Effect of vegetation and waterbody on the garden city concept: An evaluation study using a newly developed city, Putrajaya, Malaysia Kenobi Isima Morris University of Nottingham Malaysia Campus, Malaysia abstract article info Article history: Received 16 September 2015 Received in revised form 25 March 2016 Accepted 25 March 2016 Available online xxxx The garden city concept was adopted in the development of a new tropical city, Putrajaya, aimed at mitigating the effect of urban thermal modification associated with urbanisation, such as urban heat island (UHI). WRF/Noah/ UCM coupled system was used to estimate the urban environment over the area and the individual thermal con- tributions of natural land use classes (vegetation and waterbody). A control experiment including all land use types describing the urban conditions of Putrajaya city agreed well with the observations in the region. A series of experiments was then conducted, in which vegetation and waterbody were successively replaced with an urban land use type, providing the basis for an assessment of their respective effect on urban thermal mitigation. Surface energy components, 2-m air temperature (T2m) and mixing ratio (Q2m), relative humidity (RH) and UHI intensity (UHII) showed variations for each land use class. Overall, an increase in urban surfaces caused a corre- sponding increase in the thermal conditions of the city. Conversely, waterbody and vegetation induced a daily re- duction of 0.14 and 0.39 °C of T2m, respectively. RH, UHI and T2m also showed variations with urban fractions. A thermal reduction effect of vegetation is visible during mornings and nights, while thatof water is minimally shown during daytime. However, during nights and mornings, canopy layer thermal conditions above waterbody remain relatively high, with a rather undesirable effect on the surrounding microclimate, because of its high heat capacity and thermal inertia. © 2016 Elsevier Ltd. All rights reserved. Keywords: Garden city concept WRF/Noah/UCM Urban heat island Putrajaya Waterbody and vegetation Tropical city 1. Introduction and background information At present, approximately 3.9 billion of the world population live in urban areas, which is expected to increase rapidly (United Nations, 2014). This could be due to the rapid rural-to-urban migration of people in developing countries (e.g. China, Brazil, India, Indonesia, Nigeria and Mexico). Urban areas occupy b 3% of the Earth surface (Liu et al., 2014) and the increase in the population of urban residents has exacerbated problems (e.g. waste management, increase in energy consumption, pollution and crowding) posed to the environment (Manning, 2011). Achievements in urban climate research have produced thermal posi- tive feedback of natural vegetation modification to urban engineered surfaces on the local and surrounding environment (Santamouris, 2014). This has caused government and private urban developers to adopt and adhere to mitigation guidelines in developing new and expanding existing urban cities. Urbanisation and relationship between the reduction in natural farmland and relative humidity (RH); increase of temperatures and significant urban heat island (UHI) effect; decrease of latent heat (LH) and increase of sensible heat (SH) fluxes; deterioration of visibility and urban heavy rainfall and local (regional) climate change are well established in the literature (Zhou et al., 2004; Hua, Ma, & Guo, 2008; Yao, Wang, & Wang, 2015). The impact of urbanisation is not only lim- ited to the city scale, but also on regional climate change. Much effort is made to estimate the contribution of current and future urbanisation to regional climate change. For example, Chen and Frauenfeld (2015) esti- mated that urbanisation will lead to an increase of temperature of ap- proximately 1.9 °C in the regional areas of China, because of altered land–atmosphere interaction. Wind flow; 2-m temperature (T2m) distribution and exchange of momentum, heat and moisture in urban cities are affected by surface modifications caused by developments and increased human popula- tion. In addition, urban surface energy balance is altered because of the conversion of greenery to artificial materials often characterised by low surface albedo and high heat capacity. These materials are used in the construction of roads, pavements such as the large expanse boulevard in Putrajaya, Malaysia (Moser, 2010), buildings and bridges. Most of these materials have low surface reflectance and albedo (Ahmed et al., 2015). In addition, the emissions from heavy-duty machinery, cars and other related equipment have only increased the environmental burden of city residents. In order to mitigate the problems associated with urbanisation and anthropogenic contribution of thermal fluxes to the environment, the garden city concept (GCC) proposed by Sir Ebenezer Howard (Howard, 1898), where cities are planned and built on undeveloped Computers, Environment and Urban Systems 58 (2016) 39–51 E-mail addresses: kenobimorris@gmail.com, kenobimorris@yahoo.com. http://dx.doi.org/10.1016/j.compenvurbsys.2016.03.005 0198-9715/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Computers, Environment and Urban Systems journal homepage: www.elsevier.com/locate/ceus