Athens

Greece

Mission city Twin city
Greece National Platform
Athens Mission City Label
Population 3.6 million
City Area 427 km²
City active since June 2022

Athens Metropolitan Area (Greek: Αθήνα, romanised: Athína [aˈθina]) is where the capital city of Greece is located. With a population close to 4 million, it is the largest metropolitan area in Greece and the seventh largest in the European Union. The City of Athens forms a small administrative unit within the wider metropolitan region, with a population of 643,452 (in 2021) within its official limits and a land area of 38.96 km².

 

Athens is one of the world’s oldest cities, with a recorded history spanning more than 3,400 years and human presence dating back somewhere between the 11th and 7th millennia BC. Classical Athens was a powerful city-state and a centre for the arts, learning, and philosophy, home to Plato’s Academy and Aristotle’s Lyceum. It is widely referred to as the cradle of Western civilisation and the birthplace of democracy, largely because of its cultural and political influence across Europe, particularly Ancient Rome.

 

Today, Athens is a large cosmopolitan metropolis and a hub for Greece’s economic, financial, industrial, maritime, political, and cultural life. In 2021, its urban area hosted more than 3.5 million people—around 34% of Greece’s total population. It is also a major tourist destination, drawing millions of visitors each year. Athens is classified as a Beta global city by the Globalization and World Cities Research Network and is one of the biggest economic centres in Southeastern Europe. It has a substantial financial sector, and its port, Piraeus, is the largest passenger port in Europe and the third largest in the world.

Key Learnings

Concept: Urban heat island effect mitigation - Greenery

The heat island phenomenon rises the temperature of cities, increases the energy demand for cooling and deteriorates comfort conditions in the urban environment. To counterbalance the impact of the phenomenon, important mitigation techniques have been proposed and developed.     It is widely accepted that an increase of the urban green infrastructure, and particularly of the tree cover, improves urban resilience [1-2]. Trees provide urban overheating reduction, pollutant removal, carbon sequestration, retention and detention of storm water runoff, while improving residents’ health [3-8]. The American Forestry Association in 1989 estimated that the value of an urban tree is close to $57,000 for a 50 years mature specimen. This value includes the benefits for air conditioning, soil protection, air pollution and wildlife habitats (9).  The present fact sheet aims to provide information and recommendation on the impact of urban greenery on the urban climate and in particular on the potential decrease of the urban overheating. It does not discuss the impact of urban greenery on the specific energy demand of buildings. The fact sheet considers four types of urban greenery: Urban parks, street parks, green roofs and vertical green infrastructure attached to buildings.    Greenery contributes to decreasing the ambient temperature through evapotranspiration and shading. In parallel, when impervious surfaces like asphalt and concrete are replaced by vegetation, the stored heat during the day and the emitted sensible heat during the day and night are significantly reduced. The potential temperature decrease because of the increased green infrastructure fraction depends on the difference of the thermal balance between the non-vegetated control/reference scenario and the vegetated one. It is mainly affected by the specific climatic conditions, the availability of soil moisture, the type of vegetation and the way it is distributed in a city. As a result, increased vegetation fractions may contribute to reducing the ambient temperature during the night or the day or both, or even cause some warming effects under specific conditions.  To increase the urban green infrastructure, additional trees placed in urban parks or streets as well as building integrated greenery like planted roofs and vertical greenery systems may be used.   Urban Parks  Figure 2 : Bergpark Wilhelmsshohe Germany. Picture from : Bergpark Wilhelmshöhe - Urban Park in Germany - Thousand Wonders.     Green roofs are partially or completely covered by plants over an engineered planting substrate on specialized build up of polymer materials. They are differentiated by the type of plants they may support. Extensive type green roofs are covered by low vegetation while intensive green roofs may support growing of shrubs and small trees. Important benefits are associated with the use of green roofs. Because of the solar and heat protection they provide, they contribute to lowering the energy consumption of buildings, while through latent heat processes, they decrease the surface temperature of the roofs and reduce the release of sensible heat to the atmosphere. In parallel, green roofs help with the storm water runoff management, provide better air quality, reduce noise, prevent erosion and increase the durability of the roof materials (10).  Green Roofs  Figure 3 : Green Roof in Athens, (9)    There is an acceptable correlation between additional tree cover and the ambient temperature drop during the peak day period and at night. The average maximum drop of the peak daily temperature may not exceed 1.8 ◦C, when the tree fraction reaches its maximum, while the average night-time maximum mitigation potential is much higher and close to 2.3 ◦C. Given the serious spatial limitations in cities, a potential increase of the tree cover by 20% may initiate a temperature decrease close to 0.3 and 0.5 ◦C during the daytime and night-time, respectively.  The local landscape and climate conditions highly affect the potential temperature drop in a city; however, the order of magnitude of the temperature drop remains close to the previously mentioned levels. Given that most of the cooling demand is during the peak daytime period, the shift of the maximum mitigation potential of trees during the night reduces the expected cooling contribution. Potential problems of night warming and serious increase of humidity levels reported by numerous studies should not be neglected, especially when additional trees are deployed in urban canyons, reducing the sky view factor, and when additional green infrastructure is planned in humid climates.  There is a statistically significant correlation between the peak daily temperature decrease caused by higher green infrastructure fractions and heat-related mortality. When the peak daily temperature drops by 0.1 ◦C, then the percentage of heat-related mortality decreases on average by 3.0%  Urban greenery and in particular trees contribute seriously to urban cooling 10 to 15 years after plantation. However, urban trees and the rest of the urban greenery systems present a very long-life span and may contribute to urban cooling for more than 30-50 years.   Street Trees  Figure 4: Street Trees. Picture is taken from : 20 Incredible Benefits of Urban Street Trees (arbor1.com).   Vertical Greening  Figure 5 : Vertical Greening in Volksbank Austria. Picture is taken from: Green Buildings - Volksbank Blog.   Several European cities increase the percentage of urban green infrastructure to improve the urban microclimate. The greenness of European cities has increased by 38% over the last 25 years, with 44% of Europe’s urban population currently living within 300 metres of a public park, (11). On average, some 40% of the surface area of European cities is made up of urban green infrastructure, with around 18.2 m2 of publicly accessible green space per inhabitant, (11). Figure 1, gives the available public green space per inhabitant in Europe, (12).  Figure 1. The available public green in European cities per inhabitant, (12)    MATURITY:  Urban Greenery is the most mature mitigation measure that supports the improvement of the urban microclimate and counterbalances the impact of urban overheating.   Especially green roofs are extremely well developed, matured, commercial greenery system, available to the market. Green roofs are tested under all climatic conditions, and they provide a considerable contribution to decrease urban overheating.  

Concept: Urban heat island effect mitigation - Cool urban surfaces (reflective) 

The heat island phenomenon raises the temperature of cities, increases the energy demand for cooling and deteriorates comfort conditions in the urban environment. To counterbalance the impact of the phenomenon, important mitigation techniques have been proposed and developed. Absorption of solar radiation by the materials of the building envelope and the city structure contribute to increasing urban overheating. Use of solar reflective materials, known as cool materials, helps to decrease the surface temperature by up to 20 °C and the ambient urban temperature by up to 2 °C (1). In parallel, it can contribute to decreasing the cooling load of buildings by up to 40 %, the peak indoor summer temperature by up to 5-6 °C, the concentration of harmful pollutants and in particular of ground level ozone, and the heat related mortality and morbidity, all the while improving indoor and outdoor thermal comfort (2).  Reflective, cool materials present a high reflectance to solar radiation combined with a high emissivity factor, thus these materials do not absorb much and can easily lose the stored energy. White materials present a high reflectivity that can reach 0.95 both in the visual and infrared solar spectrum; however, also coloured reflective materials exist that present a high reflectance in the infrared part of the solar spectrum, to cater to different users’ needs and local architectural requirements (3).   Cool materials can be used either on the envelope of the buildings, as cool roofs or in the urban structures as cool pavements and cool streets. When applied on roofs, materials of very high reflectivity can be used. However, when used on vertical surfaces, pavements and streets, reflectivity should not exceed 50 %, to avoid problems of glare and contrast. In Europe, most of the cool materials are accredited and their performance is certified by the European Cool Rood Council. A list of the certified materials can be found in (4). The various types of existing cool materials for buildings and pavements can be found in (1,5). Examples of successful projects, as well as data on the accredited materials and other useful information on reflective materials can be found in the final report of the Cool roofs council project of EU (6).  COOL ROOFS Surface temperature differences before and after the cool roof application as depicted by an infrared camera for the Athens case study.  Source: (6)  Visual and thermal images of the roof of an industrial building in the Netherlandsbefore the cool material application (7)  Visual and thermal images of the roof of an industrial building in the Netherlands after the cool material application, (7)    LONGEVITY and REUSABILITY  Cool materials present similar mechanical properties as the conventional ones. Optical ageing of cool materials can be a significant problem especially for the non-certified products. Information on the long-term reflectance of cool materials is provided for all certified products by the European Cool Roof Council (4). The use of materials presenting a minimum loss of solar reflectance is highly recommended. When paints or coatings are used, water-based materials containing zero or minimum VOCs have to be selected.   COOL PAVEMENTS  Surface temperature of the Cool shaded, (AR01), the conventional non-shaded, (AR02), and the cool non-shaded pavement, (AR03) In the Floisvos urban Rehabilitation project. .  Source (8)  Reflective Cool asphalt in Athens. Source (9)    RECYCLABILITY and NEW MATERIALS  Ceramic, asphalt, or concrete based cool materials can be recycled as any other conventional material of the same nature. Especially concrete pavements should be fully recycled and reused as a filling material for new pavements or other building processes. Most of the used cool membranes can be also fully recycled.  MATURITY:  Cool Roof Technologies and Cool pavement products are available and can be used on a commercial basis.   Advanced super cool materials presenting sub ambient surface temperature will be available for commercial deployment by 2023.  

PRODESA - Energy efficiency in Greek municipal buildings

PRODESA aims to assist 7 municipalities in Athens Metropolitan Area to begin energy efficiency and renewable energy projects, using innovative financial tools and attracting private investments. PROSPECT+ fosters capacity building in regional and local authorities in order to finance and implement effective and efficient sustainable energy plans, including their proper monitoring and verification. https://www.h2020prospect.eu
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Pilot project spotlight

Athens Pilot Activity: ASCEND
Background The ASCEND pilot activity aims to address key challenges in the local context, focusing on climate commitments and urban sustainability. Athens faces issues such as air and noise pollution, energy poverty, and unequal access to urban amenities, particularly
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