Editing IPCC:AR6/WGII/Chapter-2 (section)

===== 2.5.1.3.2 Projections for freshwater biodiversity =====

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Because risk to freshwater species has been limited in past reports, this section provides details of freshwater risk. Lakes, rivers and freshwater wetlands cover approximately 7.7–9.1% of global land surface area; ( [[#Lehner--2008|Lehner et al., 2008]] ; [[#Fluet-Chouinard--2015|Fluet-Chouinard et al., 2015]] ; [[#Allen--2018|Allen and Pavelsky, 2018]] ) and hold 9.5% of the Earth’s described animals ( [[#Balian--2008|Balian et al., 2008]] ), with climate change indicated as a threat to 50–75% of fish ( [[#Xenopoulos--2005|Xenopoulos et al., 2005]] ; [[#Darwall--2015|Darwall and Freyhof, 2015]] ). Climate change is cited as a primary factor in species’ extinction risk due to changes in water temperatures, stream flow, loss of cold water habitat, increased variability of precipitation and increased disease risk from warming temperatures ( ''robust evidence'' , ''high agreement'' , ''high confidence'' ) ( [[#Knouft--2017|Knouft and Ficklin, 2017]] ; [[#Pletterbauer--2018|Pletterbauer et al., 2018]] ; [[#Jaric--2019|Jaric et al., 2019]] ; [[#Reid--2019|Reid et al., 2019]] ) adding to the stress of overexploitation and LULCC ( [[#Craig--2017|Craig et al., 2017]] ; [[#IPBES--2019|IPBES, 2019]] ).

Increased frequency of stream drying events, reducing hydrologic connectivity and limiting access of native fishes to spawning habitats is projected for RCP8.5 in Colorado, USA ( ''medium evidence'' , ''medium agreement'' ) ( [[#Jaeger--2014|Jaeger et al., 2014]] ). Cold-water habitats and associated obligate species are particularly vulnerable, and losses in these habitats have been both documented and projected, for example, in salmonids ( [[#Santiago--2016|Santiago et al., 2016]] ; [[#Fullerton--2017|Fullerton et al., 2017]] ; [[#Merriam--2017|Merriam et al., 2017]] ). River networks are projected to lose connections to cold tributary refugia, that are important thermal refuges for cold water species ( ''robust evidence'' , ''high agreement'' ) ( [[#Isaak--2016|Isaak et al., 2016]] ) during low flows ( [[#Merriam--2017|Merriam et al., 2017]] ).

Community turnovers are expected in freshwaters as cold-adapted species lose and warm-adapted species gain climatically suitable habitat ( [[#Domisch--2011|Domisch et al., 2011]] ; [[#Domisch--2013|Domisch et al., 2013]] ; [[#Shah--2014|Shah et al., 2014]] ). While a number of warm-adapted species may experience range expansions, the majority of species are predicted to lose climatically suitable areas by, on average, 38–44%, depending on the emission scenario (A2a and B2a) ( ''medium evidence'' ) ( [[#Domisch--2013|Domisch et al., 2013]] ).

Molluscs are projected to be the most at-risk group, given their limited dispersal capability ( [[#Woodward--2010|Woodward et al., 2010]] ). Mediterranean freshwater fish are especially susceptible to climate change due to increasing flood and drought events and the risk of surpassing critical temperature thresholds ( [[#Santiago--2016|Santiago et al., 2016]] ; [[#Jaric--2019|Jaric et al., 2019]] ). In southern Europe, aquatic insects (Ephemeroptera, Plecoptera and Trichoptera) are endangered by climate change ( [[#Conti--2014|Conti et al., 2014]] ). European protected areas are not expected to be sufficient under warming to provide habitat for the majority of rare molluscs and fish ( [[#Markovic--2014|Markovic et al., 2014]] ). Observed trends agree with model projections in direction, but magnitude remains uncertain ( ''medium evidence'' , ''medium agreement'' , ''medium confidence'' ) (see Figure 2.8 for extinction risk globally for dragonflies, amphibians and turtles).

Regional threats from climate change have been reported for 40% of amphibians in China, ( [[#Wu--2020|Wu, 2020]] ), 33% of European freshwater fish species ( [[#Janssen--2016|Janssen et al., 2016]] ) and 56–69% of odonates in Australia, ( [[#Bush--2014b|Bush et al., 2014b]] ). Assessment of site-specific extirpation for 88 aquatic insect taxa projected that climate change-induced hydrological alteration would result in a 30–40% loss of taxa in warmer, drier ecoregions and a 10–20% loss in cooler, wetter ecoregions ( ''medium evidence, medium agreement'' ) ( [[#Pyne--2017|Pyne and Poff, 2017]] ). In Africa’s Albertine Rift, 51% ( ''n'' = 551) of fish are expected to be impacted by climate change, with 5.5% at a high risk due to their sensitivity and poor adaptative capability ( ''medium evidence, high agreement'' ) ( [[#Carr--2013|Carr et al., 2013]] ).

The GLOBIO-Aquatic model ( [[#Janse--2015|Janse et al., 2015]] a) links models for demography, economy, LUCs, climate change, nutrient emissions, a global hydrological model and a global map of water bodies. It projects that changes in both water quality (eutrophication) and quantity (flow) will generate negative relations in freshwater ecosystems between the persistence of species originally present in each community and a constellation of stressors, including harmful algal blooms. Under a 4°C rise by 2050, mean abundance of species is projected to decline by 70% in running water and by 80% in standing water ( ''medium evidence'' , ''high agreement'' , ''medium confidence'' ) ( [[#Janse--2015|Janse et al., 2015]] a ).

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