A complexity indicator based on the diversity of energy and resource uses by a system is proposed in this paper. The indicator is an emergy-based index of complexity derived from a modified Shannon information formula that provides a quantitative assessment of the diversity of sources. The emergy approach assigns to each driving input a weight that derives from the environmental work performed by nature in order to generate such resource. This quality assessment goes far beyond the simple accounting of mass and energy of input flows, but takes into proper account their interlinkage with the biosphere dynamics. The rationale of the proposed indicator is that complexity cannot be assessed by simply counting individuals, species and processes, but requires that focus is placed on several aspects of resource flows, namely their amount, frequency, and quality. Different mixes of emergy input flows originate different levels of growth and complexity. Systems that only rely on a small set of sources out of the large number potentially available possess a built-in fragility, that may determine their collapse in times of shrinking or changing resource basis. For validation purpose, the proposed indicator was applied to the performance of selected national economies (Nicaragua, Latvia, Denmark and Italy) in selected years and of the urban system of Roma (Italy) over a forty-year (1962-2002) historical series. Results point out an increasing complexity of the urban system of Rome over time, while a lower complexity was calculated for the investigated national systems as a whole (likely effect of nationwide averaging), with Italy ranking highest and Latvia lowest. The same assessment performed for the Italian agricultural system over a twenty-year time series (1985-2006) shows a decline of the emergy-adjusted Shannon indicator from about 75% down to 62%, while the decline was from 73% to 63% for the agriculture of Campania region (southern Italy).
The material, energy and environmental flows supporting the growth and welfare of the city of Rome, during a recent forty-year period (from 1962 to 2002) were investigated in order to understand the resource basis of its present welfare and lifestyle. The study focused on the local scale of the urban system (resources actually used within the system's boundary) as well as on the larger regional and national scales where resources come from. Assessing the resource use change over time allowed to understand what are the main drivers of lifestyle changes of the local population. In particular, while the direct, local-scale use of the main material and energy resources exhibits a quadratic growth over time, the total (direct+indirect) consumption on the scale of the global economy is always 3-4 times higher, is so highlighting how much of a city's growth depends on economic and production activities that develop outside of its boundaries. Water use shows an even more alarming trend, in that the indirect consumption grows much faster, suggesting a shift from the use of a less water-intensive mix of products to a different mix that requires much more water in its industrial production. Such trend calls for increased awareness of the water footprint of goods used as well as increased efficiency in water management by both industries and households. The evolution of resource use and standard of living also affects the release of airborne emissions, an issue that is becoming crucial due to concerns for climate change and urban air pollution. The extent of such additional environmental burden is also explored in the present paper.
Results from this study of stability/sustainability conditions of an urban system show that an average citizen of Rome, in one year, uses directly or indirectly as much as 45 tons of abiotic material (minerals, raw fuel, topsoil). Out of such an abiotic flow, about 6.5 tons of fuel per person are required, while the Italian nationwide average is 3.6 tons per year. In addition, 816 tons of water are indirectly used or diverted from their natural pattern in support of individual food, electricity and commodity demand. Despite the scarce 0.05 Ha of productive land available per capita, each citizen in Rome virtually "uses" 4.51 Ha of productive land. Each Roman releases in one year 20 tons CO(2), 50 kg CO, 36 kg NO(x) and 24 kg SO(2), and generates about 450 kg of solid waste, thus contributing in several ways to environmental pollution. Finally, to generate 100 euro of local GDP requires 29 kg of raw oil, an amount that is only paid about 10 euro in the international market.
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