The ‘ecology in the city’ refers to the study of the natural ecological systems (fragments) within an urban ecosystem, i.e. different urban fragments as the analogues of their non‐urban counterparts, whereas ‘ecology of the city’ represents a much wider context where urban ecosystem itself is studied as an ecological system, i.e. the study of the interactions of various biological, built, and social components of the ecosystems within a city (Vasishth 2015; Pickett et al. 2016; Verma et al. 2020b). Based on these diverse concepts of the urban ecology, following sections shall provide a brief understanding of the urban ecosystems. In the next sections, climate change as an emerging challenge to the urban ecosystems has been discussed, followed by the possible urban ecological approaches for mitigating the ill effects of climate change in these highly heterogeneous and fragile ecosystems.
1.2 Components of Urban Ecology
An urban ecosystem is composed of several tangible and intangible components. Tangible components include the physical structures which can be natural (such as flora and fauna, water bodies, mountains, urban agriculture, etc.) or human‐made (such as built structures like buildings and building materials, roads, railways, health, and related infrastructural developments; energy sources like coal, liquified petroleum gas (LPG), wood; food supplies and waste generation, etc.). In addition, the intangible components include the ecosystems services derived from various natural systems, biogeochemical cycling, solar energy, and material flow in the urban areas (Verma et al. 2020a). These major components can be mainly divided into three sectors: (i) urban infrastructures associated with the urban heat island (UHI) effect; (ii) urban vegetation representing the green spaces and related ecosystem services; and (iii) urban metabolism which represents the flow of energy and materials within the urban ecosystems.
1.2.1 Urban (Built) Infrastructures
Urban infrastructures are built to provide the services and benefits to the urban inhabitants (Ma et al. 2020). Urban habitats are almost similar over large areas or human‐managed cities and microclimatic regions (Savard et al. 2000) having a central square with paved areas, residential areas, urban parks, urban agriculture, and some disturbed/unmanaged plots (Lososová et al. 2018). Considerable impervious surfaces such as roofs, roads, and paving are the most common features of urban infrastructure which sets cities apart from adjacent rural areas (Vasishth 2015). Both the components (viz. natural and artificial) of urban infrastructure help in the maintenance of the ecosystem functioning and health (Kattel et al. 2013). For example, vegetation cover and water bodies in the urban and peri‐urban areas provide habitats for biological diversity and help in maintaining the integrity of the natural/ecological and physical environments (Hofmann et al. 2012). In addition to the natural and artificial classification, urban infrastructures can also be classified into two major components viz. aboveground and belowground (Ma et al. 2020). Aboveground component comprises of the infrastructures at/on which citizens live in, walk on and ride on, such as buildings, parking lots, roads, sidewalks, green spaces, and public transportation (Andersson et al. 2014). Belowground component encompasses massive foundations of the buildings, subway lines, tunnels, gas lines, water and sewage pipes, stormwater management, electricity, and optical cables for providing various services to the citizens and ease in their livelihood (Sun and Cui 2018; Ma et al. 2020). Both the components of the urban infrastructures hold crucial significance and interact with each other in complex ways (Pandit et al. 2015). Aboveground infrastructures provide living spaces and comforts to the citizens, whereas belowground components play equally important services in the form of utilities, transportation, biomass, and structures which enable the urban areas for smooth functioning of the aboveground components (Ferrer et al. 2018; Ma et al. 2020). Moreover, natural components of the urban infrastructures such as plant roots and microbial communities also show strong competition for the space in the belowground components (Mullaney et al. 2015).
Land‐use and land‐cover changes are one of the major drivers of global change processes which should be taken into account considerably from ecological point of view (Vitousek 1994). Urban land cover has been projected to increase by 200% within the first three decades (2000–2030) of the twenty‐first century (Elmqvist et al. 2013). These projections revealed that there has been and would be a massive investment in the development of the urban infrastructures at the cost of consumption of natural ecosystems/landscapes (Green et al. 2016). Increase in impervious surfaces and the materials used for their formation (dark asphalt and roofing materials) due to massive urbanisation have the ability to absorb the solar irradiance and influence the local climate and hydrological conditions (Vasishth 2015). UHI effect (described later) is one of the major outcomes of the increase in such urban built infrastructures (Jaganmohan et al. 2016). For managing the urban ecological components (e.g. biodiversity, nutrient cycling, etc.) influenced by the land‐use change patterns, several conceptual frameworks, and models have been developed (Pickett et al. 2011). However, their proper implementation is lacking due to poor representation of the social components in these frameworks (Zipperer et al. 2011). Nowadays landscape urbanism is the emerging concept with non‐hierarchical, flexible and strategic planning where landscapes in the urban areas are designed and managed as per the demand of the society (Kattel et al. 2013). Detailed elaboration of such strategies and frameworks has been given in the later sections of the chapter.
1.2.1.1 Urban Heat Islands
Modifications of the physical environment by the built structures during the process of urbanisation impede the energy distribution and composition of gases in the near‐surface. It alters the microclimatic conditions by modifying the thermodynamics of the urban ecosystems which resulted in 2–5 °C higher ambient temperature than the surroundings (countryside/rural) areas (Phelan et al. 2015; Jaganmohan et al. 2016; Vasishth 2015; Duffy and Chown 2016). Such alterations in local and regional climatic conditions (temperature dynamics) by the urban infrastructures lead to the UHI effect (Dallimer et al. 2016; Zhou et al. 2017; Hu et al. 2019). The UHI effect is one of the most prominent human‐made climatic phenomena in the urban ecosystems and has considerable ecological significance (Gaston et al. 2010; Akbari and Kolokotsa 2016; Yu et al. 2017). The UHI effect leads to the alteration of local and regional climatic conditions, impedes with the wind flows, and turbulence, related with shifts in cloud formation and precipitation, air pollution, and higher greenhouse gas (GHGs) emission (Seto and Shepherd 2009; Gaston et al. 2010). The increase in air pollution, heat stress, water quality, food security, and disparity in ecosystems services due to the UHI effects further affect the health and comfort of the urban inhabitants, thus, have adverse social, economic, and ecological impacts (Chang et al. 2016; Wong et al. 2016; Battles and Kolbe 2019). Moreover, UHI effect is further expected to contribute in the global climate change by increasing the GHGs (particularly CO2) emission from the urban areas (Rosenzweig et al. 2010), and in response, the UHI effect's impact may further intensify in most of the cities (Chapman et al. 2017). However, the magnitude of the UHI effect depends on several local and regional factors such the latitude, weather and climatic conditions, diurnal conditions, rainfall, surrounding ecology, population and culture of the city, and the urban planning (Zhao et al. 2014; Vasishth 2015). For example, the increase in temperatures due to UHI effects during winter at higher altitudes, and during summer at lower altitudes may decrease and increase the costs of air‐conditioning, respectively (Vasishth 2015). Thus, the UHI effects may have variable responses depending on the location of the urban area and it needs to be explored further under the changing environmental conditions.
1.2.2 Urban Vegetation
Urbanisation provides a unique habitat for vegetation growth. Urban vegetation (tree, shrub, or ornamental plants) is comprised of both native and exotic species (Cubino et al. 2021). Two major processes are involved in the growth of urban vegetation, viz. cultivated vegetation growth which represents the plants that are introduced and managed by the urban inhabitants, and spontaneous vegetation growth which have been established and colonised without the human‐assistance (Cubino et al. 2021). Vegetation composition of the urban areas even differs at small scales depending on the several social factors (Čeplová et al. 2017). Introduction
