Fuelled mainly by mobility - migration and rural exodus - world urban growth since the middle of the 20th century has beene century at a steady pace. Nearly 70 % of the population will live in cities by 2050, according to the UN. That is to say, in less than a generation. The rapid and uncontrolled growth of the population and urban areas is in conflict with the sustainable development goals (SDOs) defined in 2015 by the United Nations. Thinking the city of the future in a sustainable way has therefore become one of the main challenges of the 21st century.e century.
An 31 October, World Cities Day was held under the motto "Building sustainable and resilient cities". "Every week, 1.4 million people move to the city." underlined on this occasion Antonio Guterres, Secretary General of the United Nations. "This unbridled urbanization can strain the capacities of communities, making them more vulnerable to man-made and natural disasters..
Earthquakes, tsunamis, epidemics: more vulnerable cities
The populations that migrate tend to favour cities that are already massive. While only five cities had more than 10 million inhabitants in 1975, by 2018 there will be 30 cities with a total of 485 million inhabitants - including 19 in the intertropical zone and 22 on the coasts or areas at risk. Cities with more than one million inhabitants have increased from 86 to 600 in the last 70 years.
Yet these mastodons not only compound the inconveniences of high density, but also increase vulnerability to natural and climatic threats - earthquakes, tsunamis, epidemics, floods, tornadoes, landslides - to which are added the risks created by human activities - pollution or industrial disasters, among others.
Some cities, such as Lagos, Istanbul or Osaka, are thus exposed to "multi-risk", i.e. to floods, earthquakes, tsunamis and landslides.
The standardization of our diet
Moreover, the strong imbalance that is developing between urban and rural areas represents a crucial challenge for food security. While the number of farmers is falling sharply, food production is becoming globalized and consumption patterns are becoming more uniform.
According to the Foundation for Nature and MankindThree quarters of our urban food supply consists of twelve plant species and only five animal species. This lack of dietary diversity has implications for the health of populations and the sustainability of our agricultural systems.
Multiplication of shantytowns
Deregulation and the absence of urban policies generate at the same time the development of strong inequalities within the cities themselves: around 40 % of urban growth in the cities of the South involves unconsolidated settlements and limited or non-existent access to basic services. Mexico City, for example, has 4 million slum dwellers, compared to 3.3 million in Cairo. As for Africa, 61 % of the urban population lives in the slums.
There is therefore, not only for environmental but also for human development issues, an urgency to think about these problems. Both for large cities, but also for small and medium-sized cities: faced with the same challenges, these cities do not have the same resources to deal with them, but they are nonetheless the laboratory for interesting innovative solutions: they encourage a change in modes of governance and a stronger involvement of civil society - see for example the initiatives of MercociudadesA network of 400 urban municipalities in South America.
What international response?
In the face of these risks, international organizations are also looking for solutions. Numerous initiatives are thus attempting to support States in their efforts to promote sustainable cities. The Sustainable development objectives or the Mediterranean Strategy for Sustainable Development carried out by the Mediterranean Action Plan are illustrations of this.
COP21 also encouraged the mobilization of local governments: at the December 2015 meeting, a summit of mayors had led to the creation of of the C40 - which brings together the 85 largest cities in the world - from the 100 Resilient Cities - an idea from the Rockefeller Foundation - or from the Mercociudades.
This new involvement of communities illustrates an awareness of the need for action. However, it also shows that the situation calls for contextualized, tailor-made solutions and modes of action for which institutions are not trained.
Unlike the major development models of the 1990s or 2000s, there are no longer any ready-made solutions. The emergence of the sustainable city will therefore take time and will require considerable innovation and reflection on the part of its architects.
In Algeria, an "eco-citizen" city
New international proposals for urban policies, such as SDOs or Habitat IIIs, in fact, are taking this into account and are trying to make their frameworks for governments more flexible.
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Project campaigns - such as the global urban campaign launched after the 1996 Hapitat II conference, which aims at exchanging experiences, or thecities and climate change initiative to strengthen the adaptive capacity of cities in developing countries - wish above all to promote local initiatives and raise awareness among citizens, through participatory experiences and local means.
Improving public spaces can be the first step towards collective awareness, as was to some extent the case with the case in Medellínin Colombia. In Algeria, the construction of Ksar Tafilelt, a new city of more than 10,000 inhabitants in Ghardaïa, was made possible thanks to civil society, because the project mixed local traditions with modernity and aimed at a goal of good living.
Local response to environmental problems
Studies on the mechanisms and impact of climate change, while important, are of little interest to people and institutions in countries of the South because they are carried out on too large a scale. Economic development and the fight against poverty remain the priorities.
In mobilizing social and political science, research must address local responses to environmental problems. In cities in particular, it is on lifestyles and education that researchers can help build ways of acting. This means looking at changes in diet, energy behaviour, transport habits, perceptions of the living environment, and identifying levers for action and blocking factors.
There can be no research on climate change without the joint participation of institutions, civil society and business. This is how public policies can evolve towards local and sustained action. The research agenda must therefore move towards the modalities of action.
Hubert MazurekDirector of Research, Institute of Research for Development (IRD) With the participation of Elkin Velásquez MonsalveThe Director of the Regional Office for the Caribbean and Latin America (ROLAC), UN-Habitat, is co-author of this article.
Header image : Manila, Philippines / © AFP 2018 NOEL CELIS
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