Can cities really be sustainable?

Introduction

            There is a twofold reality concerning cities. On the one hand, they are the locus of many of our most well-rehearsed national problems (Amin, Massey & Thrift, 2000), but on the other, they can be considered among the brightest stars in the constellation of human achievement (Rees & Wackernagel, 1996). Therefore, they are sinks of challenges, but also sources of creativity and hope (Amin, Massey & Thrift, 2000).

The nature and variety of challenges which cities have faced during their existence have differed widely. At the very beginning, the first human agglomerations or ‘walled cities’ were shelters against invasion, starvation and wild elements. Then the Greco-Roman cities can be considered the origins of politics, democracy and citizenship but also were centres of slavery and injustice. Much later, the Victorian industrial metropolis was locus of poverty, grime and disease as well as generators of moral revolutions (Amin, 2006). Nowadays cities are recognized as being arenas for social inequalities and major causes of natural resource degradation. Moreover, since the first years of the last century, these problems have been increasing due to the progressive urban population growth. In this sense, according to the last World Urbanization Prospect report, within 40 years almost the 70% of the total population will live in cities (World Urbanization Prospects, 2007). As mentioned by Amin (2006), the human condition has become the urban condition, and hence, the future of mankind is now (more than ever) closely linked to the destiny of our cities.

Urban Growth Patterns

“Are there laws which determine the number, size, and distribution of towns?”

W. CHRISTALLER

MAKSE et al. Developped in the 90s a mathematical model (Correlated Percolation Model) that relates the pysical form of a city and the system within which it exits. This was based on the ideas of percolation theory and they took into account two key points.

First, data on population density of actual urban systems are known to conform to the relation ρ(r)= ρ₀e^-λr where r is the radial distance from the urban core, and λ is the density gradient.

Second, in actual urban systems, the development units are not positioned at random. Rather, there exist correlations arisin from the fact that when a development unit is located in a given place, the probability of adjacent development units increases. The next figure shows a qualitatie comparison between the actual urban data and the proposed model.

In addition to the strongly correlation between the morphology of actual urban areas and the urban systems obtained in our simulation, the dynamics of the model shows a remarkable pattern of decentralization, a phenomena that occurs in most of the cities in the world.

The use of fractal or chaotic models leads us to view cities as self-organized systems by local actions instead of designs for a centralized intelligence. This fact could give us a wide variety of valuable information concerning the way cities grow and change, and more importantly, the way they might be planned and managed.