In 2011, the world's population was more than 7 billion. And half of these lived in towns. In 2030, according United Nations, we’ll be 5 billion urban (over 8.3 billion on earth). So nearly 1.5 billion of additional urban people will stay in towns within two decades.
Forecasts of a research published on September 18 in Proceedings of the National Academy of Sciences (PNAS) of USA reveal that if current trends in population density continue and all areas with high probabilities of urban expansion, then by 2030, urban land cover will increase by 1.2 million km2, nearly tripling the global urban land area circa 2000. Half of this expansion will be in Asia, mainly in China and India. However, it is in Africa where the highest rates forecasted urban growth will take place with an increase of 590% between 2000 and 2030, mainly around the Nile River in Egypt, North of Nigeria, Guinea and North of Victoria Lake and too in Addis Ababa region, in Ethiopia.
That will have many environmental impacts: the deforestation decreasing the carbon pool with more CO2 emissions for land use change.
Biodiversity will also be affected as magnifying cities nibble on the habitats of the animals. Geographic modelling published in the PNAS shows as well that urban territory gain by man will put at risk habitat of some two hundred species of amphibians, of mammals and birds already listed as endangered or endangered critic extinction
The authors point out that their study does not take into account what they call indirect urbanization, to say impact of settlements on their hinterlands: wood supply, agricultural raw materials, deduction in water, burying waste in rural areas, etc. Moreover, consumption of meat of urban population is being greater than that of the rural; so one can expect an increased demand for meat products, with all that implies for feeding the animals, the production of methane by herds, the treatment of manure... Urbanization is therefore far from influence only on spaces where city takes up residence. Other studies should evaluate these cascading effects on a large scale.
In the meantime, the mass urbanisation phenomenon is in an acceleration phase. These are hundreds of billions of dollars that are invested every year in infrastructures, whether for buildings, pathways of communication, and networks of water, gas, power and telecommunications. And when the concrete is poured or the macadam spread, for a long time. To mitigate global impact of the billion and a half additional urban persons that will happen by the year 2030, the authors of the PNAS article suggests priority on the densification of cities rather than their spread. For them, the compact development, in addition to maximally preserve natural areas, presents benefits and reduce energy losses. But the responsible of arrangement of the territory of each region or each country must think quickly because, if they want to limit impact of cities on the environment, response time will be very short. Although urbanization is often considered a local issue, the aggregate global impacts of projected urban expansion will require significant policy changes to affect future growth trajectories to minimize global biodiversity and vegetation carbon losses, according the authors.
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