Characterizing urban heat island in Montreal (Canada) Effect of urban morphology

The urban and built-up class is the most complex land category interacting with the atmosphere. In assessment of urban heat island intensity (UHII), urban canopy models (UCM) are coupled to mesoscale models to account for the momentum, heat, and turbulence kinetic energy of buildings. Since considering the actual structure of an urban area is not feasible, ideal urban geometries are proposed. Moreover, realistic estimation of mean height of buildings, deviation of building heights, frontal area density, and plan area density of a city is required for urban climate modeling. In this paper, we have selected four neighborhoods in Montreal (Canada) to compare UHII using a typical urban structure that has been proposed by earlier studies with UHII using the urban morphology of Montreal in current research. Simulations with Weather Research and Forecasting model coupled to a multi-layer urban canopy model and building energy model suggest that the UHII of Montreal can be underestimated by up to 1.2 degrees C (at 9 am) in July 14th, 2005, when urban morphology is not accurate. The energy consumption of buildings is also underestimated by a factor of three. The UCM has a detailed procedure that considers the multi-reflection between urban surfaces to estimate the energy budget of the canopy. Major portion of the absorbed energy in the canopy is from the solar radiation on urban surfaces, which is highly dependent on their sky view factors. We propose a new parameterization for sky view factor of walls and compare it with other parameterizations and approximated field data. Implementing the new parameterization decreases the predicted UHII and the energy consumption by 0.4 degrees C and 1% in the simulation period, respectively. (C) 2015 Elsevier Ltd. All rights reserved.