and landscape planners to interact and develop management systems for tackling different environmental issues (Pauleit et al. 2011). Green infrastructures can help in alleviating the impacts of UHI effect; however, UHI effect alternatively impacts the vegetation phenology, therefore, the role of these infrastructures in reducing UHI effect needs further research (Niemelä 2014; Dallimer et al. 2016). Therefore, increasing interests have been reported in investment in green infrastructure development and urban ecosystem regeneration in the recent years (Green et al. 2016). By having multiple benefits, green infrastructures are considered to play a major role in climate change adaptation (Ramyar and Zarghami 2017). Detailed viewpoint on different types of green infrastructures and their role in combating climate change has been given in the following sub‐sections.
1.5.3.1 Green Space Development
Urban greening programmes are the leading features of the policies related to the climate change mitigation (Weissert et al. 2014). In view of ongoing climate change, potential research and management emphasis has been given to identifying the impacts of socio‐demographic and environmental drivers on green spaces and the benefits derived from their conservation (Niemelä 2014; Verma et al. 2020c). The key tangible ecosystem services derived from the green spaces include mitigation of air pollution and UHI effect as well as physical and physiological health benefits to the residents (Verma et al. 2020b; Wang et al. 2020). Cooling effect provided by the green spaces is the most important ecosystem service which helps in mitigating UHI effect (Yu et al. 2017). The cooling effect of green spaces has been extensively explored by several researchers which involve two eco‐physiological mechanisms viz. evapotranspiration and shadowing (Jiao et al. 2017; Wang et al. 2020). Size and characteristics (shape, structure, and composition/configuration) of green space is more important for cooling effect as it increases with increasing size of the green spaces (Jaganmohan et al. 2016; Yu et al. 2017); however, it is still controversial and several other factors come into the play (Monteiro et al. 2016). However, there is a threshold value of efficiency (TVoE) above which increase in vegetation cover may not lead to a consequent decrease in land surface temperature (Bao et al. 2016; Yu et al. 2017). Tree‐based green spaces showed the highest cooling effect followed by bush and grassland (Kong et al. 2014). Since the canopy size and structure vary with the tree species, they provide different wind speed patterns which resulted in variable cooling effects (Armson et al. 2012). In addition, different trees have different eco‐physiological mechanisms (e.g. evapotranspiration and leaf area index) which depend on the resource availability and management practices (Wang et al. 2020). Kuang et al. (2015) observed a positive correlation between the cooling effect of green space and normalised difference vegetation index (NDVI). In addition, the presence of water bodies along with the green spaces improve the cooling effect. For example, green spaces connected with water bodies showed higher cooling effect, whereas grassland‐based green spaces showed weak cooling effect (Yang et al. 2020). Therefore, for climate change mitigation, interconnected green space and water body conservation and development are strongly suggested (Yu et al. 2017).
The magnitude of reduction of the temperature by one unit with the increase in vegetation (tree) cover is known as cooling efficiency (CE) which varies with the size and shape of the green spaces (Zhou et al. 2017; Wang et al. 2020). Compact green spaces with circular or square shapes provide more CE (Yu et al. 2017). Moreover, the regional climatic conditions also play a major role in shaping the vegetation structure and composition, thus, affecting CE (Richards et al. 2019). An extensive study was conducted by Wang et al. (2020) for 118 cities from 10 different biomes for observing the variation in CE. They used ordinary least squares (OLS) linear regression models with the percent of tree (Ptree) as independent variable and land surface temperature as dependent variable. They found the variation in CE from 0.04 to 0.57 °C with an average value of 0.17 °C where Ptree explained the 40.3% of the variation in the land surface temperature. Moreover, they observed that the biomes dominated by broadleaved trees reflect higher CE as compared to the biomes dominated by coniferous or sparse trees (e.g. savannas and shrublands). In addition to the inter‐city variations, intra‐city variations in CE were also observed, depending on the social and ecological contexts (Myint et al. 2015). Moreover, cities with hot and dry conditions (Mediterranean and desert biomes, e.g. Phoenix and Las Vegas) showed higher CE (Myint et al. 2015), whereas cities with hot and humid conditions (e.g. Nanjing, Beijing, Shenzhen, and Baltimore) reflected lower CE (Zhou et al. 2017). Exploring such scenarios for different cities from the developing and/or tropical nations could further help in mitigating UHI effects and adaptation to the climate change (Wang et al. 2020).
In addition to the direct reduction in land surface temperature, urban vegetation/tree shading also reduces the CO2 emissions from the buildings by cutting air‐conditioning costs during different weather conditions (Asgarian et al. 2015; Niemelä 2014). Moreover, visiting green space provides several benefits to the human in terms of health and well‐being; however, there is no conclusive research on the mechanism underlying such results (Wu 2013). Therefore, there is a need for interdisciplinary researchers including the sociologists, psychologists, public health practitioners, anthropologists, and the ecologists to explore the mechanisms behind the linkages between human health and green spaces (Tzoulas and Greening 2011). Further, planning and management of green spaces of an area have been influenced by several factors including from the personal/resident/owner level to the government and political levels which determine the type and size of vegetation (Niemelä 2014). Urban green spaces in cities are needed to plan in such a way that they can contribute to the climate change mitigation, by integrating and planting trees having optimal evapotranspiration potential and physical shading (Niemelä 2014; Vasishth 2015).
1.5.3.2 Green‐roofs
To mitigate the UHI effect, several measures have been applied and adapted in the urban areas. The examples include the use of heat‐reflecting surfaces and materials like sunward‐oriented roofs, roads and pavings, use of light‐coloured materials, increase in the proportions of vegetation to the hard landscapes, etc. (Vasishth 2015). In addition to these measures, adoption of roof‐top gardens or green‐roofs is the emerging field of research for reducing the UHI effect and mitigating the climatic change (Niemelä 2014). As like the functions of green spaces, green roofs also help in cooling by evapotranspiration mechanism. Earlier, green roofs were thought as the burden to the buildings, but now they have been gaining wider attention by the researchers as well as the urban residents as the additional protective covering to the roofs for protection from the heat stress (Vasishth 2015). Studies revealed that well‐designed and constructed green roofs may help in increasing the life of roofs and waterproofing structures even during the hot summer days (Vasishth 2015). However, research on exploring the ecosystem services to the humans (social and aesthetic benefits) provided by the green‐roofs still needs attention of the scientific communities (Jungels et al. 2013; Niemelä 2014).
1.5.3.3 Green Building
The built infrastructures utilise massive amount of resources and energy and produce substantial amount of waste products and GHGs emission as the output (Singh and Raghubanshi 2020). In this view, the U.S. Green Building Council's (USGBC) Leadership in Energy and Environmental Design (LEED) has launched a certification programme in 2000 with the aim ‘to develop and encourage green building expertise across the entire building industry’ (www.usgbc.org). The LEED programme is one of the key certification programmes for developing site‐specific building strategies and promoting the native plant diversity and water body conservation (Steiner 2014). This programme has four levels of certification, viz. certified, silver, gold, and platinum, depending on the credits received by a building project for six different categories which are: sustainable sites, water efficiency, indoor air quality, energy and atmosphere, innovation and the design process, and material and resources (Steiner 2014). Thus, the green buildings are the new initiatives launched by different agencies for the sustainable urban development and climate change adaptations. A few green building programmes viz. LEED India and the Green Rating for Integrated Habitat Assessment (GRIHA) in India are the two major certification
