Editing IPCC:AR6/WGII/Chapter-18 (section)

==== 18.3.1.2 Urban and Infrastructure Systems ====

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Urban areas and their associated infrastructure are critical targets for CRD processes. This is a function of urban areas being the dominant settlement pattern, with over 55% of the global population living in cities ( [[#World%20Bank--2021|World Bank, 2021]] ). As a consequence, urban areas are also the focal point for energy use, land use change and consumption of natural resources, thereby making them responsible for an estimated 70% of global CO 2 emissions ( [[#Johansson--2012|Johansson et al., 2012]] ; [[#Ribeiro--2019|Ribeiro et al., 2019]] ). The trend towards increasing urbanisation is anticipated to create both challenges and opportunities for sustainable development, as well as climate action ( [[#Güneralp--2017|Güneralp et al., 2017]] ; [[#Li--2019a|Li et al., 2019a]] ).

The built environment is increasingly exposed to climate stresses and more frequent co-occurrences of climate shocks than in the past. This has the potential to increase rates of building and infrastructure degradation and increase damage from extreme weather events. The existing adaptation gaps and everyday risks within many cities, particularly those of the Global South, combined with escalating risk from climate change, makes rapid progress in enhancing urban resilience a high priority for CRD ( [[#Pelling--2018|Pelling et al., 2018]] ; [[#Davidson--2019|Davidson et al., 2019]] ; [[#Lenzholzer--2020|Lenzholzer et al., 2020]] ). Strategic investments in disaster risk reduction, including climate-resilient green infrastructure, updated building codes and land use planning can provide significant long-term cost savings and social benefits. Moreover, evaluating the relative merits of ‘fail safe’ versus ‘safe to fail’ approaches to infrastructure planning can help to identify more design principles that are more robust to the uncertainties of climate change and urbanisation ( [[#Kim--2017a|Kim et al., 2017a]] ; [[#Kim--2019|Kim et al., 2019]] ).

Much of the literature on urban resilience and sustainability focuses on addressing discrete challenges for urban infrastructure subsystems. Climate change has the potential to enhance stress on lifeline infrastructure services such as the provision of electricity, water and wastewater, communications and transportation—subsystems which are often underdeveloped in many regions of the world ( [[#Arku--2021|Arku and Marais, 2021]] ; [[#Sitas--2021|Sitas et al., 2021]] ). For example, a warming and more variable climate can increase stress on electricity grids by reducing transmission efficiency, increasing cooling demand requirements, and by increasing exposure to climate shocks such as heatwaves, floods and storms ( [[#Bartos--2015|Bartos and Chester, 2015]] ; [[#Auffhammer--2017|Auffhammer et al., 2017]] ; [[#Perera--2020|Perera et al., 2020]] ). Accordingly, a significant focus on the energy transition is on achieving the dual goals of reducing the carbon footprint of energy while also increasing resilience of energy supply to current and future threats. For example, renewable energy generation and storage technologies that are modular and distributed and provide enhanced resilience to shocks and stresses from climate change (Venema and [[#Temmer--2017a|Temmer, 2017a]] ).

Similarly, building and maintaining urban water systems that are resilient to climate shocks requires significant changes in water demand, infrastructure and management. Enhancing redundancy in water supply and the flexibility to shift between surface and groundwater options aids adaptation. Decentralised water supply and sanitation options are now feasible and can provide greater resilience than most centralised systems ( [[#Parry--2017|Parry, 2017]] ), provided they have adequate supply ( [[#Leigh--2019|Leigh and Lee, 2019]] ; [[#Rabaey--2020|Rabaey et al., 2020]] ). Water conservation and green infrastructure options for stormwater management are proven approaches for reducing climate risks (Venema and [[#Temmer--2017b|Temmer, 2017b]] ), with adaptation and mitigation co-benefits. Water demand management and rainwater harvesting contribute to climate change mitigation and increase adaptive capacity by increasing resilience to climate change impacts such as drought and flooding ( [[#Paton--2014|Paton et al., 2014]] ; [[#Berry--2015|Berry et al., 2015]] ). In addition, they can contribute to restoring urban ecosystems that offer multiple ecosystem services to citizens ( [[#Berry--2015|Berry et al., 2015]] ) {Lwasa, 2022 #4317} . The context-appropriate development of green spaces, protecting ecosystem services and developing nature-based solutions, can increase the set of available urban adaptation options ( [[#IPCC--2018b|IPCC, 2018b]] ), while creating opportunities for more complex and dynamic approaches to urban water management ( [[#Franco-Torres--2020|Franco-Torres et al., 2020]] ). For example, the Netherlands’ ‘Room for the River’ policy focuses on not only achieving higher flood resilience, but also improving the quality of riverine areas for human and ecological well-being ( [[#Busscher--2019|Busscher et al., 2019]] ).

An overarching focus of urban sustainability is the reversal of long-standing trends of ecosystem fragmentation and degradation that have resulted in growing separation between human and natural systems within urban environments ( [[#IPBES--2019|IPBES, 2019]] ) (Lwasa et al., 2022). Urban ecosystems and the integration of nature-based solutions and green infrastructure into urban areas can yield benefits that facilitate achievement of the SDGs. There has been growing recognition of urban ecosystems as social, cultural and economic assets that can support economic development while also enhancing resilience to extreme weather events and improving air and water quality ( [[#Shaneyfelt--2017|Shaneyfelt et al., 2017]] ; [[#Matos--2019|Matos et al., 2019]] ). Investing in urban ecosystems and green infrastructure can provide lower-cost solutions to multiple urban development challenges when compared with traditional infrastructure systems ( [[#Terton--2017|Terton, 2017]] ). Relatedly, agriculture, while largely a rural system, is increasingly expanding within urban areas. Urban agriculture enables citizens to fulfil some of their food needs, improving urban resilience to food shortages, enhancing biodiversity and increasing coping capacity during disasters ( [[#Demuzere--2014|Demuzere et al., 2014]] ; [[#Clucas--2018|Clucas et al., 2018]] ) (Lwasa et al., 2022). Strengthening urban agroecosystems therefore increases resilience to supply shocks from climate change impacts and can contribute to community cohesion ( [[#Temmer--2017a|Temmer, 2017a]] ).

Overall, the discourse in the literature regarding the future of cities emphasises the importance of viewing cities as more than just their physical infrastructure that can be made more resilient through engineering solutions ( [[#Davidson--2019|Davidson et al., 2019]] ). Rather, urban areas are increasingly conceptualised as complex socio-ecological or socio-technical systems ( ''very high confidence'' ) ( [[#Patorniti--2017|Patorniti et al., 2017]] ; [[#Patorniti--2018|Patorniti et al., 2018]] ; [[#Visvizi--2018|Visvizi et al., 2018]] ; [[#Savaget--2019|Savaget et al., 2019]] ). Such frameworks integrate physical, cyber, social and ecological elements of cities in pursuit of resilience and sustainability transitions, and they recognise the role of governance and engagement processes as being central to system change ( [[#Temmer--2017b|Temmer, 2017b]] ). Nevertheless, some authors have cautioned that urban transitions will be associated with synergies as well as trade-offs with respect to sustainable development ( ''very high confidence'' ) ( [[#Maes--2019|Maes et al., 2019]] ; [[#Sharifi--2020|Sharifi, 2020]] ).

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