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

=== 6.1.3 Challenges and response options in current and historical interventions ===

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Land-based systems are exposed to multiple overlapping challenges, including climate change (adaptation and mitigation), desertification (Chapter 3), land degradation (Chapter 4) and food insecurity (Chapter 5), as well as loss of biodiversity, groundwater stress (from over-abstraction) and water quality. The spatial distribution of these individual land-based challenges is shown in Figure 6.2, based on recent studies and using the following indicators:

* Desertification attributed to land use is estimated from vegetation remote sensing (Figure 3.7c), mean annual change in NDVImax &lt;–0.001 (between 1982 and 2015) in dryland areas (Aridity Index &gt;0.65), noting, however, that desertification has multiple causes (Chapter 3).
* Land degradation (Chapter 4) is based on a soil erosion (Borrelli et al. 2017 <sup>[[#fn:r18|18]]</sup> ) proxy (annual erosion rate of 3 t ha <sup>–1</sup> or above).
* The climate change challenge for adaptation is based on a dissimilarity index of monthly means of temperature and precipitation between current and end-of-century scenarios (dissimilarity index equal to 0.7 or above; Netzel and Stepinski 2018 <sup>[[#fn:r19|19]]</sup> ), noting, however, that rapid warming could occur in all land regions (Chapter 2).
* The food security challenge is estimated as the prevalence of chronic undernourishment (higher or equal to 5%) by country in 2015 (FAO 2017a <sup>[[#fn:r20|20]]</sup> ), noting, however, that food security has several dimensions (Chapter 5).
* The biodiversity challenge uses threatened terrestrial biodiversity hotspots (areas where exceptional concentrations of endemic species are undergoing exceptional loss of habitat, (Mittermeier et al. 2011 <sup>[[#fn:r21|21]]</sup> ), noting, however, that biodiversity concerns more than just threatened endemic species.
* The groundwater stress challenge is estimated as groundwater abstraction over recharge ratios above one (Gassert et al. 2014 <sup>[[#fn:r22|22]]</sup> ) in agricultural areas (croplands and villages).
* The water quality challenge is estimated as critical loads (higher or equal to 1000 kg N km <sup>–2</sup> or 50 kg P km <sup>–2</sup> ) of nitrogen (N) and phosphorus (P) (Xie and Ringler 2017 <sup>[[#fn:r23|23]]</sup> ).

Overlapping land-based challenges affect all land-use categories: croplands, rangelands, semi-natural forests, villages, dense settlements, wild forests and sparse trees and barren lands. These land-use categories can be defined as anthropogenic biomes, or anthromes, and their global distribution was mapped by Ellis and Ramankutty (2008) <sup>[[#fn:r24|24]]</sup> (Figure 6.2).

The majority of the global population is concentrated in dense settlements and villages, accounting for less than 7% of the global ice-free land area, while croplands and rangelands use 39% of land. The remainder of the ice-free land area (more than half) is used by semi-natural forests, by wild forests, sparse trees and barren lands (Table 6.1).

Land-use types (or anthromes) are exposed to multiple overlapping challenges. Climate change could induce rapid warming in all land areas (Chapter 2). In close to 70% of the ice-free land area, the climate change adaptation challenge could be reinforced by a strong dissimilarity between end-of-century and current temperature and precipitation seasonal cycles (Netzel and Stepinski 2018 <sup>[[#fn:r25|25]]</sup> ). Chronic undernourishment (a component of food insecurity) is concentrated in 20% of global ice-free land area. Severe soil erosion (a proxy of land degradation) and desertification from land use affect 13% and 3% of ice-free land area, respectively. Both groundwater stress and severe water-quality decline (12% and 10% of ice-free land area, respectively) contribute to the water challenge. Threatened biodiversity hot-spots (15% of ice-free land area) are significant for the biodiversity challenge (Table 6.1).

Since land-based challenges overlap, part of the ice-free land area is exposed to combinations of two or more challenges. For instance, land degradation (severe soil erosion) or desertification from land use and food insecurity (chronic undernourishment) are combined with a strong climate change adaptation challenge (dissimilarity in seasonal cycles) in 4.5% of the ice-free land area (Figure 6.3).

The global distribution of land area by the number of overlapping land challenges (Figure 6.4) shows: the least exposure to land challenges in barren lands; less frequent exposure to two or more challenges in wild forests than in semi-natural forests; more frequent exposure to two or more challenges in agricultural anthromes (croplands and rangelands) and dense settlements than in forests; most frequent exposure to three or more challenges in villages compared to other land-use types. Therefore, land-use types intensively used by humans are, on average, exposed to a larger number of challenges than land- use types (or anthromes) least exposed to human use.

Case studies located in different world regions are presented for each anthrome, in order to provide historical context on the interlinkages between multiple challenges and responses (Box 6.1). Taken together, these case studies illustrate the large contrast across anthromes in land-based interventions, and show the way these interventions respond to combinations of challenges.

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<span id="figure-6.2"></span>
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'''Figure 6.2'''

<span id="global-distributions-of-land-use-types-and-individual-land-based-challenges.a-land-use-types-or-anthromes-after-ellis-and-ramankutty-2008-b-climate-change-adaptation-challenge-estimated-from-the-dissimilarity-between-current-and-end-of-century-climate-scenarios-netzel-and-stepinski-2018-c-desertification-challenge-after-chapter-3-figure-3.7c-d-land-degradation-challenge-estimated-from-a-soil-erosion-proxy"></span>
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'''Global distributions of land-use types and individual land-based challenges.(a) Land-use types (or anthromes, after Ellis and Ramankutty 2008); (b) Climate change adaptation challenge (estimated from the dissimilarity between current and end-of-century climate scenarios, Netzel and Stepinski 2018); (c) Desertification challenge (after Chapter 3, Figure 3.7c); (d) Land degradation challenge (estimated from a soil erosion proxy, […]'''
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[[File:591597f7860c9c91aaeebf45efdb6834 Figure-6.2-848x1024.jpg]]

Global distributions of land-use types and individual land-based challenges.(a) Land-use types (or anthromes, after Ellis and Ramankutty 2008 <sup>[[#fn:r1229|1229]]</sup> ); (b) Climate change adaptation challenge (estimated from the dissimilarity between current and end-of-century climate scenarios, Netzel and Stepinski 2018 <sup>[[#fn:r1230|1230]]</sup> ); (c) Desertification challenge (after Chapter 3, Figure 3.7c); (d) Land degradation challenge (estimated from a soil erosion proxy, one indicator of land degradation; Borrelli et al. 2017 <sup>[[#fn:r1231|1231]]</sup> ); (e) Food security challenge (estimated from chronic undernourishment, a component of food security, FAO 2017a <sup>[[#fn:r1232|1232]]</sup> ); (f) biodiversity challenge (estimated from threatened biodiversity hotspots, a component of biodiversity, Mittermeier et al. 2011 <sup>[[#fn:r1233|1233]]</sup> ]); (g) Groundwater stress challenge (estimated from water over-abstraction, Gassert et al. 2014 <sup>[[#fn:r1234|1234]]</sup> ); (h) Water quality challenge (estimated from critical nitrogen and phosphorus loads of water systems, Xie and Ringler 2017 <sup>[[#fn:r1235|1235]]</sup> ).

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<span id="table-6.1"></span>
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'''Table 6.1'''

<span id="global-area-of-land-use-types-or-anthromes-and-current-percentage-area-exposure-to-individual-overlapping-land-based-challenges."></span>
'''Global area of land-use types (or anthromes) and current percentage area exposure to individual (overlapping) land-based challenges.'''

See Figure 6.2 and text for further details on criteria for individual challenges.

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{| class="wikitable"
|-

Land-use type (anthromea)

Anthrome area

Climate

change adaptation (dissimilarity index proxy)b

Land degradation (soil erosion proxy)c

Desertifica- tion (ascribed to land use)d

Food security (chronic undernourish- ment)e

Biodiversity (threatened hotspot)f

Groundwater stress (over abstraction)g

Water quality (critical N-P loads)h

|-
|

% of ice-free land areai

|

% anthrome area exposed to an individual challenge

|
|-

Dense settlement

1

76

20

3

30

32

–

30

|-

Village

5

70

49

3

78

28

77

59

|-

Cropland

13

68

21

7

28

27

65

20

|-

Rangeland

26

46

14

7

43

21

–

10

|-

Semi-natural forests

14

91

17

0.7

–

21

–

7

|-

Wild forests and sparse trees

17

98

4

0.5

–

2

–

0.3

|-

Barren

19

53

6

0.9

2

4

–

0.4

|-

\*Organic soils

4

95

10

2

9

13

–

6

|-

\*Coastal wetlands

0.6

74

11

2

24

33

–

26

|-

All anthromes

100

69

13

3.2

20

15

12

10

|}
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a Ellis and Ramankutty (2008) <sup>[[#fn:r1236|1236]]</sup> ; b Borrelli et al. 2017 <sup>[[#fn:r1237|1237]]</sup> ; c Netzel and Stepinski 2018 <sup>[[#fn:r1238|1238]]</sup> ; d from Figure 3.7c in Chapter 3; e FAO 2017a <sup>[[#fn:r1239|1239]]</sup> ; f Mittermeier et al. 2011 <sup>[[#fn:r1240|1240]]</sup> ; g Gassert et al. 2014 <sup>[[#fn:r1241|1241]]</sup> ; h Xie and Ringler 2017 <sup>[[#fn:r1242|1242]]</sup> ; i the global ice-free land area is estimated at 134 Mkm <sup>2</sup> .

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<span id="figure-6.3"></span>
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'''Figure 6.3'''

<span id="example-of-overlap-between-land-challenges.-a-overlap-between-the-desertification-from-land-use-challenge-and-the-climate-change-adaptation-strong-dissimilarity-in-seasonal-cycles-challenge.-b-overlap-between-the-land-degradation-soil-erosion-proxy-challenge-and-the-climate-change-adaptation-challenge.-c-overlap-between-the-desertification-or-land-degradation-challenges-and-the-food-insecurity"></span>
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'''Example of overlap between land challenges. (a) Overlap between the desertification (from land use) challenge and the climate change adaptation (strong dissimilarity in seasonal cycles) challenge. (b) Overlap between the land degradation (soil erosion proxy) challenge and the climate change adaptation challenge. (c) Overlap between the desertification or land degradation challenges and the food insecurity […]'''
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[[File:71328a6fe18b72e63dac3c15956c9688 Figure-6.3-1024x602.jpg]]

Example of overlap between land challenges. (a) Overlap between the desertification (from land use) challenge and the climate change adaptation (strong dissimilarity in seasonal cycles) challenge. (b) Overlap between the land degradation (soil erosion proxy) challenge and the climate change adaptation challenge. (c) Overlap between the desertification or land degradation challenges and the food insecurity (chronic undernourishment) challenge. (d) Overlap between challenges shown in C and the climate change adaptation challenge. For challenges definitions, see text; references as in Figure 6.2.

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<span id="figure-6.4"></span>
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'''Figure 6.4'''

<span id="percentage-distribution-of-land-use-type-or-anthrome-area-by-number-of-overlapping-land-challenges-for-the-villages-dense-settlements-croplands-rangelands-semi-natural-forests-wild-forests-and-sparse-trees-and-barren-land-use-types.-values-in-brackets-show-the-mean-number-of-land-challenges-per-land-use-type.-land-challenges-include-desertification-from-land-use-land-degradation-soil"></span>
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'''Percentage distribution of land-use type (or anthrome) area by number of overlapping land challenges for the villages, dense settlements, croplands, rangelands, semi-natural forests, wild forests and sparse trees and barren land-use types. Values in brackets show the mean number of land challenges per land-use type. Land challenges include desertification (from land use), land degradation (soil […]'''
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[[File:6bb25db1eff5dbdf64fb2f65d11451ed Figure-6.4-1024x599.jpg]]

Percentage distribution of land-use type (or anthrome) area by number of overlapping land challenges for the villages, dense settlements, croplands, rangelands, semi-natural forests, wild forests and sparse trees and barren land-use types. Values in brackets show the mean number of land challenges per land-use type. Land challenges include desertification (from land use), land degradation (soil erosion proxy), climate change adaptation (seasonal dissimilarity proxy), food security (chronic undernourishment), biodiversity (threatened hot spots), groundwater stress (over abstraction) and water quality (critical nitrogen and phosphorus loads).

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<div id="section-6-1-3-challenges-and-response-options-in-current-and-historical-interventions-block-6" class="box"></div>

<span id="box-6.1-case-studies-by-anthrome-type-showing-historical-interlinkages-between-land-based-challenges-and-the-development-of-local-responses"></span>