Editing IPCC:AR6/WGII/Cross-Chapter-Paper-5 (section)

=== CCP5.3.1 Synthesis of Projected Impacts ===

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Declines and extinctions have been projected in a range of montane plants and animal species, including rare endemic species and sub-species due to climate change ( ''medium evidence, high agreement'' ) ( [[#Li--2017|Li et al., 2017]] ; [[#Ashrafzadeh--2019|Ashrafzadeh et al., 2019]] ; [[#Brunetti--2019|Brunetti et al., 2019]] ; [[#Zhang--2019b|Zhang et al., 2019b]] ; [[#Manes--2021|Manes et al., 2021]] ). Up to 84% of endemic mountain species are found to be at risk of extinction ( [[#Manes--2021|Manes et al., 2021]] ). Using a simple model, [[#Helmer--2019|Helmer et al. (2019)]] predict a large-scale contraction in the next 25 years of alpine ecosystems above tropical mountain cloud forest in the Andes due to tree invasion. Topographic complexity can smoothen and delay the transition of montane forests in terms of size and composition for warming up to 3°C GWL ( [[#Albrich--2020|Albrich et al., 2020]] ).

Hydrological changes will determine how some ecosystems change, more so than changes in temperature. For example, Dwire et al. (2018) found that changes in riparian areas, wetlands and forests were likely a result of climate change in the Blue Mountains in Oregon, USA, as a result of altered snowpack, hydrologic regimes, drought and wildfire. In the Bolivian Cordillera Real, wetland cover variations were associated with increases in extreme precipitation events and glacier melting over the 1984–2011 period but might be reversed with predicted future decreases in both total precipitation and glacier run-off ( [[#Dangles--2017|Dangles et al., 2017]] ). About 30% of the wetland area in the Great Xing’an Mountains in northeastern China has been projected to disappear by 2050, with this value doubling by 2100 under the CGCM3-B1 scenario ( [[#Liu--2011|Liu et al., 2011]] ).

Climate change impacts on food, fibre and ecosystem products will be highly variable across mountain regions ( ''medium confidence'' ) ( [[#Briner--2013|Briner et al., 2013]] ; [[#Rasul--2015|Rasul and Hussain, 2015]] ; [[#Mina--2017|Mina et al., 2017]] ; [[#Palomo--2017|Palomo, 2017]] ; [[#Said--2019|Said et al., 2019]] ; [[#Xenarios--2019|Xenarios et al., 2019]] ) (Sections 10.4, 12.3, 13.5 and 14.4). In some regions, tree crops that are cultivated at certain elevations may reach the limit of their agroclimatic plasticity, for instance for crop types that require winter chills and where projected growing conditions are too warm ( [[#Buerkert--2020|Buerkert et al., 2020]] ). In the European Alps, agricultural production in some areas may benefit from temperature rises, as total productivity in grasslands is projected to increase ( [[#Mitter--2015|Mitter et al., 2015]] ; [[#Grüneis--2018|Grüneis et al., 2018]] ), whereas some areas in Asia and South America heavily dependent on glacier- and snow-fed irrigation will be at risk of food insecurity ( [[#Rasul--2019|Rasul and Molden, 2019]] ). In a study in Eastern Pamir, [[#Mętrak--2017|Mętrak et al. (2017)]] found that summer droughts and water changes lead to functional transformations of the wetland ecosystems which can affect food security of the local population. Climate change affects the phenology of plants ( [[#Harish--2012|Harish et al., 2012]] ; [[#Gaira--2014|Gaira et al., 2014]] ; [[#Maikhuri--2018|Maikhuri et al., 2018]] ), secondary metabolites ( [[#Chang--2016|Chang et al., 2016]] ; [[#Kumar--2020|Kumar et al., 2020]] ) and pharmacological properties of medicinal plants ( [[#Gairola--2010|Gairola et al., 2010]] ; [[#Das--2016|Das et al., 2016]] ).

Water resources in mountains and dependent lowlands will continue to be strongly impacted by climate change throughout the 21st century ( ''high confidence'' ). The difference in impacts will be particularly strong in regions that greatly depend on glacier and snowmelt and, in pronounced dry seasons ( ''high confidence'' ), in regions including Central Asia, South Asia, tropical and subtropical western South America and southwestern North America ( [[#Huss--2018|Huss and Hock, 2018]] ; [[#Hock--2019|Hock et al., 2019]] ; [[#Immerzeel--2020|Immerzeel et al., 2020]] ). Glaciers are expected to continue to lose mass throughout the 21st century, with higher mass loss under high emission scenarios (AR6 WGI [[IPCC:Wg2:Chapter:Chapter-9|Chapter 9]] ( [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] )). Many low-elevation and small glaciers around the world will lose most of their total mass at 1.5°C GWL ( ''high confidence'' ) ( [[#Marzeion--2018|Marzeion et al., 2018]] ; [[#Vuille--2018|Vuille et al., 2018]] ; [[#Hock--2019|Hock et al., 2019]] ; [[#Zekollari--2020|Zekollari et al., 2020]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ) (WGI 9.5). For tropical and mid-latitude mountains, around half of the current ice mass can be preserved under low-emission scenarios, while between two-thirds and up to more than 90% will be lost under high emission scenarios compared to the 2000s ( ''medium confidence'' ) ( [[#Schauwecker--2017|Schauwecker et al., 2017]] ; [[#Vuille--2018|Vuille et al., 2018]] ; [[#Hock--2019|Hock et al., 2019]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ) (WGI 9.5). Significant differences in impacts between the emission scenarios have also been assessed for declines in snow depth or mass at lower elevations [10 to 40% for RCP2.6 and 50 to 90% for RCP 8.5 by the end of the century ( [[#Hock--2019|Hock et al., 2019]] )]. However, limitations in long-term climate, glaciological and hydrological monitoring data add uncertainty to the current understanding and adaptation support, for example, when peak water is reached in different mountain catchments ( [[#Salzmann--2014|Salzmann et al., 2014]] ; [[#Hock--2019|Hock et al., 2019]] ). Furthermore, context-specific sociocultural and economic factors can magnify or moderate impacts related to hydrological change ( [[#McDowell--2021a|McDowell et al., 2021a]] ).

The dependence of lowland populations on mountain water resources will grow by mid-century across several climate and socioeconomic scenarios, and several seasonally dry or semiarid mountain regions (e.g., parts of South Asia, North America) are projected to be highly dependent on such resources ( ''medium confidence'' ) ( [[#Viviroli--2020|Viviroli et al., 2020]] ) (Figure CCP5.2). Changing sediment, nutrient and pollutant flows due to climatic and non-climatic drivers will impact populations and economic sectors ( ''medium evidence, high agreement'' ). Hydropower in all mountain regions will experience higher fluxes of water and sediment in some seasons but lower water flow with demand from other water uses (e.g., irrigation) ( [[#Chevallier--2011|Chevallier et al., 2011]] ) in other seasons ( [[#Beniston--2014|Beniston and Stoffel, 2014]] ; [[#Gaudard--2014|Gaudard et al., 2014]] ; [[#Majone--2016|Majone et al., 2016]] ; [[#Caruso--2017a|Caruso et al., 2017a]] , b; [[#Patro--2018|Patro et al., 2018]] ). Recharge from groundwater and its buffer function is expected to decrease in the longer term ( [[#Somers--2020|Somers and McKenzie, 2020]] ). Glacier and snow depth or mass decline will impact current hydropower facilities and production in various complex ways, requiring changes in hydropower management, with further potential for evidence-informed solutions ( [[#Gaudard--2014|Gaudard et al., 2014]] ; [[#Schaefli--2015|Schaefli, 2015]] ; [[#Schaefli--2019|Schaefli et al., 2019]] ). On the other hand, deglaciation in mountain regions opens topographic space and, thus, potential for additional long-term hydropower development and production ( [[#Haeberli--2016a|Haeberli et al., 2016a]] ), with an estimated additional production of up to several hundred terawatt-hours per year, a potentially important contribution to national energy supplies, in particular in the High Mountain Asia region ( [[#Farinotti--2019|Farinotti et al., 2019]] ). However, water supply from glacier melt will decrease once source glaciers pass peak discharge ( [[#Huss--2018|Huss and Hock, 2018]] ), and the areas with available sediment will grow as glaciers shrink, posing potential risks to downstream populations and assets ( ''high confidence'' ) ( [[#Lane--2019|Lane et al., 2019]] ).

Since SROCC ( [[#Hock--2019|Hock et al., 2019]] ), several new studies have addressed projected impacts of future climate change on snow reliability in ski resorts, complementing previous findings or bridging existing knowledge gaps for winter tourism. This includes, in particular, new studies for China (An et al., 2019; [[#Fang--2019|Fang et al., 2019]] ), showing that average ski seasons are projected to shorten (−4 to −61% for RCP4.5; −6 to −79% RCP8.5 in the 2050s) along with increases in snow-making water demand (27 to 51% for RCP4.5; 46 to 80% for RCP8.5 in the 2050s), with large differences across the country. Changes in future snow reliability are projected across Europe at the national or pan-European scale ( [[#Demiroglu--2019|Demiroglu et al., 2019]] ; [[#Steiger--2020|Steiger and Scott, 2020]] ; [[#Morin--2021|Morin et al., 2021]] ), highlighting strong contrasts at the local (across ski resort size and/or elevation range, or local social or environmental context) and continental scales. Higher-latitude and high-elevation locations generally exhibit delayed declines in snow reliability compared to lower-latitude and lower-elevation locations ( ''high confidence'' ), consistent with assessment conclusions reached in SROCC ( [[#Hock--2019|Hock et al., 2019]] ). In general, climate change impacts and risks to ski tourism are found to be spatially heterogeneous, within and across local and international markets, with potential for significant disruptions to related socioeconomic sectors due to a growing mismatch between ski area supply and skier demand in the coming decades ( ''high confidence'' ) ( [[#Fang--2019|Fang et al., 2019]] ; [[#Hock--2019|Hock et al., 2019]] ; [[#Steiger--2021|Steiger et al., 2021]] ). These disruptions are plausible, even though a fraction of current ski resorts could technically operate in comparatively favourable locations (elevation, latitude) and operating models (business models, sociocultural assets and conditions, governance) ( [[#Steiger--2020|Steiger et al., 2020]] ).

Severe damage and disruptions to people and infrastructure from floods are projected to increase in Northwestern South America (NWS), South Asia (SAS), Tibetan Plateau (TIB) and Central Asia (WCA) between 1.5°C and 3°C GWL, mainly driven by river floods and an increase in the number of glacial lakes with high potential for outburst ( ''high confidence'' ) ( [[#Drenkhan--2019|Drenkhan et al., 2019]] ; [[#Motschmann--2020b|Motschmann et al., 2020b]] ; [[#Furian--2021|Furian et al., 2021]] ; [[#Zheng--2021|Zheng et al., 2021]] ). For example, the formation of new lakes at the foot of steep icy peaks largely extends the hazard zones with respect to the earlier situation without lakes ( [[#Haeberli--2016b|Haeberli et al., 2016b]] ). Projected changes in ice and snowmelt, as well as seasonal increases in extreme rainfall and permafrost thaw, will favour chain reactions and cascading processes, which can have devastating downstream effects well beyond the site of the original event ( ''high confidence'' ) ( [[#Cui--2015|Cui and Jia, 2015]] ; [[#Beniston--2018|Beniston et al., 2018]] ; [[#Terzi--2019|Terzi et al., 2019]] ; [[#Vaidya--2019|Vaidya et al., 2019]] ; [[#Shugar--2021|Shugar et al., 2021]] ). The incidence of disasters is projected to increase in the future because some hazards will become more pervasive, with an increase in the exposure of people and infrastructure with future environmental and socioeconomic changes either contributing to reduce or enhance these disaster risks ( ''medium confidence'' ) ( [[#Klein--2019b|Klein et al., 2019b]] ).

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