Urban heat island analysis of Greater Manchester, UK using sky view factor analysis

Abstract

The sky view factor has been used as an indicator of the amount of sky that can be seen from the ground in an urban area. It was also found to be correlated to the formation of urban heat island effect. Sky view factors can be calculated by analysing photographs taken with a camera with a fisheye lens. However, calculations of sky view factor can vary; therefore, a detailed and more accurate method was developed in this paper to analyse photos and to calculate sky view factors. This method can process the now available higher resolution black and white JPEG (the commonly used digital photo standard created by the Joint Photographic Experts Group) photos and can give more accurate sky view factor values than the previous methods. Sky view factor values were calculated for 59 sites where air temperatures were measured and logged in Manchester, UK. Urban heat island intensities were calculated and linear relationships between sky view factors and urban heat island intensities were found for both summer and winter. However, the linearity tended to be stronger with sites having sky view factor values smaller than 0.65, i.e. the deeper canyons. Practical application: The new method can be used to calculate sky view factors from photographs taken from a camera with a fisheye lens with the original JPGE format. Compared to the other two methods, this new method can deal with photographs with a higher resolution. The SVF values calculated can then be used with canyon models to estimate the maximum urban heat island effect of a particular building site. The SVFs were found to be useful indicators in Manchester, UK.