No one disputes the exponential urban population growth the world is experiencing and its dramatic consequences if we do not act now. Neither does anyone question that good urban planning and design can shape the urban fabric, to accommodate the expected population growth in cities, mostly in developing countries.

Indeed, it is very comforting to learn from my discussions with national and local leaders, as well as academics and civil society actors, of the general consensus over the transformative power of well-planned and designed urbanization. This is very good news! And Habitat III is set to present this historical paradigm shift of urbanization as a tool for development.

What is still unknown to date, however, are the consequences of unsustainable urban development and unplanned city growth. A recent study conducted by United Nations-Habitat, in collaboration with New York University and the Lincoln Institute for Land Policy, shows that land use in the world’s cities is staggering, particularly in the last 25 years.

Indeed, the results are shocking. In developed countries, the urban land use increased by 80 percent, in comparison with the 23 percent urban population growth rate between 1990 and 2015, an increase of more than three times. The trend in developing countries is also similar, as urban land use increased 3.5 times while the urban population doubled.

Cities grew much more in area than in population, in both developing and developed countries between 1990 and 2015, as a clear evidence of the absence of well-planned urbanization and the alternative proliferation of spontaneous city growth.

This information should be kept in mind alongside the fact that population growth in the world is predicted to be highest in developing countries. An estimated 94 percent of the population growth is expected to take place in Africa and Asia, with Latin America slightly less. With the current urbanization trends, countries from the Global South are expected to take up large amounts of urban and peri-urban land in the near future.

A second finding, intimately related to the use of land, is the corresponding declining density of the world’s cities, both in developed and developing countries. City densities have declined at an annual average rate of 2.1 percent in developing countries and 1.5 percent in developed countries. In other words, this means densities have decreased by 52.5 percent and 37.5 percent in developed and developing countries, respectively.

Obviously this is not very good news for the sustainability of our planet and gives rise to serious questions that I would like to reflect upon, now, in the last stretch towards Habitat III.

Urban sprawl and reduced urban density in the world occurred for several reasons, namely in lifestyle, with suburbialization both for the rich (gated communities) and the poor (mass housing schemes), land speculation and spontaneous and informal land occupation worldwide.

Let us look at the case of a specific city in Asia. In 2000 city ¨A¨ urban area was 286 km2. According to its master plan approved in 2009, this was expected to reach 400 km2 by 2020. In fact it reached 612 km2 by 2015. This case is not an exception; on the contrary, this illustrates well what is happening in many cities from North to South and from East to West.

The consequences of excessive urban expansion and a corresponding decrease in density have contributed to everything but good and sustainable urbanization: increased demand for mobility and consumption of energy; environmental degradation; augmentation in costs of urban services per capita (water, sanitation and drainage); increased cost of public space and infrastructure per capita and decreased productivity of urbanization, with less economies of agglomeration.

Hopefully, we are just in time to reverse these unsustainable trends. There are no magical recipes for urbanization. However, with more than forty years of experience, at UN-Habitat we have identified a three pronged strategy that provides a frame to address these challenges. These are: adequate and implementable rules and regulations; good planning and design; and a sound municipal finance plan.

This is the important subject of discussion and debate on the way towards Habitat III in Quito this October. In connection with the Sustainable Development Goals (SDGs) approved in New York last September and the Paris Climate agreement in December, it is time now to focus on the specific measures that we need to introduce to the current model of urbanization in order to achieve the noble objectives agreed both in New York and in Paris. It is time to add Quito to the list.

Dr. Joan Clos is Secretary General of Habitat III and Executive Director of UN-Habitat