The effect of building height and façade area ratio on pedestrian wind comfort of London Leonidas Tsichritzis * , Marialena Nikolopoulou University of Kent, Centre for Architecture and Sustainable Environment, United Kingdom ARTICLE INFO Keywords: Urban morphology Building height Façade area ratio Wind speed ratio Wind comfort assessment Pedestrians London CFD ABSTRACT The evaluation of wind environment has been receiving increasing attention as it has been associated with issues related to the quality of the urban climate, such as heat island intensity and air pollution, affecting health and wellbeing in large metropolitan areas. Focusing on the context of London, this study aims to associate pedestrian level wind comfort with the characteristics of urban morphology that incorporate information about the height variability and the vertical dimensions of buildings. More than 20 case studies of different configurations and dimensions 500  500 m were examined through CFD simulations. For each case study, eight wind directions were tested and the BRE wind comfort criteria were implemented for the different outdoor human activities. The results reveal a strong connection between the ground level mean wind speed ratio and the development of acceptable or tolerable wind conditions for pedestrians. From the morphological indicators examined, façade area ratio was the most dominant on mean wind speed ratio and on the percentage of outdoor space which is comfortable for certain activities, especially for increasing values of plan area ratio. The results of the study indicate that façade area ratio should be taken into consideration for assessing pedestrian level wind environment. 1. Introduction Urban wind environment has been studied extensively since the 1970s consisting an important field of research, particularly for the populated urban areas. The continuously increasing need for new de- velopments in city centres where the available land is limited, such as London, has led in increasing building heights which change the char- acteristics of urban morphology and affect the local wind environment especially at the lower urban canopy layers. The present study is focusing on the effect of urban morphology on ground level wind conditions which may affect people's comfort or even safety. Pedestrian level winds are also important for improving air quality in cities, removing the pol- lutants at street level from vehicular traffic or industrial activity. In addition, they enhance natural ventilation and cooling by removing the heat from urban canyons either vertically or horizontally promoting the mitigation of the urban heat island effect which is a major concern for the centres of many metropolitan areas around the world. The magnitude of the effect of wind speed on the overall comfort or discomfort perception is related to the type of human activity as well as the duration of exposure. People who are sitting have different comfort requirements compared to those who are standing, walking, etc. Greater wind speeds may be acceptable for activities with short periods of exposure, such as walking fast, compared to activities which require longer periods of exposure such as sitting or waiting. However, as comfortable and safe wind conditions are unlikely to exist all the time, uncomfortable or even dangerous wind conditions may be acceptable but only for a certain percentage of time. Such considerations have been taken into account by architects, urban planners and local authorities in European temperate climates (Blocken and Carmeliet, 2004; Willemsen and Wisse, 2007), in cold climatic contexts with very high buildings such as in northern America (Stathopoulos, 2009) as well as in very dense highly populated cities of south-east Asia (Du et al., 2017) in order to provide safe and comfortable conditions for the pedestrians. Urban morphology influences significantly the wind characteristics at street level, which are little affected by the wind flow in the upper layers (Ricciardelli and Polimeno, 2006). Morphological characteristics related to height variations and vertical dimensions of buildings have been proved to influence pedestrian level winds. The majority of such studies have been carried out for generic building configurations and idealized building geometries. Different ways of expressing such morphological characteristics along with some key findings from previous studies are discussed below. * Corresponding author. E-mail address: L.Tsichritzis@kent.ac.uk (L. Tsichritzis). Contents lists available at ScienceDirect Journal of Wind Engineering & Industrial Aerodynamics journal homepage: www.elsevier.com/locate/jweia https://doi.org/10.1016/j.jweia.2019.05.021 Received 30 September 2018; Received in revised form 29 May 2019; Accepted 29 May 2019 0167-6105/© 2019 Elsevier Ltd. All rights reserved. Journal of Wind Engineering & Industrial Aerodynamics 191 (2019) 63–75