As we saw in the previous story the image of the city as something constructed separately from the natural no longer exists. Yet it has never existed besides in fairy tales. None of the authors of this blog are particularly freaky, but maybe if we make use of an image everything becomes easier. The mythological city of Minas Tirith, where some of the most important events of the last part of Lord of the Rings happen, looks like the one from above.

A walled city, outside of which there is no trace of anything made by man … just untamed nature … as usual: the urban vs. the natural.

But this is pure façade: the inhabitants of Gondor’s capital ate every day, thus the seemingly intact surrounding fields actually should be planted, plowed and cultivated. Man does not only eat vegetables, so we guess there should be farmers who would provide the inhabitants with meat, milk, eggs and other staples. But not everything occurs near the city: fish (although there might be a river) and many other products have to be brought from nearby areas, then these fields would be crossed by roads (Gandalf does not go cross country …) as well as shiploads would arrive through the river pier. The wells in the foothills would be the drinking water supply of the city and nearby forest the places where extracting the necessary fuel to heat homes or preparing food, and so much more.

But this does not end here. The dazzling white Minas Tirith works like other cities, returning to this idealized environment the waste produced in their daily operations: rubbish, organic waste from food preparation, polluted waters after passing through palaces, houses and restaurants (fairies also go to the loo), chimneys smoke releasing CO2 and so on. This is precisely the “urban metabolism:” the amount of resources that a city consumes for daily operation and the waste it returns to the environment as a result of this activity. Therefore Minas Tirith does not exist separated from the natural environment that surrounds it, but forms with it an operating cycle, without which the city would quickly disappear. This is precisely an ecosystem and this city and others will form part of it. Therefore this is no longer urban vs. natural, but the integration of the one into the other.

Traditional cities were aware of this and even if in an intuitive way they were able to maintain a balance, among other things, because the number of people living in them in a concentrated form was much lower than in the countryside. However, this relationship has been reversing during centuries, so cities have now become so large that they can easily unbalance the natural systems of which they are part.

Let’s stop talking about mythological cities and move to the cities that are accompanying us throughout this series, because in relation to urban metabolism it is not only about size but also about the way we live. We have seen in any of the previous stories that this district’s low density of population and events forces you to navigate by motorized means, which in the best case is public transport, but it is usually the car you keep in the garage. Each time you start the car you are not only consuming an energy resource, but you are also giving back to the environment some waste in the form of greenhouse gas emissions. But it is not only you who needs to move … so does the postman/woman, the garbage truck, the delivery person, the local police on its nightly rounds … and for that they use transport networks.

This city model needs that networks of services extend and spread non-stop: each of these houses need potable water (supply network), need to evacuate waste (sewage network), need to plug the TV, laptop… need to talk on the phone and connect to internet (telephone network) besides the fact you get to them through a paved and illuminated street (electricity network). More and more networks spread throughout the territory. So not only these must be built but maintained over time.

Furthermore, if you look at the little houses you will realize they are all surrounded by a small garden that has to be watered daily and a pool to be filled with water and kept clean. The house being surrounded by air on all four sides is like a lonely stove in winter; if it is not properly insulated, it releases heat into the surrounding air, and therefore increases the heating consumption. In the same way, in summer the air conditioning inside tries to counter the effect of the sun on the walls.

There are few cases where these houses purify gray water, collect and reuse rainwater, are oriented or isolated properly avoiding the extra energy to achieve thermal comfort and so on. Nevertheless all this is possible, thus urban metabolism can be improved even in this urbanism based on networks.

Again, to live in a dense and compact area is on the side of sustainability. Obviously this part of the city needs networks, but these are much less extensive and more importantly, will be used more intensively, then will be much more efficient. So buses will transport more passengers and have more stops, garbage trucks will have to travel less distance and dustbins will be more crowded (because more people will live nearby), the police in their daily round may attend more people and faster, a postman/woman can deliver many more letters in less time, 100 meters of potable water pipeline will serve hundreds of homes (and not six), a public park will be the place of recreation for many locals, a lamp will illuminate the night walk of many citizens, not just the way to my neighbor next door in his car back home after work …

Thus we see how the metabolism of our cities affect urban sustainability:

ENVIRONMENTAL SUSTAINABILITY. After what has been mentioned earlier it is almost obvious. In fact this relationship is so obvious that is what has overshadowed other meanings of sustainability: Metabolism = Environment = Sustainability.

SOCIAL SUSTAINABILITY. Production of resources can also be performed within our cities and these places can also be spaces for meetings, casual encounters, social interactions…

CULTURAL SUSTAINABILITY. Being local consumer of resources means knowing and recognizing own values… and one of the most important is, for example, the gastronomy. Knowing which products are those of our land, how they occur (even knowing who produce them) and how they must be cooked is part of a culture which is our own.

ECONOMIC SUSTAINABILITY. Obviously the construction and maintenance of these urban networks entails a significant economic investment, thus a greater efficiency of these will involve a saving which will allow to invest that extra money in other parts of the city.

The ultimate purpose of these articles is that each of us can understand in a fairly intuitive way (and with simple numerical values) how simple choices affect urban sustainability. As you can imagine many of the indicators related to urban metabolism are anything but simple to calculate.

. However, they provide “big numbers” that would be useful to know and remember: a desirable  ENERGY CONSUMPTION of 6000 kWh/ capita per year (considering both private consumption and public) a POTABLE WATER CONSUMPTION for residential uses of 100 liters / capita per day and a WASTE GENERATION less than 1.5 kg / inhabitant per day. Measuring these quantities at home is very simple … you just need invoices of the supplies and a scale in the bathroom.

·There is also another indicator that we can calculate and assimilate very easily. Today, at least in the Spanish context, separation of waste must be done at source. Everything that we do not separate ourselves at home will end up buried underground, so in this case the minimization of waste production is directly dependent on our actions. The importance of this action is that separating waste turns it into a resource in itself and therefore we are imitating natural circular processes. Besides being conscious, one of the differentiating factors for achieving people to separate waste is to find nearby containers of each of the fractions (paper and cardboard, glass, light packaging, organic matter and rest). So the indicator PROXIMITY TO WASTE COLLECTION POINTS

indicates that at least 80% of the population of the city should find those five containers at a distance less than 150 meters from the door of their homes. Is this your case?

To get more technical information about these indicators you can look up pages 563-565, 573-576 and 581-588 of Guía Metodológica para los Sistemas de Auditoría, Certificación o Acreditación de la Calidad y Sostenibilidad en el Medio Urbano.