Urban Heat Islands, why are cities so much hotter than the countryside?

Urban Heat Islands, why are cities so much hotter than the countryside?

Cities make up for just 2% of the total land area of the earth, but currently 55% of the global population lives in them. This number will increase to 80% in the next 40 years. The environment will be greatly affected in terms of energy consumption, pollution levels and water demand.

Urban heat island’s is an area that is significantly hotter than a rural area mainly due to human activities. Temperature difference is larger during night time than during daytime, and it is more apparent when the wind is weak. London has recorded a temperature that is up to 6° C more than surrounding areas. With rapid development in the urban areas, its impact on climate change has become apparent. Many countries worldwide have pledged to reduce temperature to develop a much more sustainable urban landscape.

So, what can cities do to reduce the temperature?

One practical way to achieve this is to design the city buildings in such a way that they will require lesser energy to employ and run passive means to control climate. However, it could be years before these development start to show effects to drive a more sustainable urban development. Hence other solutions also need to be explored.

Black and White solution: The dark surfaces in our cities absorb and release heat. Asphalt and concrete are widely used materials in construction, they are dark colored and have high density which make them store more heat. To combat this LA authorities launched Cool Pavement project. In this, roads are painted white with an asphalt emulsion which helps the roads reflect heat. As of yet the cost of painting is quite high, however sites have recorded a temperature drop of 5.6° C.

Greening of the concrete jungle: Some cities are extensively turning rooftops into urban gardens. Chicago, Toronto, San Francisco, Denver and many other cities in North America have successfully implemented laws to build these rooftop gardens across the city buildings that are more than 2000 sq meters. Engineers and architects have taken further steps to develop structures with entire trees. These structures called as vertical forests have 100s of trees in them. They keep the building’s temperature significantly down.

Masdar city which is located in UAE, it is an urban center which is developed as blueprint for smart city. There are no cars permitted in the proximity of the buildings. There is also a 46 m wind tower which sends cool air down, as a result Masdar is up to 14° C cooler than the nearby areas. This is called as Urban cool island’s effect. Cities across the world are now developing green ventilation corridors which will allow cool air to flow freely without obstacles which will further bring the city’s temperature down.

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