by Jasper Wong
The Humber River Catchment (HRC) is an essential area within Lake Ontario’s basin. Covering 900 km^2, it houses over 850,000 residents and stands as the largest area overseen by the Toronto and Region Conservation Authority (TRCA). As urban development and population growth influence the HRC, its land dynamics and biophysical attributes transform, raising questions about ecological balance and human comfort.
Under the guidance of Professor Adeyemi Olusola for my EUC Undergraduate Research Award (EUCURA) project, I studied the HRC's land use changes from 1990 to 2022 by using Google Earth Engine. This research particularly targeted urban transformations in the Humber River Basin of the Great Toronto Area.
My initial task in the project was to become proficient in using Google Earth Engine and then to develop Supervised Classification maps of the HRC. By applying Landsat 5 imagery from 1990 and Sentinel 2 from 2022, I identified urban areas and differentiated them from natural spaces (forest, grassland, and water). Indices like NDVI, MNDWI, NDBI, and BSI were employed in this process, with Ground Control Points helping to refine the classifications.
After classifying the land covers, I focused on the Land Surface Temperature (LST) and Emissivity within the HRC for both years. Data from Landsat 5 for 1990 and Landsat 8 for 2022 were used for this part.
The results from the classification maps were clear: urbanization had increased from 1990 to 2022. This was evident as more buildings, roads, and urban infrastructure marking its terrain in 2022 compared to 1990, shown as red pixels, appeared in the 2022 imagery, especially towards the center and north of the HRC. (Figure 1 and 2) Typically, one might assume that as areas become more urbanized, they would also become warmer due to factors such as heat-absorbing concrete surfaces (low albedo), reduced vegetation, and increased human activity, which known as urban heat island effect.
However, our findings in the HRC challenge this notion. Despite the obvious increase in urbanization, there wasn't a significant rise in temperatures by 2022. (Figure 3, 4, 5, and 6) This indicates that there might be other mitigating factors impacting the temperature, keeping it from rising drastically.
These findings highlight the growth of urban areas in the HRC. However, the cooler temperatures in 2022 compared to 1990 challenge common beliefs about urban heat effects. This research has provided insights into the relationship between land use changes and temperatures, suggesting that urban growth in the HRC might not necessarily lead to warmer temperatures. Therefore, in the next phase of this research, we will find out the reasons behind these temperature dynamics.
Jasper Wong is a recipient of the EUC Undergraduate Research Award (EUCURA) and worked on the project on Land use/Land cover dynamics and land surface temperature within the Humber River Catchment using Remote Sensing and GIS with Professor Adeyemi Olusola.