Where are the warmest and the coolest places in Montreal?

Summer means heat waves, and cities can get unbearably hot thanks to the urban heat island effect. The concentration of asphalt and concrete traps in heat, making urban centres significantly hotter than natural areas.

It's easy to see on a map. TheSatellite readings from CERFO, a forestry research centre in Ste-Foy, Que., clearly shows which parts of Montreal are hotter relative to others.

The good news is that there are plenty of spots to escape the hot days.

Here are 13sectors across the Island of Montreal that are both cool, and offer a vast swath of trees and activities during the hot summer months.

See a larger version of the map here

A quick warning: the map does not show exact temperatures, only relative differences. One cannot say, for example, that it's 32 C in a red zone or 25 C in a blue one.

AngrignonPark

3400 Blvd.des Trinitaires

BoisdeSaraguayNature Park

9150GouinBlvd. West,Cartierville

Cap Saint-Jacques

20800GouinBlvd. W.,Pierrefonds

De laPromenade-BellerivePark

9200 Notre-DameBlvd. E.

JarryPark

St-Laurent Boulevard,Villeray

La Fontaine Park

Sherbooke Street East

Mackenzie-King Park

4955Cte-des-NeigesBlvd.

Mount Royal Park

Avenue du Parc

Pointe-aux-Prairies

14912 Notre-Dame Blvd.E.,Rivire des Prairies

Pie-XII Park

5217LavoisierBlvd., Saint-Lonard

Quai-de-LaTortuePark

LaSalleBoulevard, Verdun

Terra-Cotta Park

204 Belmont Ave.,Pointe-Claire

WilliamCosgroveCentennial Park

3000Lake St.,Dollard-des-Ormeaux

Why is it so warm in the city?

The urban heat island effect is caused mainly by three features of cities:

• Low tree cover.
• Dark materials, like tar and asphalt that absorb sun rays and radiate heat.
• "Canyons" created by tall buildings that trap in heat.

Roofs made from dark materials and streets can reach temperatures as high as 80 C during very warm days, according to a report from the Institut national de sant publique du Qubec.

Montreal can sometimes be 12 degrees warmer than surrounding rural areas due to a combination of these factors.

The number of days of extreme heat is also expected to spike due to climate changes, according to Natural Resources Canada. In Montreal, there are about nine days per year where the temperature is above 30 C. Natural Resources Canada predicts that by 2070, there could be as many as 27 days where the temperature breaks 30 C.

What can be done to reduce heat in urban centres?

There are many ways to mitigate heat islands. These include:

• Planting more trees.
• Adding vegetation to parking lots.
• Paving roads with light-coloured material.
• Covering building walls with plants like ivy.
• Green roofs or replacing dark roof material with light or reflective surfaces.
• Turning more alleys into green alleys (12 boroughs have specific plans on this).

Methodology

The temperature map was created using data from CERFO, which usedimages from the SPOT-5 satellite and surface temperature readings from the Landsat-7 satellite. A total of 67 images were collected over six years, always during the summer months.

CERFO developed a mathematical model to combine surface temperatures from low resolution readings (100x100 metres per pixel) onto high resolution images without thermal data (20 metres).

The map does not show absolute temperatures, but relative temperatures in urban areas.

The prediction model has a margin of error between the real and predicted temperature. The overall accuracy was assessed at 67 per cent. CERFO believes that this margin of error of 33 per centis satisfactory given the extent of the territory analyzed (all of urban Quebec), which has a wide variety of terrains, such as Montreal and Gasp.

The data is published in the Quebec government's open data portal.