Climate change has severe impacts on cities in many countries. This review covered climate change sources, consequences, and options for mitigation and adaptation in cities. The global rate of urbanization rose from 13% in 1900 to 52% in 2011. However, the links between urbanization and greenhouse gas emissions remain complicated, influenced by factors such as demographic structure, economic growth, individual income and lifestyles, the nature of urban systems, urban form, and geographical location. These drivers cause climate-induced vulnerabilities in cities, such as drinking water shortages, health impacts, and severe extreme events. Population, urban form, and infrastructure might increase these vulnerabilities. In cities, efficient energy consumption, multi-modal transportation, hydroelectrically powered transportation, land use planning, building direction, height-spacing densification of structures, multiple centers, mass transportation, and non-motorized transportation are found as the main mitigation measures. Likewise, adaptation measures include space greening, green infrastructure, ventilation and air-conditioning, blue spaces, flood protection embankments, polders, dams, etc. Spatial planning is crucial for executing local, regional, and international mitigation and adaptation policies and agreements. To make cities and communities less vulnerable to climate change, these policies and agreements might include: how land is used and developed; how non-fossil fuel energy is promoted; and how buildings and transportation systems use less energy.
Department of Land Record and Transformation, Patuakhali Science and Technology University, Bangladesh
Human activities in the natural environment play a significant role in global warming and contribute to the increasing emission of greenhouse gases in the atmosphere. Fossil fuels induced greenhouse gas emissions occurred on a large scale during the In-dustrialization period, which led to urbanization. Further, urbanization contributes to land transfor-mation with-in and near the urban area. It is reported that many cities in Asia are found as the epicenters of economic growth and a major source of green-house gas emissions (Gu & Han, 2010; IPCC, 2007; Umezawa et al., 2020). Globally, about 55% of the worlds population lives in cities in 2018, while it was only 30% in 1950. This urban population is projected to increase by 68% by 2050. In 2018, Africa (13%) and Asia (53.7%) were home to almost two-thirds of the global urban population. It is esti-mated that together, they will be home to three-fourths of the urban population by 2050 (United Nations, 2019).
The key determinants of global greenhouse gas emi-ssions and climate change are population growth, patterns of economic activity, energy demand, build-ing design and infrastructure, lifestyle, land-use pat-tern, geographical location, and current climate poli-cies, all of which are linked to the urbanization pro-cess (Abubakar & Dano, 2019; Dodman, 2011; Minx et al., 2011; Siddik et al., 2021; Siddik & Zaman, 2021; World Bank, 2010). Human behaviors have a significant impact on the climate in urban areas as their emission effects vary significantly from those in neighboring rural areas (Salleh et al., 2013).
The Intergovernmental Panel on Climate Change (IPCC) distinguishes energy supply (26%), trans-portation (13%), residential and commercial build-ings (8%), industry (19%), agriculture (14%), land use change and forestry (17%), and waste and waste-water (3%) as the key contributors to worldwide greenhouse gas (carbon dioxide, nitrous oxide, meth-ane, and ozone) emissions (Barker et al., 2007). However, greenhouse gases are generated by a variety of activities in cities, including power gene-ration, infrastructure, services and manufacturing industries, and transportation (Dodman, 2011). The energy consumption rate of urban areas is found to be twice as much as rural areas, but they are respon-sible for almost three-quarters of global CO2 emi-ssions (Shahjalal, 2021; Hoornweg et al., 2011).
Climate change poses a major threat to the urban environment and its economy worldwide. Its conse-quences are likely to worsen shortly. Many urban areas are prone to being impacted by extreme wea-ther events such as higher annual rainfall, tropical storms, lightning, and flooding, as well as heat island effects (Grafakos et al., 2018, 2020; Shalaby & Aboelnaga, 2018). In cities, the human population, water resources, biodiversity, buildings, and infras-tructures are extremely susceptible to the conse-quences of climate change, including sea-level rise, urban heat island, tidal surges, floods, and droughts. Moreover, climate change has an effect on how stakeholders in the city behave. These behavioral changes are expressed in a variety of ways in the urban system, including morphological changes in the city, institutional, operational, economic, cul-tural, social, and environmental changes (Attaur-Rahman et al., 2016; Balaban & Puppim de Oliveira, 2014; Grafakos et al., 2018, 2020; Shalaby & Aboe-lnaga, 2018).
Grafakos et al. (2018) describe the development and implementation of policies and actions to reduce cur-rent and future anthropogenic greenhouse gas emiss-ions, known as mitigation strategies, as well as res-ponses to climate change-induced impacts and unce-rtainties for adjusting the built environment to miti-gate the adverse effects of extreme events, known as adaptation measures. Cities are taking the lead in climate change mitigation and adaptation by reduc-ing greenhouse gas emissions, building resilience, and promoting sustainability (Pietrapertosa et al., 2018; Solecki et al., 2015). This role has been reflec-ted by signing up to different agreements in inter-national charters and meetings, including the United Nations Framework Convention on Climate Change (UNFCCC) signed in 1992-93 but effective from 1994, the Kyoto Protocol signed in 1997 but effe-ctive from 2005, and the Paris Agreement signed and effective from 2016 (Kuyper et al., 2018). This re-view looked at how climate change affects cities and what they can do to mitigate or adapt to it.
Researchers used academic databases and search engines such as ScienceDirect, Web of Science, Sco-pus, Google Scholar, PubMed, and Science Open to conduct literature searches on the subject matter. Various keyword combinations such as cities and climate change, urban and climate change, climate change effects on cities, urban drivers of climate change, climate change mitigation, climate change adaptation, urban forms, green spaces and climate change, blue spaces and climate change, urban green transportation, and policies for climate change miti-gation adaptation were used until the middle of 2022. Duplicate literature was removed after screen-ing the results of the literature search. Relevant liter-ature was identified at this stage. The findings of this review are presented in Section as urban drivers of climate change, effects of climate change on cities, and climate change mitigation-adaptation). Finally, some concluding remarks are made in the conclusion section.
Urban Drivers of Climate Change
Urban areas, in the context of climate change, signi-ficantly differs from rural areas in many countries. The global rate of urbanization has risen from 13% in 1900 to 36% in 1970 and 52% in 2011, but the links between urbanization & GHG-emissions levels remain complicated and require various drivers such as population and demographic structure; economic growth; individual income and lifestyles; the nature of urban systems; urban form and design; and geo-graphical location (Blanco et al., 2015; Dodman, 2011; Minx et al., 2011; Shalaby & Aboelnaga, 2018). With the rapid growth of urbanization and industrialization in Asia, anthropogenic emissions have accelerated more than in many other Western countries in recent decades (Patella et al., 2018).
Population and demographic structure
The global population grew by almost 87% between 1970 and 2010, to about 6.9 billion in 2010, from 3.7 billion in 1970 (Blanco et al., 2015; United Nations, 1999). About 55% of the global population lived in cities in 2018, and that is expected to rise to 68% by 2050. According to this project, about 2.5 billion more people will be added to cities because of rapid urbanization (United Nations, 2018). Each additional person raises GHG emissions, while the contribution rate varies greatly depending on their socioeconomic and geographic circumstances (Dietz & Rosa, 1997; ONeill et al., 2012). The global urban population has increased dramatically from 0.75 billion (1950) to 4.2 billion (2018). Despite its lower degree of urbanization, about 54% of the global city popu-lation exists in Asia (United Nations, 2018). For exa-mple, the 35 largest and most important cities in China account for 18% of the countrys population, and these cities are accountable for about 40% of the energy-related CO2 emissions (Dhakal, 2010).
Economic growth
Across countries, per capita energy consumption is closely associated with per capita income (Kraus-mann et al., 2008). Its possible that economic grow-th in developing countries would be more emissions-oriented than in developed economies (Jakob et al., 2012). Rapid economic growth in middle-income countries continues to devastate the effects of carbon emissions, resulting in strongly increasing emissions. However, since economic growth in developed coun-tries is slower, the impact of technological change is more noticeable, and emissions rise quite slowly or decrease (Brock & Taylor, 2010). Hence, it is evi-dent that energy consumption and its environmental impacts go up or down quite slowly in the early stages of economic cycles and afterwards decrease more rapidly throughout the later stages (Grossman & Krueger, 1994; Jotzo et al., 2012). From 1970 to 2010, Asia had the worlds fastest economic growth, averaging 5.0% per year. In all regions except Asia, per capita emissions have decreased over time. Des-pite this convergence, there are still significant diff-erences in per capita emissions between countries (Matisoff, 2008; Pellegrini & Gerlagh, 2006; Stern, 2012). Consumption-based greenhouse gas emissi-ons are highly associated with the economic growth of a country. It may be a developing or developed country. Researchers found that rising consumption is the main cause of rising emissions in the Nether-lands between 1987 and 1998 (De Haan, 2001) and in the UK between 1992 and 2004 (Baiocchi & Minx, 2010). Within cities, the types of economic activities that have an effect on green-house gas emissions. Capitalist manufacturing and industries that use a lot of energy are strongly linked to more pollution, especially when the energy they use comes from fossil fuels (Dodman, 2011).
Individual income and lifestyles
We follow a consumption lifestyle as we consume more and use more resources in our real experiences, resulting in increased emissions from our lifestyles. Between 1992 and 2007, urban development and lifestyle changes in China contributed to an increase in energy-related carbon dioxide emissions (Minx et al., 2011). The lifestyle we lead largely depends on the household income. The amount of household income is noteworthy as it influences house size as well as the housing neighborhoods thermal comfort threshold temperatures (Blanco et al., 2015; Ken-nedy et al., 2009). However, a high quality of life can be found in cities without releasing significant quantities of greenhouse gases. There are so many cities across the worlds that have low energy con-sumption while still ensuring a comfortable lifestyle (Spivak, 2011).
Nature of urban system
Urban systems lead to climate change because of their several functions, including spatial, transport, and supply functions, which require huge amounts of fossil fuels. Spatial urban functions include buildings to house people and industry, and spaces for social-cultural and economic interactions (Shalaby & Abo-elnaga, 2018). Buildings accounted for 28% of worldwide energy-associated CO2 emissions, with direct CO2 emissions from the burning of fossil fuels responsible for nearly a third of the total emissions. In addition to that, another 11% of CO2 emissions from the energy sector originated from the cons-truction process, including the process of building raw materials including cement, steel, brick, etc., transportation of raw materials, and the construction process (UN Environment and International Energy Agency, 2017). Urban transportation functions inc-lude the movement of people, raw materials, and products towards and from urban areas as well as their periphery (Shalaby & Aboelnaga, 2018). In 2010, final energy demand for transportation acco-untted for 28% of total end-use energy, with about 40% of that used in urban transportation (Sims et al., 2014).
Urban form and design
Urban form and design can have an inclusive range of consequences for an urban areas greenhouse gas emissions. Denser buildings require less energy to heat. In addition to that, single-family housing uses more energy to heat and cool than the other types of dwellings. Furthermore, a multi-functional neighbor-hood is more practical than a mono-functional neigh-borhood for decreasing energy demand and consum-ption ratio and for encouraging walking, cycling, and other non-motorized vehicle travel (Dodman, 2011; Farjam & Hossieni Motlaq, 2019; Keeley & Frost, 2014). Hence, its likely that urban design will exa-cerbate climate change effects and make urban spa-ces more vulnerable. Bitumen, pavement, and other hard surfaces absorb solar heat, resulting in a heat island in urban areas that contributes to rising urban temperatures (Shalaby & Aboelnaga, 2018).
Geographical location
A citys GHG emissions are highly influenced by its geographic position. The amount of energy needed to heat urban buildings is now heavily influenced by the climate of the area, especially on warm days (Kennedy et al., 2009). It is evident that household energy use (such as heating, cooling, and lighting) or household GHG emissions in an urban area obvi-ously depend on its geographical location (Dodman, 2011; Kennedy et al., 2009). In the United States, cities with colder winters have higher home heating emissions in January, whereas cities with hotter sum-mers have higher energy use linked with home cool-ing in July (Glaeser & Kahn, 2010). On the other hand, hydropower access for generating electricity in cities like Geneva in Switzerland, Toronto in Cana-da, Rio de Janeiro in Brazil, etc. considerably dimi-nishes the concentration of greenhouse gas emissions (Kennedy et al., 2009; Schmidt Dubeux & Rovere, 2007).
Effects of Climate Change on Cities
Climate-induced vulnerabilities in the cities may inc-lude unavailable drinking water, health impacts, sev-ere and intensive extreme events, e.g., floods, cyc-lones, storm surges, heat waves, etc. These vulner-abilities can be extended or triggered based on the agglomeration of people, urban activities, and infra-structure in the cities (Condon et al., 2009; Shalaby & Aboelnaga, 2018).
Effects of extreme weather events
Cities are incredibly susceptible to natural disasters, which are predicted to occur more frequently as a result of climate change. Cities are becoming denser and, in some cases, larger or both because of upward urban population growth. This upward trend makes cities more vulnerable to all kinds of extreme events (Masson et al., 2020). A total of 530 cities, compri-sing 517 million people around the world, were reported as vulnerable to climatic hazards in 2018 (CDP, n.d.). By 2050, people will be twice as likely to be affected by extreme weather events like floods, cyclones, and tidal surges as they are now (World Economic Forum, 2014). In Asia, nearly all cities are susceptible to multiple natural hazards, including flooding, cyclones, storm surges, heat waves, seale-vel rise, excessive rainfall, droughts, etc. (Shaw et al., 2009; Shaw & Sharma, 2011). Super Typhoon Hai-yan and its associated storm surge cost USD 13 bil-lion in Chinas coastal cities (Caulderwood, 2014). In 2005, the Mumbai flood cost USD 100 million. In Hanoi, about 20 thousand households were affected and 45 thousand ha of secondary crops were dam-aged in the 2008 flood. The total estimated loss was USD 1.6 million (Mulyasari et al., 2011). Church and White estimated global mean sea-level (GMSL) rise using satellite altimeter records and in-situ reco-nstruction and found 3.2 ±4 mm year-1 rise in GMSL from 1993 to 2009 (Church & White, 2011). Climate change effects on sea-level rise can be felt both directly and indirectly. Changes to the coast-line, coastal flooding, coastal erosion, disruption and damage to natural ecosystems and coastal infrastru-cture, displacement, saltwater intrusion (into estu-aries, surface water, and ground water), high storm surges during cyclones, rising ground water tables near to the coast, etc., are all examples of direct effects. In addition, possible indirect effects include changes in soil properties, ecosystem functions, coastal dweller economic activities, psychological effects, recreational effects, land use change, and so on (Dwarakish et al., 2009; Hunt & Watkiss, 2011; Lankao & Gnatz, 2008; Siddik et al., 2018). Many large cities are situated in low-lying areas or along the coast with huge human populations (65% of coastal cities have more than 5 million people) and are the hub of national economic activities, including trade and commerce, and are highly vulnerable to sea-level rise and its associated inundation, high storm surge, erosion, etc. (McGranahan et al., 2007; Nicholls, 2004). Floods have struck three to nine times more frequently than they did five decades ago in eight coastal states in the United States and cost US $14.1 billion between 2005 and 2017. Coastal flooding days have increased significantly in 27 states from a yearly average of 2.1 days during 1956-1960 to 11.8 days during 2006 - 2010 (Amadeo, 2020). In Asia, the majority of large cities are clust-ered along the coastal areas of the Indian and Western Pacific Oceans. These cities are significant-ly affected by sea-level rise and associated impacts (Shaw & Sharma, 2011). In the last century, the Indian Coast has experienced a mean sea-level rise of mostly less than 1 mm (Unnikrishnan et al., 2006). About 1% of Indian coastal cities will be inundated or more than 1% of the urban population will be affected by a 3m sea-level rise (Revi, 2008).
Effect on temperatures
Climate change is expected to reduce heating dem-and during the winter while increasing cooling dem-and in the summer. However, the magnitude of such effects is significantly influenced by their geographi-cal location (IPCC, 2001). The likelihood of a link between climate change and an increase in the severity of heat waves is very high. Rising temp-eratures can result in discomfort, monetary disrupt-tion, displacement, and higher death rates. Heatwa-ves reportedly cause an increase in fatalities and casualties in Europe and North America. However, they are also associated with age, location, and socio-economic conditions (IPCC, 2014). Another example: the industrial development and economic prosperity of Brazil are significantly dependent on hydropower, which is extremely susceptible to chan-ging patterns of precipitation (Geller et al., 2004). Heat waves hit much of Europe in the summer of 2003. Seasonal temperatures in Portugal, France, Italy, England, and Wales are found to be the hottest years on record, which causes an enormous mortality rate (Conti et al., 2005; Johnson et al., 2005). In all Italian capitals, mortality increased by 3134 in 2003 during the three summer months compared to the previous year (Conti et al., 2005). Furthermore, a total of 2139 additional deaths occurred in England and Wales in August 2003 (Johnson et al., 2005). Moreover, heat stroke claimed a total of 3,442 peoples lives in the United States during 1999 – 2003 (CDC, 2006). The IPCC forecasts that heat waves will become more intense and occur at a higher frequency in the years to come. This will make people temporarily uncomfortable and give them respiratory illnesses. It will also make cities need more energy to cool down (Ampatzidis & Kershaw, 2020).
Effect on water resources
Urban water resources comprise underground water, surface water (inland), seawater, and rainwater. Cli-mate change, urban heat islands, flooding, cyclones, storm surges, droughts, and sea-level rise all have potential consequences for urban wetlands (Diaz & Yeh, 2014; Jamei & Tapper, 2018). The effects are a reduction in the availability of water, both surface and ground water; increased water demand; hamper-ed water supply systems, including infrastructure and treatment; deteriorating water quality, etc. (Hunt & Watkiss, 2011; UN-Habitat, 2011). Climate change has hastened urbanization along with popu-lation growth and intensified water usage, putting more pressure on urban water sources (WHO, 2017). In addition, increases in mean air temperature would accelerate evaporation and increase water demand for cooling in buildings, potentially driving up total per capita water consumption (Ali, 2009; Diaz & Yeh, 2014; Hunt & Watkiss, 2011). An increasing population and mean air temperature would necessi-tate a significant increase in urban water demand (Lv et al., 2020). Drought and prolonged periods without precipitation would inevitably result in a reduction in the supply of potable surface water and groundwater recharge (Diaz & Yeh, 2014). Such negative effects significantly decrease the availability of freshwater in semi-arid and arid regions. Kundzewicz et al. (2007) stated that water supplies are likely to drop in the Western United States, the Mediterranean Basin, northeastern Brazil, and southern Africa. Sea-level rise may cause salt water to seep into surface and ground water in coastal cities (Diaz & Yeh, 2014; Lv et al., 2020). Reduced river flow is considered a key cause of the development of severe saline conditions at the estuary, as saline seawater eventually flows upstream. Seawater can also make coastal ground-water salty by seeping in from the side or from below (Diaz & Yeh, 2014).
Effects on human health
Extreme heat is one of the most hazardous environ-mental conditions, impacting people (heat-related death and illness) in many countries (Kalkstein et al., 2009). Human tolls and causalities are the direct effects of several natural calamities frequently cau-sed by climate change (Hunt & Watkiss, 2011). A total of 2039 human tolls due to heat stroke were recorded in the United States between 1999 and 2010. While this situation worsens over time among all climate change-related fatalities (Leighton, 2019), an average of 1500 deaths are recorded during the summer (Kalkstein et al., 2009). An extreme heat-wave killed over 70,000 people in Europe in 2003 (Leighton, 2019). More than 1,000 people died in Mumbai in 2005 because of a tropical cyclone and the 94 cm of rain that fell in 24 hours (de Sherbinin et al., 2007). Besides, psychological effects include-ing post-traumatic depressive illness, anxiety, com-plicated grieving, and sadness are also observed foll-owing disaster events (Silove et al., 2006). Further-more, changing seasonal climate conditions, such as temperature, precipitation, and humidity, can alter the distribution pattern of disease vectors, potentially increasing health illnesses such as diarrhea, fever, and so on (Costello et al., 2009). The expanded dis-tribution zone of disease vectors will result in an additional 260 – 320 million individuals being infec-ted by malaria worldwide by 2080 (Lindsay & Mar-tens, 1998). Furthermore, acute famine is often an outcome of extreme weather conditions, which can have a substantial bearing on the health of people. Severe famine incidents have been recorded in the past as a result of climatic variations. The great mediaeval famine of Europe (1315 - 1317) is a case of climate-induced severe crop shortages, food price increases, starvation, and death (Mcmichael, 2003). Climate change and the rapid acceleration of its app-earance in the past few decades, together with hunger, disparity, and contagious and non-communi-cable diseases, pose a significant threat to public health. Climate changes health effects will impact most communities, both rural and urban, in the upcoming decades, putting billions of peoples lives and well-being at risk. In addition, even though they produce the least amount of greenhouse gases, the people living in the worlds poorest countries will be the ones to suffer the most from the repercussions of climate change (Costello et al., 2009). African poor people are projected to lose healthy life years more than 500 times more than European nations as a result of global environmental change (Campbell-Lendrum et al., 2007).
Effects on urban forestry
One way to think about the urban forest, which in many respects is distinct from forests found in the countryside, is as the trees that are found in cities. In the context of forests, urban trees can be found in parks, along streets in rows, or even as individual trees. However, they are required to be in close pro-ximity to people who live in cities and structures that are built in cities. They differ in relation to com-position, age, health status, and ownership patterns. Urban trees have environmental, economic, and social values (Dwyer & Nowak, 2000; Ordóñez et al., 2010). The hydrological cycle is changing as a result of climate change, and this has an effect on urban forests. Winter precipitation increases the risk of physical damage to urban forests due to higher ice loading and snowfall. On the other hand, water scar-city is worsened during the summer months as a direct result of increased evapotranspiration. More-over, extreme events like cyclones, storm surges, and floods may damage urban forests (Safford et al., 2013). The capacity of forests to provide ecological services may be decreased, The capacity of forests to provide ecological services may be decreased, and the existence of urban forests and their composition can be affected as a result of the mentioned effects (Nowak, 2010; Ordóñez et al., 2010). For example, Hurricane Sandy, which hit New York City in October 2012 accompanied by high-speed winds and a storm surge, had a negative impact on urban green spaces and populations. Sandy uprooted and washed away 10,926 trees in New York City (Sutton, 2016).
Effects on urban tourism
One of the areas of the global economy that is grow-ing at the quickest rate is tourism, which is extre-mely susceptible to variations in regional weather and other aspects of the natural environment (Fang et al., 2018). However, this sector is in the enormously difficult position of being both a significant source of greenhouse gases and a substantial victim of cli-mate change. The impacts of climate change depend upon a destinations location, capacity, willingness, and readiness (Berrittella et al., 2006). Extreme events and environmental circumstances, including temperature variation, excessive or inadequate rain-fall, loss of ecological habitat, and infectious disea-ses, have an effect on resource-oriented attractions for tourists (Hall et al., 2004). The total number of visitors, duration of stay, trend of recreational acti-vities, destination preferences, customer satisfac-tion, operational cost, and even standards of safety and security in tourist areas are all likely to be influ-enced by the impacts of climate change on both a domestic and international scale (de Sherbinin et al., 2007; Gössling et al., 2006; Scott et al., 2008; Smith, 1990). For example, coastal cities like Rio de Janeiro that rely upon beach tourism may be affected by rising sea-levels combined with an increased frequ-ency and severity of destructive tidal waves. In Rio de Janeiro, coastal erosion brought on by sea-level rise increases operational costs (de Sherbinin et al., 2007). The number of tourists may decline as many cities are transforming their tourist sites because of the severe effects of flooding, heat waves, sea-level rise, storm surges, etc. (Buckley, 2012). Another study explored that the majority of tourists in tropi-cal regions, those who are spending their holidays in their own country or nearby, will change their desti-nations to mountainous areas to address climatic effects (Amelung et al., 2007).
Climate Change Mitigation-Adaptation
According to the Intergovernmental Panel on Cli-mate Change, mitigation is defined as "a human intervention to reduce the sources or enhance the sinks of greenhouse gases (GHGs)" while adaptation is defined as "the process of adjustment to actual or expected climate and its effects" (IPCC, 2014). In the context of urban planning, mitigation measures include in the energy sector: efficient energy consu-mption including energy savings lifestyle, renewable energy use, and smart technologies; the transport-tation sector: multi-modal, public, and hydroelectric-cally powered transportation; land use planning; building and infrastructure: building direction, height and spacing density of structure, multiple centers, mass transportation, non-motorized transportation including cycling and walking; and adaptation meas-ures include in building and infrastructure: space greening, green infrastructure, ventilation and air-conditioning; water management: blue spaces, flood protection embankments, polder, dams, etc (Grafa-kos et al., 2018; McEvoy et al., 2006). Spatial plan-ning is significantly important for implementing sev-eral measures for mitigation and adaptation and agreements formulated and signed at local, regional, and international levels. These strategies and agree-ments may be linked with land use pattern and land development, encouraging usage of non-fossil fuel energy, energy savings technology in building and transport systems, etc. for reducing the vulnerability of cities and neighborhoods (Davidse et al., 2015; Wang et al., 2018).
Urban form and structure
It is necessary to be prepared for the threats posed by climate change and to make plans for adaptation in light of the fact that the world population is becom-ing increasingly urbanized and concentrated. Beca-use of their highly urbanized and compact popula-tions as well as their urban structure, cities is acco-untable for 75% of the worlds emissions of green-house gases that are caused by the consumption of energy (Leibowicz, 2020; Wang et al., 2018). In order to devise solutions that are effective and trust-worthy for lowering emissions of greenhouse gases, it is necessary to have a solid understanding of the various urban shapes and structures. An effective urban form must instigate the development of green transportation, including mass transportation systems, hydroelectrically powered vehicles, walking, cycling, etc. (Dulal et al., 2011; Wang et al., 2018). How-ever, the building sector is responsible for 25% of global greenhouse gas emissions, particularly related to fossil fuel-based energy, mostly used for cooling and heating (Fosas et al., 2018; Schünemann et al., 2020). In this context, every new buildings biocli-matic architecture and layout, including the design of its site and direction, should be promoted to optimize the advantages of local environments, such as venti-lation and lighting. The creation of a green corridor would aid in the flow of air masses that enable cooling and ventilation processes within a compact urban form and structure (Yiannakou & Salata, 2017). Further, about 30% of energy consumption can be reduced by adding 5 cm of expanded poly-styrene and energy-efficient windows (Andric et al., 2020). Moreover, changes in urban form and stru-cture, including urban design, building materials, building structure, etc., significantly affect urban heat islands and urban climate (Emmanuel & Ferna-ndo, 2007; Hart & Sailor, 2009). At this size, the structure and spacing of dwellings in relation to one another, which mainly affect shading and wind speed, are physically expressed (Ramyar et al., 2019). Mixed-use development is the outcome of the spatial planning process and is referred to as the "complex developments" that take place in the public domain. Mixed-use planning aims to provide urban land-use with a mix of shopping, institutional, residential, recreational, and other functions clustered in one location, the same building, or adjacent to one ano-ther (Keeley & Frost, 2014; Raman & Roy, 2019; World Bank, 2014). One of the key benefits of mixed-use planning is that it promotes cycling and walking as modes of transportation. The effect of mixed-use on walking trips is greater than the vehi-cle miles traveled (VMT). Frank et al. (2011) found that mixed uses are strongly linked to both the number of miles driven and the amount of carbon di-oxide released.
Urban greening and green infrastructure practices
Urban greening has been conceptualized and pro-moted as a means of making communities more resi-lient in recent decades. In many cities across the world, the idea of urban greening has already been put into practice as a potential solution to the pro-blem of the urban heat islands (UHI) influence and as a method for lowering the greenhouse gases that are emitted. Urban greening may include street trees, urban parks, green walls, green roofs, etc. (Aram et al., 2019; Bowd et al., 2015; Grafakos et al., 2018; Kong et al., 2016; Norton et al., 2015). Another eco-system or environmental management approach, green infrastructure, is also one of the best strategic tools for both the adaptation and mitigation measures of climate change (Pauleit et al., 2013; Yiannakou & Salata, 2017). Green infrastructure, such as street trees, city parks, green corridors, and rooftops, imp-roves the quality of built environments in cities and provides resilience to climate extremes such as heat waves, droughts, and floods (Jamei & Tapper, 2018; Oke, 1989). The key advantages of urban greening and practices of green infrastructure are capturing and storing water; using it as carbon sinks; sustain-able ecosystems; neighborhood cooling; etc. (Aram et al., 2019; Jamei & Tapper, 2018; Yiannakou & Salata, 2017). Urban reforestation measures are being strongly advocated as a city planning strategy to off-set climate change, support human health, social well-being, and reduce environmental contamination exacerbated by urbanization (Salmond et al., 2016). Trees can influence wind behavior, including wind movement and velocity. This is, however, reliant on on the types of trees. Trees can enhance pedestrian or neighborhood thermal comfort (Bonan, 1997; Park et al., 2012; Shashua-Bar et al., 2011). About 30% to 40% of wind velocity can be reduced under the canopy of a deciduous tree (Oke, 1989). More-over, the presence of trees in the surrounding area can lower wind velocity by up to 51% (Park et al., 2012). Besides lowering wind speed, street trees help to increase air quality by absorbing air pollutants, airborne contaminants, and noise, reducing storm-water runoff, providing shade, and reducing the severity of the UHI effect (Ferrini et al., 2020; Sal-mond et al., 2016). Parks have the greatest cooling influence in city areas. However, the cooling effici-ency depends on park size, plant species, drainage capacity, etc. A study (Vaz Monteiro et al., 2016) found that large areas of green space (up to 12.1 ha) within 180 - 300 m of eight city center parks in London cool down by 1°C.
Forests serve as important carbon sinks, capturing and storing water, maintaining ecosystems, cooling neighborhoods, and protecting them from the waves of several natural disasters like cyclones, storm sur-ges, riverbank erosion, etc. (Bowd et al., 2015; Kole & Ellison, 2018; Valle Junior et al., 2015). Kole and Ellison, (2018) said that replanting trees in places where they have been cut down could help minimize the consequences of climate change. Green walls and rooftops help to combat climate change by acting as carbon sinks, controlling indoor temperatures, lowe-ring albedo, preserving local habitats and landscapes, and mitigating the severe effects of urban heat is-lands (Grafakos et al., 2018; Vijayara-ghavan, 2016). Morau et al. (2012) did a study on bituminous and green roofs on the island of Reunion in the Indian Ocean. They found that the maximum mean temperature on the bituminous roof was 73.5 ±1.4 °C, while on the green roof it was 34.8 ±0.6 °C. Green walls reduce cooling demand significantly in warm climates.
However, such walls may also serve as external insulation in cold weather. During the winter, green facades reduce heat loss across the building env-elope, lowering energy consumption. Hence, in all the above-mentioned cases, green walls contribute to reducing greenhouse gas emissions (Jamei & Tap-per, 2018). An average reduction of 4.4°C in surface temperature in the case of green facades compared to bare walls was investigated by a study carried out in Singapore (Wong et al., 2010). In the case of winter, green walls can save 20% of energy demand (Dje-djig et al., 2017).
Blue spaces
Urban "blue spaces" or waterbodies are the available surface water sources in an urban area, which com-prise ponds, lakes, rivers, canals, and streams. The provision of a thermally comfortable environment for city inhabitants is significantly aided by the pre-sence of blue spaces (Ampatzidis & Kershaw, 2020; Tominaga et al., 2015). The effects of climate change are starting to become apparent in the nations metro-politan water systems. Urban heat islands, extreme flooding or drought, storm incidence and severity, and sea-level rise are all having direct impacts on natural water supplies (Diaz & Yeh, 2014; Jamei & Tapper, 2018). Food processing, waste disposal, ele-ctricity generation, and a variety of other essential urban functions would all come to a halt if there were no surface waterbodies or blue spaces. Since cities now house the bulk of the worlds people, its critical that water providers take steps to address current and upcoming climate change challenges. Since 55% of the worldwide population lives in urban areas, it is of the utmost significance that urban planners take the steps needed to increase the amount of water available in surface areas to deal with climate change and associated consequences (Diaz & Yeh, 2014; Lv et al., 2020; United Nations, 2019). Blue spaces have the potential to diminish the thermal condition of their vicinity. However, this pot-ential varies based on their size, distribution pattern, and distance from the neighborhood. For example, a large single wetland has a greater cooling effect than many smaller and commonly shaped wetlands with the same total volume of water (Steeneveld et al., 2014). Further, blue spaces have a cooling capacity that is highly correlated with the local urban form and surface temperatures within a 500-meter radius (Cai et al., 2018). At a distance of ~30 m, blue spaces can produce a cooling effect of 1-3 °C (Klee-rekoper et al., 2012).
Moreover, blue spaces, particularly rivers, canals, and streams, may contribute to distributing spatial heat release (Hathway & Sharples, 2012).
Green Transportation
The transportation industry is a significant contri-butor to the release of greenhouse gases. In 2010, the final demand for energy associated with transport-ation contributed to 28% of the total end-use energy, with around 40% of that amount being consumed in urban transportation (Sims et al., 2014). Promoting non-fossil-fuel green transportation is viewed as a critical strategy for mitigating climate change (Kole & Ellison, 2018). Green transportation, which is also called "sustainable transformation," is a way to get around that is good for the environment and has a low carbon footprint. The implementation of environ-mentally friendly modes of transportation is bene-ficial for many reasons, including the effective use of existing road infrastructure, the sharp decline of traffic, the decrease in energy consumption, the improvement of air quality, and the enhancement of the general welfare of citizens (Li, 2016). For ex-ample, since 2013, more than 5,000 vehicles in Oslo, Norway, have been powered by hydroelectricity. Because of this, there have been fewer emissions of carbon dioxide, as well as improvements in air qua-lity and reductions in noise (Charan & Venkata-raman, 2017). Even though urban development has a limited effect on reducing greenhouse gas emissions in the short term because it takes time to build the necessary infrastructure, it has the potential to be very effective in the long term by shifting from a reliance on private vehicles to a reliance on public and other environmentally friendly forms of trans-portation, such as hydroelectrically powered vehi-cles, cycling, and walking (Dulal et al., 2011).
Strategies and frameworks
Cities are at the transition point between local policy and national-international agreements such as the UNFCCC, the Kyoto Protocol, and the Paris Agree-ment to adapt and mitigate climate change (Heidrich et al., 2016; Kuyper et al., 2018). Local, national, and international governments are working with cities to come up with and carry out actions and poli-cies regarding climate change. Climate policies and actions assist planners in developing integrated urban planning strategies that take into account multi-level urban governance approaches (Bulkeley, 2010; Gra-fakos et al., 2018; Pietrapertosa et al., 2018; Solecki et al., 2015). City councils may be the best at pro-tecting their communities from the current and future effects of climate change (Kole & Ellison, 2018). So, in 2018, almost 8,000 cities and other national and regional governments from every continent (except Antarctica) set goals to reduce greenhouse gas emi-ssions in their own communities (Grafakos et al., 2020). Spatial planning is becoming more important for meeting climate change goals because it helps reduce carbon dioxide emissions by making sure that land is used in a fair way. This is done by putting in place zoning laws to increase energy production, protect green spaces and infrastructure, and distri-bute land uses in a fair way (Wang et al., 2018). Spa-tial planning strategies and frameworks can adjust and reform urban form and structure in order to com-bat climate change (Wang et al., 2018). Hence, add-ressing the bottom-up approach, hundreds of cities and state councils have created and adopted muni-cipal climate action plans over the last few decades to tackle climate change (Sethi et al., 2020). In most European municipalities, urban planning is done in two stages: comprehensive spatial planning, which focuses on making a policy framework for the whole city, and site-specific detailed planning within the municipality, as well as the implementation of regu-latory instruments (Albrechts, 2004; Davidse et al., 2015).
Urbanization resulted from the increased use of fossil fuels and the release of greenhouse gases. By 2050, 68% of people will live in cities. This review identified the drivers and consequences of climate change in cities and the associated mitigation and adaptation measures. The urban population rose from 0.75 billion (1950) to 4.2 billion (2018), causing cli-mate change. Besides, rapid economic expansion in middle-income countries worsens carbon emissions. Urban form and design can also affect greenhouse gas emissions. Bitumen, pavement, and other hard sur-faces create urban heat islands. As the urban popu-lation continues to rise, cities are becoming denser and, in some cases, larger. It has been identified that nearly all Asian cities are vulnerable to flooding, cyclones, storm surges, heat waves, sea-level rise, excessive rainfall, drought, etc., and it is expected that extreme weather will double by 2050. Climate change has accelerated urbanization, population exp-ansion, and water demand, putting pressure on urban water sources. Similarly, it has a notable impact on urban forest hydrology. Furthermore, cyclones, storm surges, and floods can destroy urban forests and urban tourism. For mitigating and adapting to cli-mate change, spatial planning is crucial. To create effective plans, people must comprehend urban for-ms and design. The effective urban form must pro-mote green transportation, such as hydropower vehicles, walking, and cycling. In addition, mixed-use development combines retail, institutional, resi-dential, recreational, and other uses in one location or building. Urban greening may reduce the effects of urban heat islands. Blue spaces can reduce surro-unding temperatures. Green transportation is low-carbon and eco-friendly. Finally, cities take the lead in creating and executing climate actions and poli-cies to adapt and mitigate climate change. Therefore, in 2018, about 8,000 local, national as well as regi-onal governments from every continent (except Ant-arctica) set goals to reduce carbon emissions.
This study is part of the project “Integrating edu-cation with consumer behavior relevant to energy efficiency and climate change at the universities of Russia, Sri Lanka and Bangladesh (BECK)” and supported by grants from ERASMUS+ PROGRA-MME OF THE EUROPEAN UNION, grant number 598746-EPP-1-2018-LT-EPPKA2-CBHE-JP.
The authors declare no conflict of interest.
Academic Editor
Dr. Sonjoy Bishwas, Executive, Universe Publishing Group (UniversePG), California, USA.
Department of Land Record and Transformation, Patuakhali Science and Technology University, Bangladesh.
Siddik MA, Hasan MM, Islam MT, and Zaman AKMM. (2022). Climate change drivers, effects, and mitigation-adaptation measures for cities, Asian J. Soc. Sci. Leg. Stud., 4(5), 160-177. https://doi.org/10.34104/ajssls.022.01600177