Surface cartography of urban heat islands (UHI) in urban areas, through the use of high resolution imagery.
ISBN 978-85-88783-11-9
Authors
1Baudouin, Y.
1UQAM Email: baudouin.yves@uqam.ca
Abstract
Urban heat islands (UHI) account for a substantial source of thermal degradation in our environment, thereby having a direct effect on the health of a population during periods of heat waves. We need only to recall the 75,000 deaths in Europe in 2003, 800 in Chicago in 1995 ... Naturally, the first to be affected by this, are the elderly, children and the underprivileged (both physically and socially). This phenomenon is not new; it came along with the advent of the industrial revolution and has taken on alarming proportions in many cities, both large and small. It is associated with highly mineralized areas and represents higher temperatures of at least 5 to 10° C within the immediate vicinity. Considering that over 50% of the global population now lives in urban areas and that this number is continually increasing, it is not surprising that the heads of various municipalities feel an urgent need to map these urban heat islands (UHI) on a recurrent basis, as well as to consult diachronic maps in order to better calculate their evolution, or to compare them with maps of vegetation (from the NDVI vegetation index) in order to better assess the impact and measures of mitigation of future development. As part of research projects conducted along with several government agencies (Center for Public Safety, Department of Public Health, City of Montreal, Environment Canada, UQAM and UdeM) we were able to produce several revised mapping products ranging from 1984 to 2011 using conventional satellite imagery (Landat 5, 7 and 8) and coarse resolution scaling (respectively 120, 60 and 100 meters). Although these maps are very useful in developing a regional portrait, they proved insufficient in meeting the evaluation needs of management practices (impact of green roofs? White roofs? Influence of the density of the construction area? Disposition and amount of green space? etc.). Thus, in 2012 the Departments of Geography at UQAM (University of Quebec in Montreal) and at UdeM (University of Montreal) conducted a pilot project on the use of TABI (Thermal Broadband Imager) airborne imagery and CASI (Compact Airborne Spectrographic Imager) by the Itres© company (Calgary, Canada) in very high resolution (25 and 80 cm). The idea for applying this technology came about after consulting the Pipa et al. article which makes use of the TASI (Thermal Airborne Spectrographic Image) imaging, with the objective to map certain urbanized areas south of Spain. These innovative images enable us to finely map the thermal behavior of urbanized areas at the building scale. This means a set of completely new mapping products which bring with them, among other challenges, the regular mapping obstacles we confront, especially in matters of classification and semiology. Therefore, from a regional map with an approximate scale of 1: 50000, we are now able to obtain a scale of 1:1000. This new mapping approach provides us with the opportunity to evaluate the thermal behavior of surface materials used and to propose newer and better adapted methods of mitigation to slow down the phenomenon of urban heat islands (UHI). To evaluate its accuracy, we have also compared these new maps to thermal images taken in the field and the results were positive. The cartographic methods used will also be presented.
Keywords
Urban heat islands; Health and thermal degradation; High resolution