Editing IPCC:AR6/WGII/Chapter-4 (section)

=== 4.3.2 Observed Impacts on Energy and Industrial Water Use ===

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AR5 ( [[#Jiménez%20Cisneros--2014|Jiménez Cisneros et al., 2014]] ) concluded with ''medium evidence'' and ''high agreement'' that hydropower negatively impacts freshwater ecosystems. SROCC ( [[#IPCC--2019a|IPCC, 2019a]] ) concluded with ''medium confidence'' that climate change has led to both increases and decreases in annual/seasonal water inputs to hydropower plants.

Water is a crucial input for hydroelectric and thermoelectric energy production, which together account for 94.7% of the world’s current electricity generation ( [[#Petroleum--2020|Petroleum, 2020]] ). Climate change impacts hydropower production through changes in precipitation, evaporation, volume and timing of runoff; and impacts cooling of thermoelectric power plants through reduced streamflow and increased water temperatures ( [[#Yalew--2020|Yalew et al., 2020]] ). In addition, extreme weather events, like tropical cyclones, landslides and floods, damage energy infrastructure ( [[#MCTI--2020|MCTI, 2020]] ; [[#Yalew--2020|Yalew et al., 2020]] ), while high temperature and humidity increase the energy requirement for cooling ( [[#Maia-Silva--2020|Maia-Silva et al., 2020]] ).

With 1308 GW installed capacity in 2019, hydropower became the world’s largest single source of renewable energy ( [[#IHA--2020|IHA, 2020]] ) (also see Figure 6.12, WGIII). While hydropower reduces emissions relative to fossil fuel-based energy production, hydropower reservoirs are being increasingly associated with GHG emissions caused by submergence and later re-emergence of vegetation under reservoirs due to water level fluctuations ( [[#Räsänen--2018|Räsänen et al., 2018]] ; [[#Song--2018|Song et al., 2018]] ; [[#Maavara--2020|Maavara et al., 2020]] ). A recent global study concluded that reservoirs might emit more carbon than they bury, especially in the tropics ( [[#Keller--2021|Keller et al., 2021]] ) ( ''medium confidence'' ).

In Ghana, between 1970 and 1990, rainfall variability accounted for 21% of interannual variations in hydropower generation ( [[#Boadi--2019|Boadi and Owusu, 2019]] ). In Brazil’s São Francisco River, following drought events in 2016 and 2017, hydropower plants operated with an average capacity factor of only 23% and 17%, respectively ( [[#de%20Jong--2018|de Jong et al., 2018]] ). In Switzerland, increased glacier melt contributed to 3–4% of hydropower production since 1980 ( [[#Schaefli--2019|Schaefli et al., 2019]] ) ( [[#4.2.2|Section 4.2.2]] ). In the USA, hydropower generation dropped by nearly 27% for every standard deviation increase in water scarcity. Equivalent social costs of loss in hydropower generation between 2001 and 2012 were approximately USD 330,000 (at 2015 value) per month for every power plant that experienced water scarcity ( [[#Eyer--2018|Eyer and Wichman, 2018]] ). Globally, for the period 1981–2010, the utilisation rate of hydropower was reduced by 5.2% during drought years compared to long-term average values ( [[#van%20Vliet--2016a|van Vliet et al., 2016a]] ). Thus, there is a growing body of evidence of negative impacts of extreme events on hydropower production ( ''high confidence'' ).

Impacts of water scarcity on thermoelectric plants are more unequivocal than hydropower plants. For example, a scenario-based simulation study showed that 32% of the world’s coal-fired power plants (CFPPs) plants are currently experiencing water scarcity for at least five months or more in a year ( [[#Rosa--2020c|Rosa et al., 2020c]] ). In the UK, almost 50% of freshwater thermal capacity is lost on extreme high-temperature days, causing losses in the range of average GBP 29–66 million yr –1 . For ~20% of particularly vulnerable power plants, these losses could increase to GBP 66–95 million yr –1 annualised over 30 years ( [[#Byers--2020|Byers et al., 2020]] ). Globally, for the period 1981–2010, the utilisation rate of thermoelectric power was reduced by 3.8% during drought years compared to long-term average values ( [[#van%20Vliet--2016a|van Vliet et al., 2016a]] ), and none of the studies reported increases in thermoelectric power production as a consequence of climate change ( ''high confidence'' ).

In the energy sector, a large number of studies document the impact of extreme climate events (e.g., droughts or extreme temperature days) on production of hydropower and thermoelectric power, yet there are limited studies that measure trends in energy production due to long-term climate change. This remains a knowledge gap.

Mining in regions already vulnerable to climate change-induced water scarcity is under threat, leading some countries like El Salvador to ban metal mining completely ( [[#Odell--2018|Odell et al., 2018]] ). Likewise, food and agro-processing companies are aware of water-related threats to their operations, with 77% of 35 publicly traded companies evaluated in 2019 explicitly citing water as a risk factor in their annual reports, up from 59% in 2017 ( [[#CDP--2018|CDP, 2018]] ; [[#CERES--2019|CERES, 2019]] ). Changes in water availability affect the mining, electrical, metal and agro-processing sectors ( [[#UNIDO--2017|UNIDO, 2017]] ; [[#Odell--2018|Odell et al., 2018]] ; [[#Frost--2019|Frost and Hua, 2019]] ), but these impacts are less understood due to the lack of studies.

In summary, there is ''high confidence'' that climate change has had negative impacts on hydro and thermal power production globally due to droughts, changes in the seasonality of river flows, and increasing ambient water temperatures.

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