Extensive urbanization has resulted to economic, social, energy &
environmental challenges. The global population increase led to an increasing demand
for housing. Natural land has been replaced with artificial surfaces in most cities around
the world with undesirable thermal effects. This, together with industrialization growth,
has caused a deterioration of the urban environment. Urban heat island (UHI)
phenomenon has become a common problem in many major cities worldwide. Several
factors influence the urban heat island phenomenon, such as the continuous reduction of
green spaces, the changes of wind velocity due to high buildings’ density, the
anthropogenic heat release and the alteration of surfaces’ albedo. The aforementioned
factors lead to overheating problems in cities due to the absorption of solar radiation by
the various surfaces and buildings. Hence, urban climate is one of the most important
elements of urban physical environment, which is often ignored in urban planning. To
design a sustainable city, it is necessary to take into account the climatic conditions
holistically and strategically during the planning process. Since the 1970s, German
researchers have developed the concept of urban climate map (UC-Map) that has a
strong focus on applied urban climatology. UC-Map is an appropriate tool for
translating climatic phenomena and problems into 2-D images including symbols for
land use and spatial information suitable for the urban planner. Therefore this map is a
useful tool for urban planners, architects and governors in order for them to understand
more accurately and evaluate the effects of urban climatic issues on decision-making
and environmental control. At the micro-climate level, several UHI mitigations can be
implemented to reduce the UHI severity. First is greenery. The benefits of greenery to
the built environment have been widely investigated. Greenery dissipates the incoming
solar radiation on the building structures through its effective shading; it reduces longwave
radiation exchange between buildings due to the low surface temperatures created
by plants’ shading; it reduces the ambient air temperature through evapotranspiration.
The role of building’s materials, mainly determined by their optical and thermal
characteristics, is crucial in reducing the thermal and solar hear gains, in the urban
environment. The so-called ‘cool’ materials, characterized by high reflectivity and high
emissivity, can improve the thermal conditions in cities by lowering the surface
temperatures that affect the thermal exchanges with the surrounding air. Urban ventilation is another important strategy of UHI mitigation. It is important to understand
the nature of air flow regimes within urban canyons in order to make further progress in
describing the complex interactions between mesoscale forces and the built
environment that create the urban boundary layer.
Keywords: Urban heat island, mitigation strategies, urban climatic map, urban
greenery, urban ventilation, cool materials.
