The CMA (Census Metropolitan Area) of Toronto is the biggest metropolitan area in Canada (Statistics Canada, 2007). The area occupied by this CMA is 5903,6 km2. Population in this CMA is the highest in Canada as well : 5 113 449 people (Statistic Canada, 2007).

Source: NASA World Wind, 2007

Heat Islands in this city are a big concern. As a matter of fact, Toronto CMA occupied the second place after Vancouver for their surface and growth between 1985 and 2004. Heat islands occupied 690,05 km2 in 2004.

We define Surface Urban Heat Islands as a temperature at least 5 degrees above the average of the whole city. As a result of this definition, Toronto CMA had in 1985 a 9,84% of its surface 5 degrees or more hotter than his own average. In 2004, Toronto expanded this surface to 12,86%, which means a growth of 3,02%.

The next image shows Toronto urban heats islands (July 18, 1985):

Source : Perez C., 2008

The following map shows the surface temperature (TOA) of Toronto CMA on July 4, 2004. On this day, the averagetemperature was 21,35°C for the whole CMA.

Source : Perez C., 2008

Toronto CMA is currently growing, merging with other smaller cities around it or simply transforming former countryside areas in urban developments. This fast growth is probably accompanied by a lack of vegetation which is replaced by asphalt or cement.

Opposite to this, the downtown of Toronto seems to be cooler than the suburban area. This trend is most likely due to the effect of two factors: vegetation surface on this area has grown or the anisotropy effect of higher buildings are cooling it. Shadows of buildings could be big enough to cool the city. Particulary at 10:30 am when this Landsat 5 image was taken.

Anisotropy effect in the downtown of Toronto

Source : Google earth, 2008

We think that Urban Heat Islands are still growing in Toronto at a high rate (3%). The 160 Km2 taken by heat islands are hard to recover and that depends on the decision of people and politicians.