Heat build-up lesser in chaotically arranged cities: Study

New York: Researchers have found that heat build-up gets lesser in cities where streets and buildings are arranged chaotically compared to those cities laid out in a more ordered way.

The researchers determined the patterns of buildings from satellite images of 47 cities around the world.

The findings, published in the journal Physical Review Letters, suggest that arrangement of a city's streets and buildings plays a crucial role in the local urban heat island effect, which causes cities to be hotter than their surroundings.

The heat island effect has been known for decades. It essentially results from the fact that urban building materials, such as concrete and asphalt, can absorb heat during the day and radiate it back at night, much more than areas covered with vegetation do. 

The new finding could provide city planners and officials with new ways to influence those effects.

In hot locations, cities could be designed to minimize the extra heating, but in colder places, the effect might actually be an advantage, and cities could be designed accordingly.

"If you're planning a new section of Phoenix (a city in Arizona, US), you don't want to build on a grid, since it's already a very hot place. But somewhere in Canada, a mayor may say no, we'll choose to use the grid, to keep the city warmer," said one of the researchers Roland Pellenq from Massachusetts Institute of Technology (MIT). 

The researchers found that some cities, such as New York and Chicago, are laid out on a precise grid, like the atoms in a crystal, while others such as Boston or London are arranged more chaotically, like the disordered atoms in a liquid or glass. 

The "crystalline" cities had a far greater build-up of heat compared to their surroundings than did the "glass-like" ones, the study said. 

The study found these differences in city patterns was the most important determinant of a city's heat island effect. 

The differences in the heating effect seem to result from the way buildings reradiate heat that can then be reabsorbed by other buildings that face them directly, the team determined.