Editing IPCC:AR6/SRCCL/Chapter-6 (section)

==== 6.3.3.1 Integrated response options based on land management ====

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In this section, the impacts on desertification of integrated response options based on land management are assessed.

''Integrated response options based on land management in agriculture''

Burney et al. (2010) estimated that an additional global cropland area of 11.11–15.14 Mkm <sup>2</sup> would have been needed if productivity had not increased between 1961 and 2000. Given that agricultural expansion is a main driver of desertification (FAO and ITPS 2015 <sup>[[#fn:r492|492]]</sup> ), increased food productivity could have prevented up to 11.11–15.14 Mkm <sup>2</sup> from exploitation and desertification (Table 6.10).

Improved cropland, livestock and grazing land management are strategic options aimed at prevention of desertification, and may include crop and animal selection, optimised stocking rates, changed tillage and/or cover crops, to land-use shifting from cropland to rangeland, in general targeting increases in ground cover by vegetation, and protection against wind erosion (Schwilch et al. 2014 <sup>[[#fn:r493|493]]</sup> ; Bestelmeyer et al. 2015 <sup>[[#fn:r494|494]]</sup> ). Considering the widespread distribution of deserts and desertified lands globally, more than 10 Mkm <sup>2</sup> could benefit from improved management techniques.

Agroforestry can help stabilise soils to prevent desertification (Section 6.3.2.1), so given that there is around 10 Mkm <sup>2</sup> of land with more than 10% tree cover (Garrity 2012 <sup>[[#fn:r495|495]]</sup> ), agroforestry could benefit up to 10 Mkm <sup>2</sup> of land.

Agricultural diversification to prevent desertification may include the use of crops with manures, legumes, fodder legumes and cover crops combined with conservation tillage systems (Schwilch et al. 2014 <sup>[[#fn:r496|496]]</sup> ). These practices can be considered to be part of improved crop management options (see above) and aim at increasing ground coverage by vegetation and controlling wind erosion losses.

Since shifting from grassland to the annual cultivation of crops increases erosion and soil loss, there are significant benefits for desertification control, by stabilising soils in arid areas (Chapter 3). Cropland expansion during 1985 to 2005 was 359,000 km2, or 17,400 Mkm <sup>2</sup> yr <sup>–1</sup> (Foley et al. 2011). Not all of this expansion will be from grasslands or in desertified areas, but this value sets the maximum contribution of prevention of conversion of grasslands to croplands, a small global benefit for desertification control (Table 6.10).

Integrated water management strategies such as water-use efficiency and irrigation, improve soil health through increase in soil organic matter content, thereby delivering benefits for prevention or reversal of desertification (Baumhardt et al. 2015 <sup>[[#fn:r1259|1259]]</sup> ; Datta et al. 2000 <sup>[[#fn:r497|497]]</sup> ; Evans and Sadler 2008 <sup>[[#fn:r498|498]]</sup> ; He et al. 2015 <sup>[[#fn:r499|499]]</sup> ) (Chapter 3). Climate change will amplify existing stress on water availability and on agricultural systems, particularly in semi-arid environments (IPCC AR5 2014 <sup>[[#fn:r500|500]]</sup> ) (Chapter 3). In 2011, semi-arid ecosystems in the southern hemisphere contributed 51% of the global net carbon sink (Poulter et al. 2014 <sup>[[#fn:r501|501]]</sup> ). These results suggest that arid ecosystems could be an important global carbon sink, depending on soil water availability.

Table 6.29 summarises the impacts on desertification of agricultural options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.29'''

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'''Effects on desertification of response options in agriculture.'''
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''Integrated response options based on land management in forestry''

Forests are important to help to stabilise land and regulate water and microclimate (Locatelli et al. 2015b <sup>[[#fn:r1260|1260]]</sup> ). Based on the extent of dry forest at risk of desertification (Núñez et al. 2010 <sup>[[#fn:r1261|1261]]</sup> ; Bastin et al. 2017 <sup>[[#fn:r1262|1262]]</sup> ), the estimated global potential effect for avoided desertification is large for both forest management and for reduced deforestation and forest degradation when cumulated for at least 20 years (Table 6.30). The uncertainty of these global estimates is high. More robust qualitative and some quantitative estimates are available at regional level. For example, it has been simulated that human activity (i.e., land management) contributed to 26% of the total land reverted from desertification in Northern China between 1981 and 2010 (Xu et al. 2018 <sup>[[#fn:r1263|1263]]</sup> ). In Thailand, it was found that the desertification risk is reduced when the land use is changed from bare lands to agricultural lands and forests, and from non-forests to forests; conversely, the desertification risk increases when converting forests and denuded forests to bare lands (Wijitkosum 2016 <sup>[[#fn:r1264|1264]]</sup> ).

Afforestation, reforestation and forest restoration are land management response options that are used to prevent desertification. Forests tend to maintain water and soil quality by reducing runoff and trapping sediments and nutrients (Medugu et al. 2010 <sup>[[#fn:r505|505]]</sup> ; Salvati et al. 2014 <sup>[[#fn:r506|506]]</sup> ), but planting of non-native species in semi-arid regions can deplete soil water resources if they have high evapotranspiration rates (Zeng et al. 2016 <sup>[[#fn:r507|507]]</sup> ; Yang et al. 2014 <sup>[[#fn:r508|508]]</sup> ). Afforestation and reforestation programmes can be deployed over large areas of the Earth, so can create synergies in areas prone to desertification. Global estimates of land potentially available for afforestation are up to 25.8 Mkm <sup>2</sup> by the end of the century, depending on a variety of assumptions on socio- economic developments and climate policies (Griscom et al. 2017; Kreidenweis et al. 2016 <sup>[[#fn:r509|509]]</sup> ; Popp et al. 2017 <sup>[[#fn:r510|510]]</sup> ). The higher end of this range is achieved under the assumption of a globally uniform reward for carbon uptake in the terrestrial biosphere, and it is halved by considering tropical and subtropical areas only to minimise albedo feedbacks (Kreidenweis et al. 2016 <sup>[[#fn:r511|511]]</sup> ). When safeguards are introduced (e.g., excluding existing cropland for food security, boreal areas, etc.), the area available declines to about 6.8 Mkm <sup>2</sup> (95% confidence interval of 2.3 and 11.25 Mkm <sup>2</sup> ), of which about 4.72 Mkm <sup>2</sup> is in the tropics and 2.06 Mkm <sup>2</sup> is in temperate regions (Griscom et al. 2017 <sup>[[#fn:r512|512]]</sup> ) (Table 6.30).

Table 6.30 summarises the impacts on desertification of forestry options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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<span id="table-6.30"></span>
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'''Table 6.30'''

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'''Effects on desertification of response options in forests.'''
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[[File:e5cac25d7ea497673c6cf0b1c27dff1c table-6.30.png]]

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Integrated response options based on land management of soils

With more than 2.7 billion people affected globally by desertification (IPBES 2018) <sup>[[#fn:r513|513]]</sup> , practices to increase soil organic carbon content are proposed as actions to address desertification, and could be applied to an estimated 11.37 Mkm <sup>2</sup> of desertified soils (Lal 2001 <sup>[[#fn:r514|514]]</sup> ) (Table 6.31).

Control of soil erosion could have large benefits for desertification control. Using figures from FAO et al. (2015) <sup>[[#fn:r515|515]]</sup> , IPBES (2018) <sup>[[#fn:r1270|1270]]</sup> estimated that land losses due to erosion to 2050 are equivalent to 1.5 Mkm2 of land from crop production, or 45,000 km <sup>2</sup> yr <sup>–1</sup> (Foley et al. 2011) so soil erosion control could benefit up to 1.50 Mkm2 of land in the coming decades. Lal (2001) <sup>[[#fn:r517|517]]</sup> estimated that desertification control (using soil erosion control as one intervention) could benefit 11.37 Mkm <sup>2</sup> of desertified land globally (Table 6.10).

Oldeman et al. (1991) estimated that the global extent soil affected by salinisation is 0.77 Mkm <sup>2</sup> yr <sup>–1</sup> ,which sets the upper limit on the area that could benefit from measures to address soil salinisation (Table 6.31).

In degraded arid grasslands, shrublands and rangelands, desertification can be reversed by alleviation of soil compaction through installation of enclosures and removal of domestic livestock (Allington et al. 2010 <sup>[[#fn:r518|518]]</sup> ), but there are no global estimates of potential (Table 6.31).

Biochar could potentially deliver benefits in efforts to address desertification though improving water-holding capacity (Woolf et al. 2010 <sup>[[#fn:r519|519]]</sup> ; Sohi 2012 <sup>[[#fn:r520|520]]</sup> ), but the global effect is not quantified.

Table 6.31 summarises the impacts on desertification of soil-based options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.31'''

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'''Effects on desertification of land management of soils.'''
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Integrated response options based on land management across all/other ecosystems

For fire management, Arora and Melton (2018) <sup>[[#fn:r521|521]]</sup> estimated, using models and GFED4.1s0 data, that burned area over the 1997–2014 period was 4.834–4.855 Mkm <sup>2</sup> yr <sup>–1</sup> . Randerson et al. (2012) <sup>[[#fn:r522|522]]</sup> estimated small fires increased total burned area globally by 35% from 3.45 to 4.64 Mkm <sup>2</sup> yr <sup>–1</sup> during the period 2001–2010. Tansey et al. (2004) <sup>[[#fn:r523|523]]</sup> estimated that over 3.5 Mkm <sup>2</sup> yr <sup>–1</sup> of burned areas were detected in the year 2000 (Table 6.32).

Although slope and slope aspect are predictive factors of desertification occurrence, the factors with the greatest influence are land cover factors, such as normalised difference vegetation index (NDVI) and rangeland classes (Djeddaoui et al. 2017 <sup>[[#fn:r524|524]]</sup> ). Therefore, prevention of landslides and natural hazards exert indirect influence on the occurrence of desertification.

The global extent of chemical soil degradation (salinisation, pollution and acidification) is about 1.03 Mkm <sup>2</sup> yr <sup>–1</sup> (Oldeman et al. 1991 <sup>[[#fn:r525|525]]</sup> ), giving the maximum extent of land that could benefit from the management of pollution and acidification.

There are no global data on the impacts of management of invasive species/encroachment on desertification, though the impact is presumed to be positive. There are no studies examining the potential role of restoration and avoided conversion of coastal wetlands on desertification.

There are no impacts of peatland restoration for prevention of desertification, as peatlands occur in wet areas and deserts in arid areas, so they are not connected.

For management of pollution, including acidification, Oldeman et al. (1991) estimated the global extent of chemical soil degradation, with 0.77 Mkm <sup>2</sup> yr <sup>–1</sup> affected by salinisation, 0.21 Mkm <sup>2</sup> yr <sup>–1</sup> affected by pollution, and 0.06 Mkm <sup>2</sup> yr <sup>–1</sup> affected by acidification (total: 1.03 Mkm <sup>2</sup> yr <sup>–1</sup> ), so this is the area that could potentially benefit from pollution management measures.

Biodiversity conservation measures can interact with desertification, but the literature contains no global estimates of potential.

Table 6.32 summarises the impacts on desertification of options on all/other ecosystems, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.32'''

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'''Effects on desertification of response options on all/other ecosystems.'''
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''Integrated response options based on land management specifically for carbon dioxide removal (CDR)''

While spreading of crushed minerals onto land as part of enhanced weathering may provide soil/plant nutrients in nutrient-depleted soils (Beerling et al. 2018), there is no literature reporting on the potential global impacts of this in addressing desertification.

Large-scale production of bioenergy can require significant amounts of land (Smith et al. 2016a <sup>[[#fn:r527|527]]</sup> ; Clarke et al. 2014 <sup>[[#fn:r528|528]]</sup> ; Popp et al. 2017 <sup>[[#fn:r529|529]]</sup> ), with as much as 15 Mkm <sup>2</sup> in 2100 in 2°C scenarios (Popp et al. 2017 <sup>[[#fn:r530|530]]</sup> ), increasing pressures for desertification (Table 6.33).

Table 6.33 summarises the impacts on desertification of options specifically for CDR, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.33'''

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