Projections of Urban Growth Highlight at Risk Areas


Forecasts of different regions’ likelihood of urban expansion could be used to direct conservation efforts

Researchers are trying to make detailed predictions about how urban areas are likely to grow in order to forecast how the next few decades of urbanization will affect biodiversity.

The scientists published their findings in the journal Proceedings of the National Academy of Sciences. The biggest changes are currently occurring in developing countries. The UN predicts that cities will absorb all of the world’s population growth, which is about 2.3 billion people, in the next four decades. However, these predictions don’t account for variations in how the individual cities will change and evolve to meet this growth.


Karen Seto, a geographer at Yale University, in New Haven, Connecticut, and her team looked closely at how cities grow. They focused on the expansion of urban spaces, not population growth. They started with NASA satellite images from twelve years ago, as well as population-density estimates from NASA’s Global Rural-Urban Mapping Project, in order to establish a baseline distribution of city-dwellers.

They then used UN country-level urbanization projections, coupled with economic-growth projections from the Intergovernmental Panel on Climate Change. Finally, they assigned population-projection uncertainties derived from the National Research Council.

This yielded a model that assigned a probability of urbanization to a 25-square-kilometer (10-square-mile) block all over the globe. The team discovered that wide-ranging urbanization was likely to occur in eastern China and tropical Africa. On the other hand, Mexico can expect most of its population growth to occur on land that has already been developed.

This map could be used to guide conservation policies, states Seto, helping policy-makers prioritize regions to protect from urbanization in order to shape the urbanization flow. The team overlaid global maps of biodiversity to show where extensive urban expansion was likely to threaten biodiversity. Urbanization in the Guinean forests of West Africa is likely to consume at least 6.8% of that hotspot.

Reference: “Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools” by Karen C. Seto, Burak Güneralp and Lucy R. Hutyra, 17 September 2012, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.1211658109

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