Urban heat island characteristics in London during winter

This paper presents results characterising the urban heat island intensity (UHI) in London during the peak winter season. Most UHI studies focus on the phenomenon during the summer as this is the period when temperature peaks are observed. However, for urban planning mitigation strategies and building energy demand design, the heating season should be also considered, since proposed measures to alleviate the summer UHI might have a negative effect during the winter or intermediate seasons. The study carries out trend and regression analysis by controlling climatic and geographical variations in the data set following a methodology developed for studying summer UHI [Kolokotroni, M., Giridharan, R., 2008. Urban heat island intensity in London: an investigation of the impact of physical characteristics on changes in outdoor air temperature during summer. Solar Energy 82, 986–998]. It was found that average nocturnal UHI of winter periods are of similar magnitude to the summer periods but the peak winter UHI trends are not as regular as summer giving a first indication that the effect of climate and urban parameters is different. The regression analysis in this research uses six on-site variables namely aspect ratio, surface albedo, plan density ratio, green density ratio, fabric density ratio and thermal mass to carry out impact investigation in six data sets, categorised by three geographical location within London and three sky conditions and regional wind velocity. The above variables do not explain the changes in outdoor temperature as much as they did during summer period models. However, unlike summer, the winter climate control models have the same R2 indicating that most of changes in outdoor temperature are caused by climate factors and not the on-site variables.