Building Resilience to Climate Change in Human Settlements
Extreme heat in urban environments increases smog production and impacts on public health. The goals of this activity are to contribute earth science information to improve understanding of urban heat island effects, and to support the development of effective planning strategies related to environmental degradation and energy consumption within the context of a warming climate.
Leader: Matthew Maloley
The Topic
Urban centres can be especially susceptible to extreme heat events due to the urban heat island (UHI) effect. Urban centres tend to have higher air temperatures, particularly at night, than surrounding rural areas. This is due to a city's lack of vegetated areas, the heat absorbing materials used for buildings and infrastructure (i.e. concrete, asphalt), and multi-story structures which further trap heat.
Through the mapping of heat island variations, planners can be provided information to adapt to extreme heat events, such as placing cooling centres or emergency services in high heat/high vulnerability neighborhoods. Urban heat island mapping can also advise municipalities on the impacts of urban developments, and guide policies (i.e. green roofs) to adapt to both continued urbanization and rising temperatures.
This activity works with decision-makers in the City of Toronto to identify and characterize urban heat island impacts in order to help develop adaptation options that reduce and respond to extreme summer heat. This activity will use integrated urban geospatial information to predict intra-urban heat island variations across the Greater Toronto Area.
Results
Air temperature and surface temperature measurements were collected from a variety of sources to characterize the microclimatology across the Greater Toronto area. Land cover maps were also produced to establish links between surface cover types and temperature regimes.
Satellite Thermal Imagery
A multi-temporal thermal atlas was created from 14 Landsat satellite images from summer scenes between 1990-2008 over the Greater Toronto area. The images were corrected and processed to estimate surface temperature. Given that each image would have slightly different climatic conditions, each image was normalized to establish a standard thermal regime. The normalized temperature maps were then compared to establish persistent hot/cool spots as well as thermal change over the study period.
Landsat 7 derived surface temperature map of the Greater Toronto area, June 29, 2007. The imagery shows that suburb developments in Mississauga and Brampton have the hottest daytime peak temperatures. Larger image
Although surface temperature is only a portion of the urban heat island effect, we still have a picture of the hot and cool neighbourhoods in the Greater Toronto area (above). Based on the imagery, during daytime peak temperatures, it is not the downtown core that is the hottest, but instead the new suburb developments of Mississauga and Brampton.
In-situ Network
Given that the surface temperature maps do not consider the atmosphere interaction (i.e. wind, humidity), nor the different rates of heat release during the night, it was important to obtain in-situ air and surface temperature measurements. A network of 30 temperature stations was installed over various urban and rural surfaces, collecting data from July 2007 to October 2008. Using the collected air temperature and surface temperature measurements as well as the satellite-derived surface temperature measurements, the urban heat island effect of the Greater Toronto area is being characterized.
Greater Toronto area in-situ measuring sites
Vegetation Cover Mapping
As is commonly considered, the presence of vegetation can cool a landscape, but to what extent is this applicable? Using high resolution Quickbird multispectral imagery, percent vegetation cover maps were produced and compared to the surface temperature maps. A per-pixel comparison between percent vegetation cover and surface temperature demonstrates a direct relationship between the two.
Percent vegetation cover map, surface temperature map and graphed per pixel comparison. This comparison indicates that the presence of vegetation can help cool landscapes
This activity is still in a production phase with expectations to have complete thermal mapping and UHI analysis results for the Greater Toronto area available for March 2009.
Links
Clean Air Partnership: www.cleanairpartnership.org