and our environment: reduction of natural and agricultural land, deterioration of biodiversity, increased risk of flooding (because water can no longer penetrate waterproofed soil), difficulty in creating coolness in the city in periods of high heat, significant damage during more frequent natural disasters, etc. Today, regulations encourage the economical management of space. A multitude of strategies and actions are being taken to make our cities more sustainable and pleasant to live in without extending them any further, while at the same time contributing to the fight against climate change. How can we slow down or even stop urban sprawl? How can we make cities sustainable, pleasant to live in and accessible to all?

The appeal of suburban areas

Lifestyles are changing

There are more and more of us and the lifestyles of the last few decades have greatly modified our use of space: the demand for housing, transport, local services and parking space continues to grow. The evolution of family models (single-parent families, home care for the elderly, etc.) also leads to a greater need for housing.

Individual housing in demand

Moving away from the city centre, it is easier to find detached houses with a private garden, which allows you to be closer to nature and more peaceful. Unfortunately, this type of housing takes up much more space than a flat in the city to accommodate the same number of people.

Cheaper housing

The cost of housing in the city centre is often high. This leads people to look for housing further away in some of the still affordable suburbs, especially if they want to become homeowners. However, living in the suburbs usually increases commuting costs, especially when two cars are needed per household.

Economic activities and transport, major consumers of space

Urban sprawl is not only linked to housing construction. Economic activities and transport infrastructures account for almost two thirds of the land artificially developed in France. Economic activities and transport infrastructures are also responsible for a significant proportion of soil sealing. Of all the new surfaces sealed between 1992 and 2004, 37% were used for transport infrastructures, 33% for economic activities and 29% for housing.

What are the consequences?

Urban sprawl and the resulting increase in sealed surfaces have major consequences for the environment and its inhabitants.

A threat to soil and biodiversity

Sealing degrades soils

Sealed soils no longer allow sufficient rainwater to penetrate. Without air and water, micro-organisms can no longer thrive. The soil is rapidly impoverished and degraded. Soil is a fragile natural heritage that has taken thousands of years to build up and which plays a part in the regulation of carbon and the water cycle. It is the basis of life in all terrestrial ecosystems. It is therefore necessary to protect it.

Sealing disrupts biodiversity

Railways and roads can form barriers that are difficult to cross for certain animals that can no longer follow their usual path (seasonal migrations, reproduction periods, etc.). This can lead to the isolation of species and, consequently, reduce biological diversity. In mainland France, it is estimated that 9% of mammals, 24% of reptiles and 23% of amphibians are now threatened with extinction.

Health risks

Increasingly polluted air

Many people who have chosen to live on the outskirts of cities live far from their place of work. Public transport or other modes of active mobility such as cycling, for example, are not always easily accessible and the private car is still the preferred solution. Over the last few decades, road traffic and traffic jams at peak times have continued to increase: in the Ile-de-France region, there are on average 300 kilometres of traffic jams at peak times. Added to the pollution emitted by the heating of buildings and industries, the emissions of pollutants from transport further degrade the quality of the air we breathe. The World Health Organisation estimates that 80% of city dwellers are exposed to poor air quality.

Noise, a real nuisance

The National Noise Council (CNB) and ADEME estimate that more than 25 million people in France are significantly affected by transport noise, including 9 million exposed to levels that are critical to their health (sleep disturbance, stress, etc.).

Impacts on the climate

Daily transport between homes and workplaces generates significant greenhouse gas emissions. Single-family houses in the suburbs consume more energy (gas, oil, electricity) for heating than flats in the city. This is because houses have all their facades exposed to the cold and wind, whereas in flats the party walls are not exposed. Greenhouse gas emissions due to heating are therefore greater with the increase in the number of single-family homes. The concentration of greenhouse gases in the atmosphere leads to global warming and climate change.

Increased sensitivity to heat waves and floods

Due to climate change, extreme events (heat waves, heavy rainfall) are becoming more frequent. During hot spells, we have more difficulty cooling our homes, particularly in city centres, because the nights are warmer there than in the countryside (little vegetation, less air circulation, artificial ground, etc.). This is what is known as « urban overheating ». During episodes of heavy rainfall, the risk of flooding in urban areas is higher because the water can hardly be absorbed by the waterproofed soil. It runs off in large quantities towards the lowest points and the watercourses which quickly overflow.

Disappearing agricultural land

The expansion of cities mainly takes place at the expense of agricultural land and, to a lesser extent, of meadows and forests. Agricultural land is needed for crops and livestock. We are already seeing the negative impact of climate change on the yields of several crops: wheat, rice, soya and maize… At the current rate, it is estimated that yields will fall by 2% every 10 years, which could have consequences for the price of raw materials and the security of supply. Preserving sufficient arable land is therefore essential to adapt to climate change.

Less diversity

In peripheral areas, people rarely live close to their workplace and shops. The further away from the city centre, the less ‘functional mix’ there is. On the outskirts, there is often less social diversity linked to property prices and the financial capacities of households. City centres are becoming more gentrified; the middle classes and the lower classes are moving to more accessible suburbs.

Costs for communities and taxpayers

When you build in an already urbanised area, you use the existing networks and roads. Conversely, when building on new surfaces, it becomes necessary to build and maintain new roads, to extend the water and sewerage networks, etc. All this has a significant cost for communities, which is passed on to taxpayers.

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