Comparative study of urban eco-efficiency. Case study: Sarrià district - Sant Gervasi

Abstract

Based on the studies referring to the city as a dissipative structure and the information theory applied to the urban environment, this research focuses on the analysis of physical entropy (S), as an indicator of the degree of environmental deterioration generated by the Metabolism of the urban system and its relation with the production of negative entropy or neguentropía (H) that compensates the negative impact on the environment. This type of entropy was related to the Shannon theorem, which allows measuring the amount of information generated by a system, in this case, the neighborhoods to study. The information, expressed in bits, reflects the degree of complexity of the city, which is generally associated with the positive attributes of diverse and compact city models.

The main problem related to this type of evaluation is the lack of disaggregated information at scales lower than those of cities (districts and neighborhoods), mainly with respect to physical entropy indicators such as energy consumption, waste production, among others.

The objective of the study is to develop an example of a comparative environmental assessment methodology, which allows qualifying a specific urban environment in a simplified way, through a ratio applicable at different scales.

This comparative study focuses on the analysis of the Sarriá - Sant Gervasi district of the city of Barcelona and the 6 neighborhoods that comprise it, in which the variables physical entropy (S) and the variable negative entropy (H) were calculated separately. Variable S was simplified only to the calculation of energy consumption by neighborhood and its correspondence in CO2 emissions, and variable S was calculated by applying the Shannon formula to 4 urban indicators related to the complexity and diversity of each neighborhood. For the calculation of S, the data on energy consumption and its correspondence in CO2 emissions at the district level, present in the Barcelona Energy Balance document, available on the website of the energy observatory of the ecology department, were analyzed. urban planning and mobility of the Barcelona city council. From the verification of a series of correlations between the total district energy consumption and indices such as that of gross per capita income and cadastral areas at the city level, a series of linear regression models were generated, through the IBM program SPSS STATICS, with which the data on consumption and CO2 emissions are disaggregated for each neighborhood in the district studied.

Regarding the H index, it was calculated with the Shannon entropy formula, applied to data obtained mainly from the website of the Barcelona City Council's statistics and data department, which are related to the diversity of each neighborhood: Inventory of premises commercial on 1st floor, cadastral premises according to use, academic level of the population, the nationality of the population.

Finally, to calculate the eco-efficiency index, the H / S formula is applied, which divides the results of the annual CO2 production per neighborhood, by the weighted average of the urban complexity calculations for each of the 4 analyzed indices.

The main results can be expressed in the following: The Sant Gervasi - Galvany neighborhood obtained an S index of 1.32 tCO2eq, an H index of 2,127 bits, and an eco-efficiency index of 1,606 tCO2eq / bits. As for the Sarriá neighborhood, it obtained an S index of 0.81 tCO2eq, a magnitude H of 2,256 bits, and an Eco-efficiency index of 2,798 tCO2eq / bits.

From the previous results we can infer that: The neighborhood that obtained the most physical entropy, Sant Gervasi - Galvany, is the least eco-efficient, the information it produces does not compensate for the high CO2 emissions that the commercial and services sector generates. On the other hand, the Sarrià neighborhood is the one that generates the least physical entropy and at the same time is the second most diverse neighborhood in the district.