Editing IPCC:AR6/SRCCL/Chapter-3 (section)

=== 3.7.1 Climate change and soil erosion ===

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==== 3.7.1.1 Soil erosion under changing climate in drylands ====

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Soil erosion is a major form of desertification occurring in varying degrees in all dryland areas across the world (Section 3.2), with negative effects on dryland ecosystems (Section 3.4). Climate change is projected to increase soil erosion potential in some dryland areas through more frequent heavy rainfall events and rainfall variability (see Section 3.5.2 for a more detailed assessment) (Achite and Ouillon 2007 <sup>[[#fn:r1500|1500]]</sup> ; Megnounif and Ghenim 2016 <sup>[[#fn:r1501|1501]]</sup> ; Vachtman et al. 2013 <sup>[[#fn:r1502|1502]]</sup> ; Zhang and Nearing 2005 <sup>[[#fn:r1503|1503]]</sup> ). There are numerous soil conservation measures that can help reduce soil erosion (Section 3.6.1). Such soil management measures include afforestation and reforestation activities, rehabilitation of degraded forests, erosion control measures, prevention of overgrazing, diversification of crop rotations, and improvement in irrigation techniques, especially in sloping areas (Anache et al. 2018 <sup>[[#fn:r1504|1504]]</sup> ; ÇEMGM 2017; Li and Fang 2016; Poesen 2018 <sup>[[#fn:r1505|1505]]</sup> ; Ziadat and Taimeh 2013 <sup>[[#fn:r1506|1506]]</sup> ). Effective measures for soil conservation can also use spatial patterns of plant cover to reduce sediment connectivity, and the relationships between hillslopes and sediment transfer in eroded channels (García-Ruiz et al. 2017 <sup>[[#fn:r1507|1507]]</sup> ). The following three examples present lessons learnt from the soil erosion problems and measures to address them in different settings of Chile, Turkey and the Central Asian countries.

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==== 3.7.1.2 No-till practices for reducing soil erosion in central Chile ====

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Soil erosion by water is an important problem in Chile. National assessments conducted in 1979, which examined 46% of the continental surface of the country, concluded that very high levels of soil erosion affected 36% of the territory. The degree of soil erosion increases from south to north. The leading locations in Chile are the region of Coquimbo with 84% of eroded soils (Lat. 29°S, semi-arid climate), the region of Valparaíso with 57% of eroded soils (Lat. 33°S, Mediterranean climate) and the region of O’Higgins with 37% of eroded soils (Lat. 34°S, Mediterranean climate). The most important drivers of soil erosion are soil, slope, climate erosivity (i.e., precipitation, intensity, duration and frequency) due to a highly concentrated rainy season, and vegetation structure and cover. In the region of Coquimbo, goat and sheep overgrazing have aggravated the situation (CIREN 2010 <sup>[[#fn:r1508|1508]]</sup> ). Erosion rates reach up to 100 t ha <sup>–1</sup> annually, having increased substantially over the last 50 years (Ellies 2000). About 10.4% of central Chile exhibits high erosion rates (greater than 1.1 t ha <sup>–1</sup> annually) (Bonilla et al. 2010 <sup>[[#fn:r1509|1509]]</sup> ).

Over the last few decades there has been an increasing interest in the development of no-till (also called zero tillage) technologies to minimise soil disturbance, reduce the combustion of fossil fuels and increase soil organic matter. No-till, in conjunction with the adoption of strategic cover crops, has positively impacted soil biology with increases in soil organic matter. Early evaluations by Crovetto, (1998) showed that no-till application (after seven years) had doubled the biological activity indicators compared to traditional farming and even surpassed those found in pasture (grown for the previous 15 years). Besides erosion control, additional benefits are an increase of water-holding capacity and reduction in bulk density. Currently, the above no-till farm experiment has lasted for 40 years and continues to report benefits to soil health and sustainable production (Reicosky and Crovetto 2014 <sup>[[#fn:r1510|1510]]</sup> ). The influence of this iconic farm has resulted in the adoption of soil conservation practices – and especially no-till – in dryland areas of the Mediterranean climate region of central Chile (Martínez et al. 2011 <sup>[[#fn:r1511|1511]]</sup> ). Currently, it has been estimated that the area under no-till farming in Chile varies between 0.13 and 0.2 Mha (Acevedo and Silva 2003 <sup>[[#fn:r1512|1512]]</sup> ).

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==== 3.7.1.3 Combating wind erosion and deflation in Turkey: The greening desert of Karapınar ====

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In Turkey, the amount of sediment recently released through erosion into seas was estimated to be 168 Mt yr <sup>-1</sup> , which is considerably lower than the 500 Mt yr <sup>–1</sup> that was estimated to be lost in the 1970s. The decrease in erosion rates is attributed to an increase in spatial extent of forests, rehabilitation of degraded forests, erosion control, prevention of overgrazing, and improvement in irrigation technologies. Soil conservation measures conducted in the Karapınar district, Turkey, exemplify these activities. The district is characterised by a semi-arid climate and annual average precipitation of 250–300 mm (Türkeş 2003 <sup>[[#fn:r1513|1513]]</sup> ; Türkeş and Tatlı 2011 <sup>[[#fn:r1514|1514]]</sup> ). In areas where vegetation was overgrazed or inappropriately tilled, the surface soil horizon was removed through erosion processes resulting in the creation of large drifting dunes that threatened settlements around Karapınar (Groneman 1968 <sup>[[#fn:r1515|1515]]</sup> ). Such dune movement had begun to affect the Karapınar settlement in 1956 (Kantarcı et al. 2011 <sup>[[#fn:r1516|1516]]</sup> ). Consequently, by the early 1960s, Karapınar town and nearby villages were confronted with the danger of abandonment due to out-migration in the early 1960s (Figure 3.11(1)). The reasons for increasing wind erosion in the Karapınar district can be summarised as follows: sandy material was mobilised following drying of the lake; hot and semi-arid climate conditions; overgrazing and use of pasture plants for fuel; excessive tillage; and strong prevailing winds.

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'''Figure 3.11a'''

<span id="a-general-view-of-a-nearby-village-of-karapınar-town-in-the-early-1960s-çarkaci-1999."></span>
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'''(1) A general view of a nearby village of Karapınar town in the early 1960s (Çarkaci 1999).'''
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[[File:94b8ddda39bc1f5c6cec209097079501 Figure-3.11a.png]]

(1) A general view of a nearby village of Karapınar town in the early 1960s (Çarkaci 1999) <sup>[[#fn:r1802|1802]]</sup> .

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<span id="figure-3.11b"></span>
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'''Figure 3.11b'''

<span id="a-view-of-the-karapınar-wind-erosion-area-in-2013-photo-murat-türkeş-17-june-2019."></span>
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'''(2)A view of the Karapınar wind erosion area in 2013 (Photo: Murat Türkeş, 17 June 2019).'''
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[[File:332259ecd3c1f439336fa3143309524a Figure-3.11b-1024x683.jpg]]

(2)A view of the Karapınar wind erosion area in 2013 (Photo: Murat Türkeş <sup>[[#fn:r1803|1803]]</sup> , 17 June 2019).

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<span id="figure-3.11c"></span>
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'''Figure 3.11c'''

<span id="construction-of-cane-screens-in-the-early-1960s-in-order-to-decrease-wind-speed-and-prevent-movement-of-the-sand-accumulations-and-dunes-this-was-one-of-the-physical-measures-during-the-prevention-and-mitigation-period-çarkaci-1999."></span>
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'''(3) Construction of cane screens in the early 1960s in order to decrease wind speed and prevent movement of the sand accumulations and dunes; this was one of the physical measures during the prevention and mitigation period (Çarkaci 1999).'''

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[[File:ef030280cb1db9bd660d1c4f6d826f54 Figure-3.11c.png]]

(3) Construction of cane screens in the early 1960s in order to decrease wind speed and prevent movement of the sand accumulations and dunes; this was one of the physical measures during the prevention and mitigation period (Çarkaci 1999 <sup>[[#fn:r1804|1804]]</sup> ).

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<span id="figure-3.11d"></span>
<!-- START IMG -->
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'''Figure 3.11d'''

<span id="a-view-of-mixed-vegetation-which-now-covers-most-of-the-karapınar-wind-erosion-area-in-2013-the-main-tree-species-of-which-were-selected-for-afforestation-with-respect-to-their-resistance-to-the-arid-continental-climate-conditions-along-with-a-warmhot-temperature-regime-over-the-district-photo-murat-türkeş-17-june-2013."></span>
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'''(4) A view of mixed vegetation, which now covers most of the Karapınar wind erosion area in 2013, the main tree species of which were selected for afforestation with respect to their resistance to the arid continental climate conditions along with a warm/hot temperature regime over the district (Photo: Murat Türkeş, 17 June 2013).'''
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[[File:4bca06773595a7299c60fb68e7be04f5 Figure-3.11d.png]]

(4) A view of mixed vegetation, which now covers most of the Karapınar wind erosion area in 2013, the main tree species of which were selected for afforestation with respect to their resistance to the arid continental climate conditions along with a warm/hot temperature regime over the district (Photo: Murat Türkeş <sup>[[#fn:r1805|1805]]</sup> , 17 June 2013).

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Restoration and mitigation strategies were initiated in 1959, and today 4300 ha of land have been restored (Akay and Yildirim 2010 <sup>[[#fn:r1517|1517]]</sup> ) (Figure 3.11 (2)), using specific measures: (i) physical measures: construction of cane screens to decrease wind speed and prevent sand movement (Figure 3.11(3)); (ii) restoration of cover: increasing grass cover between screens using seeds collected from local pastures or the cultivation of rye ( ''Secale'' sp.) and wheat grass ( ''Agropyron elongatum'' ) that are known to grow in arid and hot conditions; and (iii) afforestation: saplings obtained from nursery gardens were planted and grown between these screens. Main tree species selected were oleaster ( ''Eleagnus'' sp.), acacia ( ''Robinia pseudeaccacia'' ), ash ( ''Fraxinus'' sp.), elm ( ''Ulmus'' sp.) and maple (Acer sp.) (Figure 3.11 (4)). Economic growth occurred after controlling erosion and new tree nurseries have been established with modern irrigation. Potential negative consequences through the excessive use of water can be mitigated through engagement with local stakeholders and transdisciplinary learning processes, as well as by restoring the traditional land uses in the semi-arid Konya closed basin (Akça et al. 2016 <sup>[[#fn:r1518|1518]]</sup> ).

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==== 3.7.1.4 Soil erosion in Central Asia under changing climate ====

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Soil erosion is widely acknowledged to be a major form of degradation of Central Asian drylands, affecting a considerable share of croplands and rangelands. However, up-to-date information on the actual extent of eroded soils at the regional or country level is not available. The estimates compiled by Pender et al. (2009), based on the Central Asian Countries Initiative for Land Management (CACILM), indicate that about 0.8 Mha of the irrigated croplands were subject to high degree of soil erosion in Uzbekistan. In Turkmenistan, soil erosion was indicated to be occurring in about 0.7 Mha of irrigated land. In Kyrgyzstan, out of 1 Mha of irrigated land in the foothill zones, 0.76 Mha were subject to soil erosion by water, leading to losses in crop yields of 20–60% in these eroded soils. About 0.65 Mha of arable land were prone to soil erosion by wind (Mavlyanova et al. 2017 <sup>[[#fn:r1519|1519]]</sup> ). Soil erosion is widespread in rainfed and irrigated areas in Kazakhstan (Saparov 2014). About 5 Mha of rainfed croplands were subject to high levels of soil erosion (Pender et al. 2009 <sup>[[#fn:r1520|1520]]</sup> ). Soil erosion by water was indicated to be a major concern in sloping areas in Tajikistan (Pender et al. 2009 <sup>[[#fn:r1521|1521]]</sup> ).

The major causes of soil erosion in Central Asia are related to human factors, primarily excessive water use in irrigated areas (Gupta et al. 2009 <sup>[[#fn:r1522|1522]]</sup> ), deep ploughing and lack of maintenance of vegetative cover in rainfed areas (Suleimenov et al. 2014 <sup>[[#fn:r1523|1523]]</sup> ), and overgrazing in rangelands (Mirzabaev et al. 2016 <sup>[[#fn:r1524|1524]]</sup> ). Lack of good maintenance of watering infrastructure for migratory livestock grazing, and fragmentation of livestock herds led to overgrazing near villages, increasing the soil erosion by wind (Alimaev et al. 2008 <sup>[[#fn:r1526|1526]]</sup> ). Overgrazing in the rangeland areas of the region (e.g., particularly in Kyzylkum) contributes to dust storms, coming primarily from the Ustyurt Plateau, desertified areas of Amudarya and Syrdarya rivers’ deltas, the dried seabed of the Aral Sea (now called Aralkum), and the Caspian Sea (Issanova and Abuduwaili 2017 <sup>[[#fn:r1527|1527]]</sup> ; Xi and Sokolik 2015). Xi and Sokolik (2015) estimated that total dust emissions in Central Asia were 255.6 Mt in 2001, representing 10–17% of the global total.

Central Asia is one of the regions highly exposed to climate change, with warming levels projected to be higher than the global mean (Hoegh-Guldberg et al. 2018 <sup>[[#fn:r1528|1528]]</sup> ), leading to more heat extremes (Reyer et al. 2017 <sup>[[#fn:r1529|1529]]</sup> ). There is no clear trend in precipitation extremes, with some potential for moderate rise in occurrence of droughts. The diminution of glaciers is projected to continue in the Pamir and Tian Shan mountain ranges, a major source of surface waters along with seasonal snowmelt. Glacier melting will increase the hazards from moraine-dammed glacial lakes and spring floods (Reyer et al. 2017 <sup>[[#fn:r1530|1530]]</sup> ). Increased intensity of spring floods creates favourable conditions for higher soil erosion by water, especially in the sloping areas in Kyrgyzstan and Tajikistan. The continuation of some of the current unsustainable cropland and rangeland management practices may lead to elevated rates of soil erosion, particularly in those parts of the region where climate change projections point to increases in floods (Kyrgyzstan, Tajikistan) or increases in droughts (Turkmenistan, Uzbekistan) (Hijioka et al. 2014 <sup>[[#fn:r1531|1531]]</sup> ). Increasing water use to compensate for higher evapotranspiration due to rising temperatures and heat waves could increase soil erosion by water in the irrigated zones, especially in sloping areas and crop fields with uneven land levelling (Bekchanov et al. 2010 <sup>[[#fn:r1532|1532]]</sup> ). The desiccation of the Aral Sea resulted in a hotter and drier regional microclimate, adding to the growing wind erosion in adjacent deltaic areas and deserts (Kust 1999 <sup>[[#fn:r1533|1533]]</sup> ).

There are numerous sustainable land and water management practices available in the region for reducing soil erosion (Abdullaev et al. 2007 <sup>[[#fn:r1534|1534]]</sup> ; Gupta et al. 2009 <sup>[[#fn:r1535|1535]]</sup> ; Kust et al. 2014 <sup>[[#fn:r1536|1536]]</sup> ; Nurbekov et al. 2016 <sup>[[#fn:r1537|1537]]</sup> ). These include: improved land levelling and more efficient irrigation methods such as drip, sprinkler and alternate furrow irrigation (Gupta et al. 2009 <sup>[[#fn:r1538|1538]]</sup> ); conservation agriculture practices, including no-till methods and maintenance of crop residues as mulch in the rainfed and irrigated areas (Kienzler et al. 2012 <sup>[[#fn:r1539|1539]]</sup> ; Pulatov et al. 2012 <sup>[[#fn:r1540|1540]]</sup> ); rotational grazing; institutional arrangements for pooling livestock for long-distance mobile grazing; reconstruction of watering infrastructure along the livestock migratory routes (Han et al. 2016; Mirzabaev et al. 2016 <sup>[[#fn:r1541|1541]]</sup> ); afforesting degraded marginal lands (Djanibekov and Khamzina 2016 <sup>[[#fn:r1543|1543]]</sup> ; Khamzina et al. 2009 <sup>[[#fn:r1545|1545]]</sup> ; Khamzina et al. 2016 <sup>[[#fn:r1546|1546]]</sup> ); integrated water resource management (Dukhovny et al. 2013 <sup>[[#fn:r1547|1547]]</sup> ; Kazbekov et al. 2009 <sup>[[#fn:r1548|1548]]</sup> ); and planting salt – and drought-tolerant halophytic plants as windbreaks in sandy rangelands (Akinshina et al. 2016 <sup>[[#fn:r1549|1549]]</sup> ; Qadir et al. 2009 <sup>[[#fn:r1550|1550]]</sup> ; Toderich et al. 2009 <sup>[[#fn:r1551|1551]]</sup> ; Toderich et al. 2008 <sup>[[#fn:r1552|1552]]</sup> ), and potentially the dried seabed of the former Aral Sea (Breckle 2013 <sup>[[#fn:r1553|1553]]</sup> ). The adoption of enabling policies, such as those discussed in Section 3.6.3, can facilitate the adoption of these sustainable land and water management practices in Central Asia ( ''high confidence'' ) (Aw-Hassan et al. 2016 <sup>[[#fn:r1554|1554]]</sup> ; Bekchanov et al. 2016 <sup>[[#fn:r1555|1555]]</sup> ; Bobojonov et al. 2013 <sup>[[#fn:r1556|1556]]</sup> ; Djanibekov et al. 2016 <sup>[[#fn:r1557|1557]]</sup> ; Hamidov et al. 2016 <sup>[[#fn:r1559|1559]]</sup> ; Mirzabaev et al. 2016 <sup>[[#fn:r1560|1560]]</sup> ).

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