Gulf Times
Doha, Apr 13: HIGH-RISE buildings might be seen as signs of modernity and development, but they could be detrimental to the environment and human health.
High-rise structures, as those coming up in Doha’s West Bay area, cause urban heat islands (UHI). They “create areas which are significantly warmer than their surroundings”, said Dr Tapas Kumar Bandyopadhyay, senior environmental specialist at the Supreme Council for Environment and Natural Reserves (SCENR).
High-rise buildings could have a negative impact on the environment and human health. Picture: Jayan Orma
The temperature difference is usually larger at night than during the day and larger in winter than in summer, said Bandyopadhyay, who has done his masters and doctorate from the Indian Institute of Technology, Delhi.
The temperature difference is most apparent when winds are weak, the specialist said.
The main cause of the urban heat island is also modification of the land surface by urban development. Waste heat generated by energy usage is a secondary contributor. As population centres grow they tend to modify greater areas of land and have a corresponding increase in average temperature.
The principal reason for the night-time warming is the comparatively warmer buildings blocking the view to the relatively colder night sky. Two other reasons are changes in the thermal properties of surface materials and lack of ‘evapotranspiration’ in urban areas, he said.
Materials commonly used in urban areas, such as concrete and asphalt, have significantly different thermal bulk properties and surface radiative properties than the surrounding rural areas.
This causes a change in the energy balance of the urban area, often leading to higher temperatures than surrounding rural areas.
The energy balance is also affected by the lack of vegetation in urban areas, which inhibits cooling by ‘evapotranspiration’.
“Heat islands form as vegetation is replaced by asphalt and concrete for roads, buildings, and other structures necessary to accommodate growing populations”, Bandyopadhyay said, quoting the Environmental Protection Authority of USA. “These surfaces absorb - rather than reflect - the sun’s heat, causing surface temperatures and overall ambient temperatures to rise.”
UHIs have the potential to directly influence the health and welfare of urban residents, he argued. Within the US alone, an average of 1,000 people die each year due to extreme heat, he said.
As UHIs are characterised by increased temperature, they can potentially increase the magnitude and duration of heat waves within cities, the environmentalist said.
Research has found that the mortality rate during a heat wave increases exponentially within UHIs. The nighttime effect of UHIs can be particularly harmful during a heat wave, as it deprives urban residents of the cool relief found in rural areas during the night, he pointed out.
Aside from the obvious effect on temperature, UHIs can produce secondary effects on local weather conditions, including the altering of wind patterns, the development of clouds and fog, the humidity, and the rates of precipitation.
The heat island effect can be counteracted slightly by using white or reflective materials to build houses, pavements and roads. This is a long established practice in many countries.
A second option is to increase the amount of well-watered vegetation. These two options can be combined with the implementation of “green roofs”, he suggested.
A green roof does not point to its colour but refers to a building that is partially or completely covered with vegetation and soil, or a growing medium, planted over a waterproofing membrane.
Rooftop ponds are another form of green roofs which are used to treat grey water. The term “green roof” might also be used to indicate roofs that use some form of “green” technology, such as solar panels or a photovoltaic module.
“With the mushrooming of high-rise buildings in Doha, the city might experience the UHI effect in future and might have a negative impact on people’s health and on the environment”, he said.