Urban heat island effects depend on city’s layout

WASHINGTON: The 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, a study has found.

Researchers at Massachusetts Institute of Technology in the US 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, they said.

They found that the “crystalline” cities had a far greater buildup of heat compared to their surroundings than did the “glass-like” ones.

The study, published in the journal Physical Review Letters, found these differences in city patterns, which they call “texture,” was the most important determinant of a city’s heat island effect.

The researchers noted that using mathematical models that were developed to analyse atomic structures in materials provides a useful tool, leading to a straightforward formula to describe the way a city’s design would influence its heat-island effect.

“If you are planning a new section of Phoenix, 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 Roland Pellenq from Massachusetts Institute of Technology.

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 researchers determined. PTI