Editing IPCC:AR6/WGII/Chapter-16 (section)

===== 16.5.2.3.3 Risk to critical physical infrastructure and networks (RKR-C) =====

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RKR-C includes risks associated with the breakdown of physical infrastructure and networks which provide goods and services considered critical to the functioning of societies. It encompasses infrastructure systems for energy, water, transportation, telecommunications, health care and emergency response, as well as compound, cascading and cross-boundary risks resulting from infrastructure interdependencies ( [[#Birkmann--2016|Birkmann et al., 2016]] ; [[#Fekete--2019|Fekete, 2019]] ). Critical infrastructures such as transport or energy supply also play a central role in coping with climate risks, especially in acute disaster situations in which the services of transport infrastructure, communication technologies or electricity are particularly needed, despite the fact that these very systems are themselves exposed to disaster impacts ( [[#Garschagen--2016|Garschagen et al., 2016]] ; [[#Pescaroli--2018|Pescaroli et al., 2018]] ). The major hazards driving such risks are acute extreme events such as cyclones, floods, droughts or fires ( ''high confidence'' ), but cumulative and chronic hazards such as SLR are also considered.

RKR-C is considered severe when the functioning of critical infrastructure cannot be secured and maintained against climate change impacts, resulting in the frequent and widespread breakdown of service delivery and eventually a significant rise of detrimental impacts on people (lives, livelihoods and well-being), the economy (including averted growth) or the environment (disruption and loss of ecosystems) above historically observed levels. Severity in this RKR is assessed on two levels for (i) direct impacts of climate change on infrastructure assets and networks (e.g., amount of port infrastructure damaged or destroyed by SLR, flooding and storms) on which most of the literature focuses, as well as (ii) indirect and cascading downstream impacts to people, economy and environment ( [[#Markolf--2019|Markolf et al., 2019]] ; [[#Pyatkova--2019|Pyatkova et al., 2019]] ; [[#Chester--2020|Chester et al., 2020]] ), for which attribution is more difficult and uncertainties tend to be much higher. Overall, the literature with quantified assessments of climate change infrastructure risks remains to be less extensive than for many other risks, particularly with regard to assessments focusing on the Global South. While climate-related changes in hazards are widely considered in the literature, changes in future exposure and vulnerability conditions are often not treated explicitly. In addition, the severity of infrastructure risks also depends on future trends in the capacity to maintain, repair and rebuild infrastructure and adapt it to new hazard intensities ( ''medium evidence'' , ''high agreement'' ). These are mostly not quantified in a forward-looking manner in the literature; however, damage projections (see below) indicate a rapidly rising demand for investment, straining the financial capacity of countries ( ''medium evidence'' , ''high agreement'' ).

# Risks related to direct impacts on critical infrastructure would become severe with high warming, current infrastructure development regimes and minimal adaptation ( ''high confidence'' ), and in some contexts even with low warming, current vulnerability and no additional adaptation ( ''medium confidence'' ), with severity defined as infrastructure damage and required maintenance costs exceeding multiple times the current levels. Transport and energy infrastructure in coasts and polar systems and along rivers are projected to face a particularly steep rise in risk, resulting in severe risk even under medium warming ( ''high confidence'' ). Risk in relation to the increasing intensity and frequency of extreme events might become severe before the middle of the century ( ''medium confidence'' ). Damages from multiple climate hazards to transport, energy, industry and social infrastructure in Europe could increase 10-fold by the 2080s, from 3.4 € billion annually to date, and 15-fold for transport infrastructure, under Medium warming (A1B, ~3°C by 2100) and with current adaptation levels, even if no further extension of the infrastructure in exposed areas is considered ( [[#Forzieri--2018|Forzieri et al., 2018]] ). Under High warming (RCP8.5) in 2100, the percent of roads in the USA that require rehabilitation due to high temperatures and precipitation is expected to increase to 23–33%, relative to 14% in 2100 when no climate change is considered ( [[#Mallick--2018|Mallick et al., 2018]] ). Projections of climate-induced changes in exposure are an incomplete measure of risk but in the absence of other metrics can serve as a proxy for the potential for severe impacts. In the circumpolar Arctic, 14.8% of critical infrastructure assets would be affected by climate change under RCP8.5 by 2050, with lifecycle replacement costs projected to increase by 27.7% if infrastructure is to be preserved at current adaptation levels ( [[#Suter--2019|Suter et al., 2019]] ). Under RCP8.5, the number of ports under high risk will increase from 3.8% in the present day to 14.4% by 2100, as a result of increased coastal flooding and overtopping due to SLR, as well as the heat stress impacts of higher temperatures ( [[#Izaguirre--2021|Izaguirre et al., 2021]] ). In the UK under High warming (4°C), the number of clean and wastewater treatment sites located in the 1-in-75-year floodplain will increase by a third relative to today by the 2080s under current vulnerability and adaptation levels ( [[#Dawson--2018|Dawson et al., 2018]] ). A global assessment of changing climate and water resources for electricity generation finds considerable reductions in usable hydropower and thermoelectric capacity by 2050 for a range of warming scenarios from Low to High, with absolute declines on average for most (61–74%) of the world’s hydropower resources and monthly maximum reductions above 30% of usable capacity for over two-thirds of 1427 thermoelectric power plants worldwide ( [[#Van%20Vliet--2016|Van Vliet et al., 2016]] ). Many studies find large technical potential for coordinated adaptation–mitigation policies in the electricity sector to avoid a significant portion of projected climate change impacts (e.g., a two-thirds reduction, and in some cases fully offset) ( [[#Ciscar--2014|Ciscar and Dowling, 2014]] ; [[#Van%20Vliet--2016|Van Vliet et al., 2016]] ; [[#Gerlak--2018|Gerlak et al., 2018]] ; [[#Allen-Dumas--2019|Allen-Dumas et al., 2019]] ).
# Studies quantifying the indirect impacts of infrastructure failure on lives, livelihoods and economies are still rare but emerging, suggesting that risks would become severe in many contexts globally with high warming, current vulnerability and no additional adaptation ( ''medium confidence'' ). Severity in this context is defined as the potential to disrupt the lives, livelihoods and well-being of a significantly increased proportion of the population and to significantly forestall economic growth and development potential. Global risks to air travel from SLR, expressed in terms of expected annual route disruptions, could increase by a factor of between 17 and 69 by 2100 under the 1.5°C and the 95th percentile value of the RCP8.5 SLR scenario, respectively ( [[#Yesudian--2021|Yesudian and Dawson, 2021]] ). By 2050, up to 185,000 airline passengers per year may be grounded due to extreme heat (48°C) if no additional adaptation is taken, roughly 23 times more than today ( [[#McKinsey%20Global%20Institute--2020|McKinsey Global Institute, 2020]] ). In Africa, under RCP8.5 and without additional adaptation, a 250% increase in disruption time of the transport network is expected by 2050 due to extreme temperatures, a 76% increase due to precipitation, and 1400% increase due to flooding ( [[#Cervigni--2015|Cervigni et al., 2015]] ). On the Dawlish railway section (UK), the number of days with line restrictions is set to increase by up to 1170%, to as high as 84–120 yr –1 by 2100 due to 0.8 m SLR with High warming ( [[#Dawson--2016|Dawson et al., 2016]] ). Next to the limited number of projections or scenarios of indirect impacts, additional inferences from studies focusing on past and current impacts can be drawn. Already today, climate-related impacts on transport and energy infrastructure reach far beyond the direct impacts on physical infrastructure, triggering indirect impacts on, for example, health and income ( ''medium confidence'' ). A case study of future flood hazard in Europe found that the indirect impact of a power outage on the local economy is six to eight times greater than the direct flood damage and asset repair costs, due to the interruption of daily economic activity ( [[#Karagiannis--2019|Karagiannis et al., 2019]] ). In low- and middle-income countries, the annual costs from infrastructure disruptions reach up to 300 billion USD for firms and 90 billion USD for private households, with natural hazards such as floods being responsible for 10–70% of these disruptions, depending on the sectors and regions ( [[#Hallegatte--2019|Hallegatte et al., 2019]] ). Power outages triggered by floods or droughts have also been found to have substantial health implications, particularly among low-income populations ( [[#Klinger--2014|Klinger et al., 2014]] ), and shown to impede disaster recovery efforts and severely disrupt local economies ( [[#Karagiannis--2019|Karagiannis et al., 2019]] ; [[#Nicolas--2019|Nicolas et al., 2019]] ). In addition, risks associated with infrastructure have the potential to become particularly severe when hazard-driven infrastructure disruptions undermine the capacity of emergency response in disaster situations ( ''limited evidence'' , ''high agreement'' ). A study on the UK shows, for example, that even a small increase in minor road flooding leads to a disproportionately high disruption of the efficacy of emergency services ( [[#Yu--2020|Yu et al., 2020]] ). Similar risks have been found for rural areas, particularly in developing countries ( [[#Alegre--2020|Alegre et al., 2020]] ).

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