Trade Lane Megacities. Urbanismo cuantitativo (1).La ciudad tecnocrática es grande y desarrollada.

Hace unas entradas nos preguntábamos cómo sería una ciudad planificada de acuerdo a criterios estrictamente energéticos y añadimos ahora ambientales o ecológicos (a esta ciudad la llamábamos la ciudad tecnocrática). En dos papers parecen sugerir que la ciudad tecnocrática sería de gran tamaño y economía desarrollada.

1. En este primer paper de 2007, utilizando una analogía biológica, argumentan que esa ciudad sería grande.

Cities as consumers of energy and resources and producers of artifacts, information, and waste have often been compared with biological entities, in both classical studies in urban sociology (14, 35) and in recent research concerned with urban ecosystems and sustainable development. Recent analogies include cities as ‘‘living systems’’ (36) or ‘‘organisms’’ (37) and notions of urban ‘‘ecosystems’’ (38) and urban ‘‘metabolism’’ (17, 38–40). Are these terms just qualitative metaphors, or is there quantitative and predictive substance in the implication that social organizations are extensions of biology, satisfying similar principles and constraints? Are the structures and dynamics that evolved with human socialization fundamentally different from those in biology? 

Answers to these questions provide a framework for the construction of a quantitative theory of the average city, which would incorporate, for example, the roles of innovation and economies of scale and predictions for growth trajectories, levels of social and economic development, and ecological footprints. To set the stage, consider first some relevant scaling relations characterizing biological organisms. Despite its amazing diversity and complexity, life manifests an extraordinary simplicity and universality in how key structural and dynamical processes scale across a broad spectrum of phenomena and an immense range of energy and mass scales covering 20 orders of magnitude. 

Remarkably, almost all physiological characteristics of biological organisms scale with body mass, M, as a power law whose exponent is typically a multiple of 1/4 (which generalizes to 1/(d  1) in d-dimensions). For example, metabolic rate, B, (the power required to sustain the organism) scales as B M3/4 (32, 33). Because metabolic rate per unit mass, B/M M1/4, decreases with body size, this relationship implies an economy of scale in energy consumption: larger organisms consume less energy per unit time and per unit mass. The predominance and universality of quarter-power scaling have been understood as a manifestation of general underlying principles that constrain the dynamics and geometry of distribution networks within organisms (e.g., the circulatory system). Highly complex, selfsustaining structures, whether cells, organisms, or cities, require close integration of enormous numbers of constituent units that need efficient servicing. To accomplish this integration, life at all scales is sustained by optimized, space-filling, hierarchical branching networks (32, 41), which grow with the size of the organism as uniquely specified approximately self-similar structures.

Because these networks, e.g., the vascular systems of animals and plants, determine the rates at which energy is delivered to functional terminal units (cells), they set the pace of physiological processes as scaling functions of the size of the organism. Thus, the self-similar nature of resource distribution
networks, common to all organisms, provides the basis for a

Básicamente vienen a decir que algunos rasgos (variables) de las ciudades están sujetos a rendimientos crecientes con el tamaño (es decir aumentan más que proporcionalmente con aumentos en el tamaño  de la ciudad, cómo por ejemplo el PIB de la ciudad) y otros a rendimientos decrecientes (menos que proporcionalmente, cómo por ejemplo el consumo de gasolina). Ojo, no todos los efectos del mayor tamaño son positivos (crimen, tráfico y epidemias de deben de anotar en el haber).

Creo que no dicen nada sobre otros parámetros que a nosotros nos interesan más cómo la forma (altura) y sobre todo la localización, pero muy interesante artículo, que merece una lectura en profundidad. Creo que el abstract tiene una pequeña errata, pero lo copio tal cuál.

Título. Growth, innovation, scaling and the pace of life in cities.

Abstract. 

Humanity has just crossed a major landmark in its history with the majority of people now living in cities. Cities have long been known to be society’s predominant engine of innovation and wealth creation, yet they are also its main source of crime, pollution, and disease. The inexorable trend toward urbanization worldwide presents an urgent challenge for developing a predictive, quantitative theory of urban organization and sustainable development.

Here we present empirical evidence indicating that the processes relating urbanization to economic development and knowledge creation are very general, being shared by all cities belonging to the same urban system and sustained across different nations and times. Many diverse properties of cities from patent production and personal income to electrical cable length are
shown to be power law functions of population size with scaling exponents, that fall into distinct universality classes.

Quantities reflecting wealth creation and innovation have  Beta <=> 1.2 >1 (increasing returns), whereas those accounting for infrastructure display Beta <=> 0.8<1 (economies of scale). We predict that the pace of social life in the city increases with population size, in quantitative agreement with data, and we discuss how cities are similar to, and differ from, biological organisms, for which <1.

Finally, we explore possible consequences of these scaling relations by deriving growth equations, which quantify the dramatic difference between growth fueled by innovation versus that driven by economies of scale. This difference suggests that, as population grows, major innovation cycles must be generated at a continually accelerating rate to sustain growth and avoid stagnation or collapse.

2. Alguno de los autores del paper anterior han publicado un artículo en Nature titulado A unified theory of urban living.

Extracto.

So the need is urgent for an integrated, quantitative, predictive, science-based understanding of the dynamics, growth and organization of cities. To combat the multiple threats facing humanity, a ‘grand unified theory of sustainability’ with cities and urbanization at its  core must be developed. Such an ambitious programme requires major international commitment and dedicated transdisciplinary collaboration across science, economics and technology, including business leaders and practitioners, such as planners and designers. Developing a predictive framework applicable to cities around the world is a daunting task, given their extraordinary complexity and diversity. However, we are strongly encouraged that this might be possible

Es realmente sorprendente  que esta disciplina que reclaman en 2010 no exista ya. Ni la gran ciudad, ni los problemas energéticos ni los ambientales son cosa de antes de ayer.

Pero según se deduce de su lectura no es poco lo que se sabe ya. Muy interesante. El más interesante de los tres. No obstante se olvidan que además de factores tecnológicos, económicos y sociales hay factores políticos que afectan al desarrollo de las ciudades: los que planifican y ejecutan las políticas urbanas están también sujetos a restricciones políticas.

3. Finalmente, en este tercer paper relacionan el tamaño de la ciudad con las emisiones de CO2 y en este caso parece que lo importante es el nivel de desarrollo. Aquí depende del nivel de desarrollo.

Título. Cities as nuclei of stability.

Abstract. 

Analyzing CO2 emission inventories of 256 cities from 33 countries we find
power-law correlations between the emissions and city size, measured in population. The results suggest that in developing countries more CO2 per capita is emitted in large cities, i.e. they tend to exhibit super-linear correlations and doubling the population of any city implies up to 110% increase of emissions.

For developed countries the results suggest the opposite, i.e. linear or
sub-linear correlations, implying better efficiency of large cities, doubling the
population of any city implies only 80% increase of emissions. The transition
occurs at approx. 10, 000$ GDP/cap. We derive how the total emissions of an
entire country relate with the power-law correlations and find that the size of
the most populated city is dominating in the case of linear and super-linear
correlations. The size of the largest city has no influence in the case of sublinear correlations.

We conclude that from the climate change mitigation point of view,  urbanization is desirable in developed countries and should be accompanied by efficiency increasing mechanisms in developing countries. More data acquisition is needed to support our empirical findings.

Extracto. 

In other words, in economically stronger countries, large cities tend to be more efficient and in economically weaker countries large cities tend to be more inefficient in terms of CO2 emissions per capita.

Hasta aquí los datos cuantitativos. Aunque apuntan algunas hipótesis para explicar esta disparidad, ninguna es concluyente. No comentan la hipótesis de la altura. Las ciudades grandes de países subdesarrollados son, en general, de menor altura (China podría ser una excepción, pero precisamente las ciudades más ricas de China son las más elevadas). Quizás esto tenga que ver con las emisiones.

A mi la comparación que me parecería más interesante es entre emisiones de ciudad grande y la misma cantidad de gente, con la misma cantidad de interacciones en hábitats más y más dispersos (por ejemplo 2 ciudades grandes a una distancia X, 3 a una distancia Y etc…), en cualquiera de los dos casos, países en vías desarrollo y desarrollados.

P.s. visto en Naukas.

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