Summary:
Urbanization and increased urban density impact negatively the thermal
environment as cities in an urban environment change dramatically the local
climate. A typical example of urban climate change is the urban heat island
effect that appears in many European cities. Urban Heat Island (UHI) effect is
a phenomenon in which air temperatures in densely built urban areas are higher
than the temperatures of the surrounding rural areas.Moreover the burden of
urban thermal environment is a matter of first priority as it affects the
quality of urban residents’ life but also leads to an increase in energy
consumption for cooling. Additionally a city with overburdened thermal
environment causes an increase in emissions of greenhouse gases that affects
the broader problem of global climate change. Expecting a quick and massive
population growth in the near future, the implementation of mitigation and
adaptation measures to the phenomenon of urban heat island effect may be
necessary to reduce energy consumption and to have a better quality of life in
cities.The most important initiative to address climate change and turn society
into a more sustainable urban development model in the European Union is the
Covenant of Mayors. This pact is backed by local master plans specifying
priorities and measures per city.
Firstly the causes and impacts of urban heat islandswill be discussed. The
emergence and intensification of urban heat islands are promoted by the local
climate, which is influenced by various meteorological parameterssuch as
temperature, relative humidity and wind and a number of anthropogenic
causes.These causes are the local climate, theanthropogenic activities, the
gradual loss of urban forest cover and the impermeability and low albedo
ofmaterials, the thermal properties of materials, urban morphology and the size
of cities.During the summer, urban heat islands can have adverse impacts on the
environment andon health. The impacts of urban heat islands on environment are
an increase in energy demand, a deterioration of air qualityand anincrease in
demand for potable water. On the other hand the impacts of urban heat islands
on health are an increase in mortality rates and diseases.
Afterwards the quality of Athens’ thermal environment will be analyzed, in this
paper. The city of Athens is characterized by a strong heat island effect,
mainlycaused by accelerated industrialization and urbanization during recent
years. Thisphenomenon is mainly influenced and affected by the atmospheric
circulation whichis responsible for the formation and evolution of the
meteorological elements thatcan enforce or eliminate the phenomenon. Athens is
the capital of Greece and the biggest city of Greece.The climate of the area is
Mediterranean with hot, dry summers and wet, mild winters. The local winds in
the Basin of Attica blow mainly along the axis N-NE / S-SW with prevailing wind
direction to the NNE in the summer, autumn and winter and the SSW in the spring
and early summer. The solar radiation is high and itis an important factor for
the estimation of urban heat island, and represents the amount of energy that
reaches the earth's surface as direct and diffuse radiation. Last but not least
air pollutants will be studiedbecause of the fact that one of the most serious
problems that face Athens and generally urban areas are the concentrations of
air pollutants.
In the last decade, international and European efforts have been mainly focused
on mitigation and adaptation strategies. These strategies differ from each
country according both to medium- and long-term adaptation needs and developing
and implementing strategies and programmes to address those needs.
Theadaptation plans of other European cities which are London, Rotterdam and
Copenhagen will be examined, in order to reduce the urban heat island effect
and inform citizens. These three cities are chosen because they are actively
engaged in both mitigation and adaptation issues. Their strategies are
addressed not only to prevent or reduce the impact of the numerous risks
associated with climate, but, above all, to maintain and improve the quality of
life and well-being for the present and future generations, and to protect and
improve the quality of the urban environment.
As Athens developed rapidly, green surfaces are replaced with imperviousones.
These hard surfaces with commercial and industrial uses, dense traffic and high
population size in the city produce high amount of heat. In order to reduce the
intensity of urban heat island effect in Athens and the city will become more
thermal resilient, strategies for building and urban scales are developed based
on the literature review. These strategies are using more green elements,
albedo materials in the city and on the building’s vertical and horizontal
sections and they have a goal to decreaseanthropogenic heat and air
pollution.To be more specific the strategies are divided into four areas that
are: albedo, an urban greening, ventilation and environmental management. For
the evaluation of the adaptation plan is necessary to monitor the
implementation of measures with the help of indices and draft reports that will
indicate the best practices. The results of such monitoring provide important
information such as the identification of successful measures and of course
contribute to monitor the impact of the phenomenon of urban heat island and
improve the policy measures.
Finally the relationship between urban heat island effect and heat wave effect
will be examined. Heat waves are excessively hot periods during which the air
temperatures of both urban andrural areas increase significantly. This
relationship during the summer months is bidirectional. Not only do the heat
wavesintensify the urban heat island effect, but also the urban heat island
effect intensifies the heat waves. As a result, the added heat stress in cities
will be even higher and residents’ health will be affected. So a National Plan
for heat waves should be designed. The plan should specify the responsibilities
of each institution at national and local level for preparation of extreme
weather conditions during summer and prevent diseases that are associated with
the increase of temperature and warn individuals and organizations when the
heat waves are predicted.
Keywords:
Urban Heat Island, Athens, Mitigation, Adaptation Strategies, Thermal Environment.
