Banking on air-conditioners to provide respite from the sweltering heat? You could be contributing to the creation of a ‘heat island’. A new climate model of Abu Dhabi can help mitigate the urban phenomenon
Urban Heat Islands
The US Environmental Protection Agency describes heat islands as “built-up areas that are hotter than nearby rural areas”. On an average the annual air temperature of a heat island in a city with 1 million people or more can be 1–3°C warmer than its surroundings. In the evening, the difference can be as high as 12°C. Heat islands can affect communities by increasing summertime energy demands, air-conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality.
When cities undergo urbanisation, a vast amount of energy or heat is generated. This could be from gases released from vehicles, heat trapped in pavements which radiates back into the environment, or heat absorbed by multi-storey buildings, which once again is ejected into the atmosphere. But the primary cause of the creation of heat islands is the use of air-conditioners.
The effects of a heat island can be reduced by developing efficient cooling systems, adding vegetation to buildings, cooling paved surfaces with reflective paint etc.
Cold facts — a vicious cycle
As the temperature outside increases, the demand for cooling devices like air-conditioners also rises. These devices emit heat-trapping greenhouse gases into the atmosphere, which further increases the temperature of the area. This once again triggers the need for more cooling devices, leading to a vicious cycle. Reducing the cooling load of a city would not only prevent the creation of hot zones like heat islands, it would also reduce a city’s carbon footprint, and help achieve a low-carbon, sustainable, and resource-efficient future.
The new model
The energy expense for air-conditioning currently accounts for 60 per cent of annual and 75 per cent of peak-day electricity use in Abu Dhabi, the second most populous city in the UAE. The temperature in the summer months crosses 40°C on most days. The Abu Dhabi skyline is dotted with modern towers and air-conditioned shopping centers — structures that researchers believe have been contributing to the heat island effect in the city for years. It was with this in mind that researchers from the Massachusetts Institute of Technology, US, and Masdar Institute of Science and Technology in Abu Dhabi collaborated, to develop a 3D climate model of Abu Dhabi’s downtown area, to help minimise effects of the heat island.
The computational model describes the flow of heat between buildings — how heat released from the cooling devices of one building was absorbed by the neighbouring structure, increasing temperatures. For the model, the research team collected data from local weather stations. With the help of this information, the model calculated air temperature, wind speed and solar radiation, building facade and ground temperature in the Abu Dhabi downtown area. To understand the geographical structure of the city, the researchers used data from Abu Dhabi’s geographical information systems (GIS). With the help of this data, the researchers could calculate the cooling demands of each building in the area individually. The 3D model helped measure the heat ejected by the cooling devices. The researchers also calculated the heat emitted by motorised traffic. Finally, they integrated all the information to get an accurate picture of heat flow through the region.
How will the new model help?
The researchers are now building in-house weather sensors that will be placed across Abu Dhabi city. The researchers say this will provide them with better and more accurate data and help calibrate the model. Once completely ready, the model can help in tackling the heat island effect in the city and can be used by other countries too to mitigate the effect. Cities like Tokyo have been struggling to cope with the phenomenon as well.
“This model will be a tool for city managers and planners to conduct simulation-aided design of Abu Dhabi’s downtown, showing them how the construction of an additional building, park, street, or other infrastructure will impact the urban heat flow,” Prashanth Marpu, Masdar Institute’s principal investigator on the project, told US-based Electronic Component News magazine.
The new model will also help urban planners weigh different design scenarios for buildings and develop ‘shading strategies’ that will be most suitable in reversing the heat island effect. In the long run, the model can help reduce the energy costs and carbon foot print of a city.