Figure 1. Maidenhair fern.
Hace muchos años, cuando la vida que hoy conocemos se estaba fraguando, hubo unos microorganismos que se dieron cuenta que era mejor criar en su interior a otros bichitos más pequeños y verdes, de los que solían alimentarse, que comérselos. De esta manera se beneficiaban ambos, el grande, aportando protección, y los pequeñitos, alimento, ya que estos últimos habían logrado descubrir ni más ni menos que la fotosíntesis. Es lo que se llama en biología
Many years ago, when life as we know today was forging, there were some microorganisms that realised it was better to breed inside those green little bugs they use to nourish from than to eat them up. This way both benefited: the bigger ones, providing protection, while the smaller ones provided nourishment, since the latter had just discovered no less than photosynthesis. This is what biologists call “endosymbiosis”, and from that very moment one of the most determinant collaborations in our planet’s life forged: the first plants materialized. It is not that I’m going to rewrite a treatise on Botany before we arrive to what concerns us today, but this theory reminds me very much to the time when the first Neolithic civilizations that lived in dry and warm climates incorporated vegetation to their homes architecture. Inside inner courtyards, close by the well or fountain that supplied with water, these plants would develop the ability to transform this water into freshness. Instead of eating them up, they used the plants to bring climate quality to their homes. This type of dwelling was spread out by Greeks and Romans all through the Mediterranean Sea. Centuries later, the Arabs refined them, including new architectural elements and giving birth to the discipline of gardening. Many years passed since then and, until past century, we kept on copying and improving this architecture and its associated traditional gardening. Cordovan courtyards are the best example. The reasons behind this alliance were forgotten the day we started to control our home’s climate by simply pressing the A/C remote button. Some remained to recall this and have quite a lot to say today (Interview with a “courtyard carer”).
The plant’s ability to refresh the air is nothing of a mistake but a matter of basic physics. At a temperature of 20 º C (68 º F), a vegetable takes 585 kilocalories of heat from the atmosphere per each litre of water that evaporates through its leaves, causing temperature to drop . In a partially controlled enclosure like a courtyard, this simple physical process produces a pocket of freshness during the hot Cordovan summer afternoons. It insulates the house breaking up by the end of the afternoon, as soon as we open the windows inside. The fresh air, laden with essences, flows then into the rooms to freshen them. An inner breeze remains all through the night, even in the most calmed days (Passive Cooling Systems. Technical Assistant to Sustainable Construction (Asistente Técnico para la Construcción Sostenible), ATECOS [i]).
Figure 2. Courtyard in Calle Tafures, 2.
Water is a very singular element at any state and life managed to get good benefit from it. Some of its attributes go unnoticed. The named “latent heat of vaporization” is one of them, a concept we had to memorise when we were kids and that we will be remembering today. We’ve already seen that in order to evaporate a litre of water at 20ºC (68ºF), we need 585 kilocalories. That is the energy we would be spending in an intense hour session of spinning or the heat we would need to add to take 6 litres of water, at 0ºC (32ºF), up to 100ºC (212ºF) (without any change in its liquid state). It is not necessary to bring water to the boil to evaporate it; the process sets off just bringing the water surface into contact with a dry atmosphere. Water molecules trap heat within its surroundings and transform it into steam, making everything around to cool down. That is the way a botijo or the “Canary” still works . In thermodynamics, the phenomenon is known as “adiabatic cooling”. Only ammonia can surpass water’s refrigerant capacity. The process depends on many factors, the most important are «room temperature», «wind speed» and «relative humidity». For example, it is possible to cool a controlled and isolated ambience at a temperature of 35ºC and a relative humidity of 18% by evaporating water until it reaches a 90% of relative humidity.
Figure 3. The adiabatic cooling effect used by plants allows to create outdoor microclimates in places like Cordoba city, besides its torrid summers, when thermometers often surpass 45ºC (113ºF). Accompanied by a proper insulation of the dwelling, temperature decrease below 10ºC (50ºF) allows minimizing the use of air conditioning.
Many living beings have taken advantage of this property in water. Plants manage to keep cool and stay within the temperature range that lets photosynthesis to happen. They use 99%, neither more nor less, of the water consumed for that. Man’s physiology makes use of this mechanism as well and, as a matter of fact, it is a distinctive, since perspiration takes place on the skin itself, something unusual among mammals. Thus, during a spinning session of an hour a person would need to drink a litre of water to evacuate the almost 600 kcal burnt to perform the job from the body. Everything fits and water is what makes it possible.
And not only living beings, individually, use this property; ecosystems, growings, gardens do it too. An adult and healthy ash tree is able to perspire 300 water litres per day (Jan Pokorný et al., 2010 [ii]). One hundred hectares of a healthy and mature ash forest have a refrigerating capacity equal to the potential of a thermic power station as the one from Puente Nuevo, in Cordoba. Waste or blessing? At a global level, evapotranspiration is one of the most important energy exchanging processes in Planet Earth.
Of course, this ability is subject to a wide range of variation and depends on many factors, reaching maximums in areas of dry and warm climate, like the sub continental region of Andalusia. Plant type is one of these variation factors. Trees are usually the vegetables with the highest perspiration rates, since they explore wider areas, both in the atmosphere and in the soil. The species’ choice is very important and, even if the locus conditions are favouring, not all provoke the desired effect upon microclimate. In case of being the suitable specie for the spot and objectives pursued, to freshen, the cooling ability of a tree is optimum since atmosphere cools off several metres above ground level and falls down to cold at its feet. If properly watered, this effect transforms riverbank forests and wooded gardens, not into a city lung, as often said, but into its skin
Cien hectáreas de bosque sano y maduro de fresno tienen el poder de refrigeración equivalente a la potencia de una central térmica como la de Puente Nuevo de Córdoba. ¿Un derroche o una bendición? A nivel global la evapotranspiración es uno de los procesos de intercambio de energía más importante del Planeta Tierra. (Adaptation au changement climatique et optimisation du confort thermique par l’utilisation de recours renouvelables. Association Climatologique de la Moyenne-Garonne et du Sud-Ouest, ACMG [iii]).
Figure 4. In the image, two types of crossing paths. In the trace to the left, air conditioning’s comfort has trivialized the importance of vegetation in climate’s comfort. Author: Javier Hernandez Gallardo.
However, at this point, the reader will have already noticed that the effect starts to be appreciated only when we have an appropriate volume of plants and enough water. Therefore, the cooling power of a single tree in a city street would be like “tears in rain” (Roy Batty in the film Blade Runner). A critical and properly watered mass of vegetation is, in consequence, necessary to transform any place’s microclimate. And for this, there’s many elements able to enhance it: surfaces able to seep rain’s water, fine bearing trees in the streets and non-aggressive pruning, broad, not suffocating tree wells, controlled irrigation, small interspersed gardens, green belts in the city surroundings, crops watered, urban vegetable gardens, roundabouts gardens, green roofs, green facades, big gardens, wooded avenues, etc. Irrigation control is important, not just in terms of quantity, but with regard to frequency and time of day. Thus, from a water-saving point of view, watering at dusk is less efficient but it makes temperature to drop quickly, getting the best refreshing rates in the surroundings. At riverbanks, the refreshing effect multiplies during the summertime, when water’s regime is distributed in narrow, low draught, channels since, this way, trees and bushes take up almost all the space and water drenches a bigger area. In the case of Cordovan courtyards, this critical mass is quite small, since confinement between walls allows the refreshing effect not to dilute. This awards city’s general climate an autonomous and less dependent functioning.
However, despite the importance of green zones and vegetable elements for urban climate, the instrument is not considered in the city planning and has never been seriously taken into account. Meanwhile, many dwellings include a courtyard in their architecture but no plants and water spots, the bioclimatic motor that precisely puts the system to work. Like “Mill of Oblivion” by Gilbert Garcin, in this occasion, the progress is acting as the society Alzheimer’s.
Figure 5. ““Mill of Oblivion” by Gilbert Garcin.
And we haven’t talked about climate change yet. According to prospective studies carried out in Andalusia (XXI Century Andalusia Climate) [iv], climate change scenarios esteem that the average temperature will increase between 2 and 4ºC and most of the increase will fall on spring and autumn seasons. Studies like “Estimation at a detail scale on climate control needs for Andalusia in the context of climate change” [v], predict a 85.8% increase, in a worst case scenario (A2 y CNCM3), in the cooling rate for regions like Cordoba capital, and a 39.7%, in the best one (B1 y CNCM3), by the end of the current century. Precipitation decrease will be a generalized trend as well in the major part of Andalusia, which is quite a dilemma to add to the discourse here exposed.
Figure 6. “Estimation at a detail scale on climate control needs for Andalusia in the context of climate change”. Map of the increase in the potential demand rate of air conditioning where the rise of the energy consumption for «cooling» is considered along with its decrease for «heating».
This reading can cause certain surprise since it goes against many firmly hold stances on water-saving and sustainability principles. However, reflection “is served”: we build cities with sustainable gardens, understanding by these, areas with low consumption of water, a renewable and non-contaminant local resource, while we lock ourselves in our houses and connect an air conditioning device that runs on electricity, an energy that, up to now, is based on a high percentage of non-renewable and contaminant resources that, besides, we must import. The pattern has a perverse impact on to the city: it does emphasize the urban heat island effect [vi].Repercussions on other factors and sectors, such as mobility, quality of life or tourism, are direct and the increase in the cooling hours rate caused by the climate change, is an unbearable extra charge for many homes. The thing is that the concept of sustainability should be dealt within the whole society and not by parts.
Figura 7. A xerophytic garden of plants with very low water requirements is a better solution in terms of microclimate than a space with no vegetation. However, if you really want to transform microclimate in your surroundings, you should design gardens with greater water demands.
Fortunately, facts go ahead of this discourse. Passive and natural cooling systems, among them, those based on plants and irrigation, are something of the past that have started to make way in our society as a long-range technological research tool. More than a retrograde option, this is a tool forgotten at some time that comes back at full strenght. Vertical gardens, green roofs and green structures, microclimate gardening, vegetal air conditioning, indoor gardens, etc. They are all different options coming from the hand of gardening and landscaping to stay, like calamintha.
Figure 8. Guadalquivir River, where it passes through Cordoba, and the green belt of the Sierra Morena are two geographical elements of great value and importance when it comes to softening summer temperatures in the city.
- Diego Peinazo Amo. Residing in Calle Marroquíes, 6 courtyard.
- Francis y Rafael from Tafures, 2 courtyard.
- Javier Marzo Artigas. Universidad de Sevilla
- Jean François Berthoumieu. Association Climatologique de la Moyenne-Garonne et du Sud-Ouest (ACMG)
- Manolo Hernandez Martinez. Red de Información Ambiental de Andalucía (REDIAM).Andalusian Environmental Information Network
- María Fernanda Pita López. Universidad de Sevilla
- Maria Luisa Sillero Almazán. Agencia de Medio Ambiente y Agua (AMAyA).Environment and Water Agency
- Rafael Barón Jiménez. Secretary of the Courtyards Owners Association “Claveles y Gitanillas” from Córdoba
- Rafael Pinilla Muñoz. Consejería de Turismo y Comercio. Delegación Territorial de Córdoba. Junta de Andalucía.Regional Ministry of Tourism and Commerce. Regional Office of Cordoba
- Residents in Community of Calle Tafures, 7
Figura 9. We went from Old Age hygienic insalubrity in the public space (image to the left) to contemporary age climatic insalubrity (image to the right). Manuel Hernandez Martinez.
 It is common to confuse this effect with the one provided by the plant when protects us from the sun’s direct radiation. However, they are two independent capabilities working together in the improvement of climate comfort. This distinguish them from a simple awning.
 The Destiladera is a traditional piece of furniture from the Canary Islands. It consists in a four-cornered piece. It carries a pink volcanic stone on the top that is used to distil water. The stone or basin is really porous, letting the water pass and retaining the impurities. Above, a plant called culantrillo grows. Below is placed the bellied clay pot called bernegal that collects the water and keep it fresh. The pot is usually covered by a small pierced plate. In their traditional and forced migrations to America, Canary people moved the still to this continent as a part of their cultural background. In Cuba and Venezuela mostly, we can find the destiladera as part of the home furniture. Found at http://destiladera.blogspot.com.es/
[i] ATECOS project, Technical Assistant to Sustainable Construction (Asistente Técnico para la Construcción Sostenible) was developed by Miliarium.com, a project coordinate from the Foundation of the Universidad Autónoma de Madrid and the Entorno Foundation, acting as promoter entities, during 2010, 2011 and 2012. In Soluciones en ATECOS a complete list of incorporated Solutions is available aiming to contribute to Sustainable Construction and Energetic Efficiency.
[ii] Jan Pokorný, Jakub Brom, Jan Cermák et al., 2010. Solar energy dissipation and temperature control by water and plants.
[iii] La Association Climatologique de la Moyenne-Garonne et du Sud-Ouest (ACMG) works on knowledge of climate conditions and adaptation to climate change. It has an agro-climatological network in Media-Garonne with 92 posts that provide with information on weather forecasts, assistance to frosts, water management and with technical support to the irrigators’ community. In ADAPTACLIMA II project, ACMG takes responsibility for the pilot project named Optimization of thermal comfort through the use of renewable resources
[iv] Local Scenarios of Climate Change in Andalusia. Environmental Information Network (Red de Información Ambiental (REDIAM) Regional Ministry of Environment and Spatial Planning (Consejería de Medio Ambiente y Ordenación Territorial). Junta de Andalucía. .
[v] Estimation at a detail scale on climate control needs for Andalusia in the context of Climate Change. PhD thesis by Javier Marzo Artigas, supervised by Dr. María Fernanda Pita López, which aim is the estimation of time-space variations suffered by climate control (warming and cooling) in Andalusia in the context of climate change.