The green roof of the Ministry of Economics and Finance
: One of the main aims of this initiative was to furnish a research roof to evaluate the thermodynamic effect of a green roof in hot Athens. Two studies of the thermodynamics of the roof were carried out (in September 2008 and August 2009), which concluded that the thermal performance of the building was significantly impacted by the installation. Energy savings of 50% were noted for air conditioning on the floor directly under the installation. The ten-floor building has a total floor area of 1.4 hectares. The green roof is spread over 650 m2, equalling 52% of the roof space and 8% of the total floor space. Despite this limited area, energy savings adding up to €5,630 per annum were recorded, which translates to a 9% saving in air conditioning and a 4% saving in heating costs for the whole building. The research established that both the micro-climate and biodiversity of Constitution Square, in Athens, Greece had been ameliorated. Athens, like the rest of Greece generally, is a hotspot of seismic activity, so one of the principal limitations of this installation was an acceptable load. The wet weight of the build-up is under 50 kg/m2. The lightweight was achieved by incorporating an array of strategies, including shallow substrate depth (under 10 cm) and lightweight substrates. While an elevated water storage capacity would be a plus for roofs in dry Athens, weight considerations precluded this from being viable.
Moreover, summer irrigation was considered to be undesirable so the plant range was also restricted. Primarily, local native species were planted. (IUCN, 2019).
Reduced drought risk, cooling effect, urban heat island mitigation
Yes, studies of the thermodynamics of the roof in September 2008 and further studies in August 2009 proved that micro-climate of Constitution Square (Syntagma Square, considered the most important square of modern Athens from both a historical and social point of view, is located at the epicentre of commercial activity and Greek politics), in Athens was significantly affected by the installation of the oikostegi. An additional observation and conclusion of the study was that the thermodynamic performance of the oikostegi had improved as biomass was added over the 12 months between the first and second study. This suggests that further improvements will be observed as the biomass increases still further. (IUCN, 2019).
Biodiversity conservation or increased biodiversity
Mainly local species were chosen so as to be able to survive the harsh conditions of this particular roof. The plant selection was mainly composed of native Hellenic aromatic herbs such as several species of thyme, sage, lavender, mint and oregano as well as marjoram and savoury. Studies of the thermodynamics of the roof carried out in September 2008 and further studies carried out in August 2009 found that, while measurements were being made by thermal cameras, a plethora of birds and beneficial insects were noted on the roof, ranging from robins, yellow hammers, yellow tits, coal tits, and sparrows to kestrels hovering high above eyeing up the smaller birds. Several species of pollinators were noted such as honey bees, tiger swallowtail and monarch butterflies, together with dragonflies and ladybugs. Obviously this was not the case before installation of the green roof. (IUCN, 2019).
Increased quality and quantity of green and blue infrastructures
The main aim of for this project was to boost the green infrastructure in the hot city of Athens (IUCN, 2019), due to the fact that green spaces in the densely built-up Municipality of Athens (i.e. the urban historical core of the city), barely cover an area of 0.4 km², which corresponds to just 2.8–3% of the municipality’s surface area. This consequently means that each citizen in the Athens Municipality has access to a mere 2–2.5 m² of green space. At the same time, even if all open spaces (i.e. derelict and underused spaces) in the same area were converted to green areas, this value would only increase to 3.84 m² per inhabitant. (Papageorgiou, Gemenetzi, 2018).
Yes, enhancing natural capital in the metropolitan area. A green roof improves human comfort - by reducing heat transfer through the building roof, it can improve indoor comfort, and lower the incidence of heat stress associated with heat waves. (United States Environmental Protection Agency, 2019). A green roof may also be of help in the development of programmes for promoting “hazard-resistant landscaping” by planting indigenous species, that tend to do well when faced with the harsh conditions prevalent on such roofs. Biophilic urbanism can aid in safeguarding or consolidating favorable climatic and micro-climatic conditions in cities. The power and worth of biophilic urbanism as an urban resilience and sustainability strategy is evident, and several cities have developed and are putting into effect advanced programmes for expanding the nature within and around their territories (Beatley, Newman, 2013; Hazard Resistant Landscaping, (s.a.). Green infrastructure, as a NbS, is particularly vital for metropolitan areas like Athens due to the excessive urban sprawl and population density. Green urban areas also act as air-cleaning filters, ameliorate the microclimate, strengthen biological diversity, reduce city noise levels and other nuisances, lower the risk of floods, function as leisure and recreation venues for social interaction, and aid in upgrading the urban landscape (Papageorgiou, Gemenetzi, 2018).
Improved aesthetic value
Yes, green roofs provide aesthetic value in the built environment. (United States Environmental Protection Agency, 2019). This green roof was installed on the Treasury in Constitution Square in Athens (on top of the building housing the Greek Ministry of Finance), which is considered the pre-eminent square of modern Athens from both a historical and social viewpoint. (IUCN, 2019).
Increased access to green infrastructure
Yes, provision of green space for the enjoyment and reconnection of staff, visitors and public with nature, by supporting urban biodiversity.
Increased social interaction and inclusion
Yes, the green roof provides an opportunity for enjoyment and reconnection for both staff and visitors.
Low air quality
In Athens, two kinds of air pollution have been identified: the first is characterised by high concentrations of particles. The second type - photochemical smog - is linked to an excess of nitrogen oxides, hydrocarbons, carbon monoxide (primary pollutants), ozone, and organic nitrates (secondary pollutants) and is caused by a series of chemical reactions driven by sunlight. (European Environment Agency, 2016).
Drought and heat risk
Vulnerability to heat waves (HWs) is expected to increase in urban environments mainly due to population density and the effect of the urban heat island (UHI) that make cities hotter than surrounding non-urban areas. The coastal city of Athens is highlighted as one of the regions with prominent increase in the frequency, intensity and length of HWs in the present and future climate (Katavoutas, Founda, 2019a). The city has experienced increasing trends in air temperature and heat wave frequency, especially since the mid-1970s. The annual number of days with maximum air temperature above 35°C is increasing, and so is the number of days with extreme heat stress. Heat stress is not determined by air temperature only. Other parameters, like humidity, wind speed and insulation, also determine how we experience a hot day. These parameters can be combined into heat stress indices that, better than temperature alone, reflect thermal comfort. The results show that the population of Athens is exposed to a significant, increasing risk of heat stress since the 1960s, which is maximized in the last two decades. This increase, expressed in the additional time per year that the inhabitants of Athens are exposed to conditions of extreme heat stress, varies from 0.3%/decade to 0.9%/decade, depending on the index. Despite this statistically significant trend over the entire study period, a decline is observed during the last decade. Also during the night-time hours, when the human body should cool down, the population has been exposed to significantly higher heat stress levels in recent decades compared to the past ones. In fact, the time people are exposed to high heat stress has increased at a faster rate for night-time than for daytime conditions. The increase in the time per year of high heat stress conditions results from trends in the timing of heat stress conditions. The occurrence of the first heat stress conditions has shifted to earlier in the year. The occurrence of the last heat stress conditions has shifted to later in the year. As a result, the period of heat exposure has expanded. (Katavoutas, Founda, 2019b; ClimateChangePost, 2020)
Low availability of green infrastructure
Yes, the main observation is that in the wider Athens area the majority of the population and of the built-up area is concentrated in the central urban quarters and their immediate surroundings. The Athens urban area continues to be among the most dense in the developed world. The 2020 edition of Demographia World Urban Areas lists the Athens urban area as having a population of 3.332 million, spread across a land area of 584 square kilometers, amounting to a density of 5,706 per square kilometer. (Demographia, 2020).
Good health and well-being (SDG3)
Sustainable cities and communities (SDG11)
Climate action, resilience, mitigation and adaptation (SDG13)
IUCN. 2019. Nature based Solutions in Mediterranean cities. Rapid assessment report and compilation of urban interventions (2017‐2018). Malaga, Spain: IUCN. 117pp. Katavoutas, G., Founda, D. 2019a. Response of Urban Heat Stress to Heat Waves in Athens (1960–2017). Atmosphere, 10, pp. 483-499. https://doi.org/10.3390/atmos10090483.
Katavoutas G, Founda D. 2019b. Intensification of thermal risk in Mediterranean climates: evidence from the comparison of rational and simple indices. International Journal of Biometeorology, 63(9), pp. 1251-1264. https://doi.org/10.1007/s00484-019-01742-w.
Papageorgiou M, Gemenetzi G. 2018. Setting the grounds for the Green Infrastructure in the metropolitan areas of Athens and Thessaloniki: the role of green space. European Journal of Environmental Sciences, 8(1), pp. 83-92. https://doi.org/10.14712/23361964.2018.12.