Environmental driving forces of urban growth and development: An emergy-based assessment of the city of Rome, Italy

Large urban systems can be considered as the final point of convergence of resources, environmental services and human activities from rural settlements to villages to towns to small and big cities. The emergy synthesis method is applied in order to capture the complexity of urban systems from the point of view of the larger scale, the geobiosphere, where resources come from. Emergy is the total available energy of one kind (usually solar) directly or indirectly used up to drive a system or a process. It can be considered as a measure of a system's demand for environmental support. The population of Rome is 4.43% of total Italian population, with an emergy use of about 4% of total emergy supporting the Italian economy. Emergy use per capita is 5.50E+16 seJ/year, compared to an average value for Italy of 3.60E+16 seJ/year. An empower density of 1.09E+14 seJ/m2/year was calculated for Rome, much higher than for average Italy, 6.86E+12 seJ/m2/year. Finally, the emergy/GDP, an indirect measure of economic performance of the system, is 2.43E+12 seJ/€ for Rome compared to 1.64E+12 seJ/€ for Italy, suggesting that in an urban system (generally characterized by a larger fraction of tertiary activities) the required environmental support for the generation of economic results is much higher than for the whole economic system. Finally, comparison of above performance indicators with similar studies published by other authors (Taipei, San Juan and Macao) points out that Rome has the highest annual emergy per capita (suggesting higher potential standard of living).