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

=== 4.2.8 Observed Changes in Soil Erosion and Sediment Load ===

<div id="h2-10-siblings" class="h2-siblings"></div>

AR5 established potential impacts of climate change on soil erosion and sediment loads in mountain regions with glacier melt ( ''low to medium evidence'' ) ( [[#Jiménez%20Cisneros--2014|Jiménez Cisneros et al., 2014]] ). SRCCL (Olsson et al., 2020) reported with ''high confidence'' that rainfall changes attributed to human-induced climate change have already intensified drivers of land degradation. Nonetheless, attributing land degradation to climate change alone is challenging because of the role of land management practices ( ''medium evidence, high agreement'' ).

Climate change impacts soil erosion and sedimentation rates both directly from increasing rainfall or snowmelt intensity ( [[#Vanmaercke--2014|Vanmaercke et al., 2014]] ; [[#Polyakov--2017|Polyakov et al., 2017]] ; [[#Diodato--2018|Diodato et al., 2018]] ; [[#Golosov--2018|Golosov et al., 2018]] ; [[#Li--2020a|Li et al., 2020a]] ; [[#Li--2020b|Li et al., 2020b]] ) and indirectly from increasing wildfires ( [[#Gould--2016|Gould et al., 2016]] ; [[#Langhans--2016|Langhans et al., 2016]] ; [[#DeLong--2018|DeLong et al., 2018]] ), permafrost thawing ( [[#Schiefer--2018|Schiefer et al., 2018]] ; [[#Lafrenière--2019|Lafrenière and Lamoureux, 2019]] ; Ward [[#Jones--2019|Jones et al., 2019]] ) and vegetation cover changes ( [[#Micheletti--2015|Micheletti et al., 2015]] ; [[#Potemkina--2015|Potemkina and Potemkin, 2015]] ; [[#Carrivick--2017|Carrivick and Heckmann, 2017]] ; [[#Beel--2018|Beel et al., 2018]] ). In addition, accelerated soil erosion and sedimentation have severe societal impacts through land degradation, reduced soil productivity and water quality ( [[#4.2.7|Section 4.2.7]] ), increased eutrophication and disturbance to aquatic ecosystems ( [[#4.3.5|Section 4.3.5]] ), sedimentation of waterways and damage to infrastructure ( [[#Graves--2015|Graves et al., 2015]] ; [[#Issaka--2017|Issaka and Ashraf, 2017]] ; [[#Schellenberg--2017|Schellenberg et al., 2017]] ; [[#Hewett--2018|Hewett et al., 2018]] ; [[#Panagos--2018|Panagos et al., 2018]] ; [[#Sartori--2019|Sartori et al., 2019]] ) ( ''medium confidence'' ).

In the largest river basin of the Colombian Andes, regional climate change and land use activities (ploughing, grazing and deforestation) caused a 34% erosion rate increase over 10 years, with the anthropogenic soil erosion rate exceeding the climate-driven erosion rate ( [[#Restrepo--2018|Restrepo and Escobar, 2018]] ). Sedimentation increases due to soil erosion in mountainous regions burned by wildfires, as a result of warming and altered precipitation, is documented with ''high confidence'' in the USA ( [[#Gould--2016|Gould et al., 2016]] ; [[#DeLong--2018|DeLong et al., 2018]] ), Australia ( [[#Nyman--2015|Nyman et al., 2015]] ; [[#Langhans--2016|Langhans et al., 2016]] ), China ( [[#Cui--2014|Cui et al., 2014]] ) and Greece ( [[#Karamesouti--2016|Karamesouti et al., 2016]] ) and can potentially damage downstream aquatic ecosystems ( [[#4.3.5|Section 4.3.5]] ) and water quality ( [[#4.2.7|Section 4.2.7]] ) ( [[#Cui--2014|Cui et al., 2014]] ; [[#Murphy--2015|Murphy et al., 2015]] ; [[#Langhans--2016|Langhans et al., 2016]] ) ( ''medium confidence'' ). In Australia, for instance, sediment yields from post-fire debris flows (113–294 t ha –1 ) are 2–3 orders of magnitude higher than annual background erosion rates from undisturbed forests ( [[#Nyman--2015|Nyman et al., 2015]] ). The positive trend in sediment yield in small ponds in the semiarid southwestern USA over the last 90 years was not entirely related to the rainfall or runoff trends, but was a result of complex interaction between long-term changes in vegetation, soil and channel networks ( [[#Polyakov--2017|Polyakov et al., 2017]] ).

Regional climate changes (precipitation decrease) and human activities (landscape engineering, terracing, large-scale vegetation restoration, soil conservation) over the Loess Plateau (China) caused a distinct stepwise reduction in sediment loads from the upper-middle reach of the Yellow River, with 30% of the change related to climate change ( [[#Tian--2019|Tian et al., 2019]] ). Substantial increases in sediment flux were identified on the Tibetan Plateau ( [[#Li--2020a|Li et al., 2020a]] ; [[#Li--2021a|Li et al., 2021a]] ), for example, the sediment load from the Tuotuohe headwater increased by 135% from 1985–1997 to 1998–2016, mainly due to climate change ( [[#Li--2020a|Li et al., 2020a]] ). In 1986–2015, the sedimentation rate in dry valley bottoms of the Southern Russian Plain was two-2–5 times lower than in 1963–1986 due to the warming-induced surface runoff reduction during spring snowmelt ( [[#Golosov--2018|Golosov et al., 2018]] ). Declining erosion trends are primarily associated with soil conservation management in northern Germany ( [[#Steinhoff-Knopp--2018|Steinhoff-Knopp and Burkhard, 2018]] ) and reforestation in southwestern China ( [[#Zhou--2020|Zhou et al., 2020]] ).

The climate change impact on erosion and sediment load varies significantly over the world ( [[#Li--2020b|Li et al., 2020b]] ) ( ''high confidence'' ). There was a statistically significant correlation between sediment yield and air temperature for the non-Mediterranean region of western and central Europe ( [[#Vanmaercke--2014|Vanmaercke et al., 2014]] ) and northern Africa ( [[#Achite--2016|Achite and Ouillon, 2016]] ). Still, such correlation is yet to be found for the other European rivers ( [[#Vanmaercke--2015|Vanmaercke et al., 2015]] ). Increased sediment and particulate organic carbon fluxes in the Arctic regions are caused by permafrost warming ( [[#Schiefer--2018|Schiefer et al., 2018]] ; [[#Lafrenière--2019|Lafrenière and Lamoureux, 2019]] ; Ward [[#Jones--2019|Jones et al., 2019]] ). [[#Potemkina--2015|Potemkina and Potemkin (2015)]] demonstrate that regional warming and permafrost degradation have contributed to an increased forested area over the last 40–70 years, reducing soil erosion in eastern Siberia. The sediment dynamics of small rivers in the eastern Italian Alps, depending on extreme floods, is sensitive to climate change ( [[#Rainato--2017|Rainato et al., 2017]] ). In the northeastern Italian Alps, precipitation change during 1986–2010 affected soil wetness conditions, influencing sediment load ( [[#Diodato--2018|Diodato et al., 2018]] ). Regional warming in northern Africa (Algeria) dramatically changed river streamflow and increased sediment load over four decades (84% more every decade compared to the previous) ( [[#Achite--2016|Achite and Ouillon, 2016]] ).

A long-term global soil erosion monitoring network based on the unified methodological approach is needed to correctly evaluate erosion rates, detect their changes and attribute them to climate or other drivers.

In summary, in the areas with high human activity, factors other than climate have a more significant impact on soil erosion and sediment flux ( ''high confidence'' ). On the other hand, in natural conditions, for example, in high latitudes and high mountains, the influence of climate change on the acceleration of the erosion rate is observed ( ''limited evidence, medium agreement'' ).

<div id="4.3" class="h1-container"></div>

<span id="observed-sectoral-impacts-of-current-hydrological-changes"></span>