Editing IPCC:AR6/WGII/Cross-Chapter-Paper-3 (section)

== CCP3.2 Observed Impacts of Climate Change Across Sectors and Regions ==

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<span id="ccp3.2.1-observed-impacts-on-natural-systems-in-arid-and-semiarid-areas"></span>
=== CCP3.2.1 Observed Impacts on Natural Systems in Arid and Semiarid Areas ===

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<div id="CCP3.2.1.1" class="h3-container"></div>

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==== CCP3.2.1.1 Temperature and Rainfall ====

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Significant warming has occurred across drylands globally ( [[#IPCC--2021|IPCC, 2021]] ). Surface warming (1920–2015) of 1.2 ° C–1.3 ° C in global drylands has exceeded the 0.8 ° C–1.0 ° C warming over humid lands ( [[#Huang--2017|Huang et al., 2017]] ). As measured by the AI, this has expanded the area of drylands by ~4% from 1948–2004 ( [[#Ji--2015|Ji et al., 2015]] ; [[#Spinoni--2015|Spinoni et al., 2015]] ; [[#Huang--2016|Huang et al., 2016]] ). However, as mentioned in Figure CCP3.1, the AI has various limitations in assessing drylands expansion. Increases in potential evapotranspiration have exceeded increases in precipitation in the last half of the period 1901–2017 ( [[#Pan--2021|Pan et al., 2021]] ). Observations from the Sahel demonstrated that temperature seasonality changes differ from rainfall seasonality changes (Guichard et al., 2015), and there has been an increase in surface water and groundwater recharge in the Sahel since the 1980s, referred to as ‘the Sahel paradox’ ( [[#Favreau--2009|Favreau et al., 2009]] ; [[#Gardelle--2010|Gardelle et al., 2010]] ; [[#Descroix--2013|Descroix et al., 2013]] ; [[#Wendling--2019|Wendling et al., 2019]] ). Research from the USA suggests that historical soil moisture levels can contribute to such variability ( [[#Heisler-White--2009|Heisler-White et al., 2009]] ). Studies from the Middle East show rising temperatures and declining rainfall trends ( [[#ESCWA--2017|ESCWA, 2017]] ), with most decreasing aridity trends in north Sudan and most increasing aridity trends in eastern Arabia over the period 1948–2018 ( [[#Sahour--2020|Sahour et al., 2020]] ).

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<span id="ccp3.2.1.2-ecosystem-processes"></span>
==== CCP3.2.1.2 Ecosystem Processes ====

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Semiarid ecosystems have a disproportionately large role in the global carbon cycle, driving trends and interannual variability of the global carbon sink (Alstrom et al., 2015). These systems are highly sensitive to annual precipitation and temperature variations ( ''high confidence'' ) (Alstrom et al., 2015, Poulter et al., 2014). The positive trend in semiarid regions is consistent with widespread woody encroachment and increased vegetation greenness ( [[#Andela--2013|Andela et al., 2013]] ; [[#Piao--2019|Piao et al., 2019]] ; [[#Piao--2020|Piao et al., 2020]] ) driven by CO 2 fertilization and rainfall increases ( [[#Sitch--2015|Sitch et al., 2015]] ; [[#Piao--2020|Piao et al., 2020]] ), although some trends are complicated by irrigation practices ( [[#He--2019|He et al., 2019]] ). Increases in temperature and drought diminish this trend through reduced vegetation productivity and increased vegetation mortality ( [[#Brandt--2016|Brandt et al., 2016]] ; [[#Ma--2016|Ma et al., 2016]] ; [[#Fernández-Martínez--2019|Fernández-Martínez et al., 2019]] ; [[#Maurer--2020|Maurer et al., 2020]] ) with indications that this trend is declining or reversing in some locations ( [[#Yuan--2019|Yuan et al., 2019]] ; [[#Wang--2020|Wang et al., 2020]] ).

Changed climates have increased water constraints of vegetation growth most notably in the Mediterranean (Sections [[#CCP1.2.3.2|CCP1.2.3.2]] ; [[#CCP4.2.1|CCP4.2.1]] ) and West and Central Asia ( [[#Jiao--2021|Jiao et al., 2021]] ) ''.'' Climate change and elevated CO 2 have both increased and decreased vegetation sensitivity to rainfall throughout drylands, with the degree of variation shaped by region, land use and vegetation traits ( [[#Haverd--2017|Haverd et al., 2017]] ; [[#Abel--2021|Abel et al., 2021]] ). Mineral nitrogen production in drylands may become increasingly decoupled from consumption by plants over prolonged dry periods, and more extreme hydrological events can drive multiple changes to nutrient cycling ( [[#Manzoni--2019|Manzoni et al., 2019]] ). Soil biocrusts (composed of lichens, bryophytes and soil microorganisms), which contribute to dryland ecosystem function, including carbon uptake and soil stabilisation ( [[#Reed--2019|Reed et al., 2019]] ), are sensitive to warming and altered rainfall in a shift in biocrust communities of mosses and lichens in favour of early successional cyanobacteria-dominated biocrusts ( [[#Escolar--2012|Escolar et al., 2012]] ; [[#Reed--2012|Reed et al., 2012]] ), which can increase surface albedo ( [[#Rutherford--2017|Rutherford et al., 2017]] ).

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<span id="ccp3.2.1.3-vegetation-changes"></span>
==== CCP3.2.1.3 Vegetation Changes ====

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<span id="ccp3.2.1.4-woody-cover-increase"></span>
==== CCP3.2.1.4 Woody Cover Increase ====

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Dryland ecosystems have shown mixed trends of decreases and increases in vegetation and biodiversity, depending on the time period, geographic region and vegetation type assessed (see Table CCP3.1 for examples of observed environmental changes and impacts in drylands and the role of climate change and non-climatic factors in causing these changes).

Increases in shrub cover in arid deserts and shrublands have been recorded in the North American drylands ( [[#Caracciolo--2016|Caracciolo et al., 2016]] ; [[#Archer--2017|Archer et al., 2017]] ; [[#Chambers--2019|Chambers et al., 2019]] ), the Namib desert ( [[#Rohde--2019|Rohde et al., 2019]] ), the Karoo ( [[#Ward--2014|Ward et al., 2014]] ; [[#Masubelele--2015b|Masubelele et al., 2015b]] ), north and central Mexico ( [[#Pérez-Sánchez--2011|Pérez-Sánchez et al., 2011]] ; [[#Báez--2013|Báez et al., 2013]] ; [[#Castillón--2015|Castillón et al., 2015]] ; [[#Sosa--2019|Sosa et al., 2019]] ), large parts of the West African Sahel with some local exceptions ( [[#Brandt--2016|Brandt et al., 2016]] ) and Central Asia ( [[#Jia--2015|Jia et al., 2015]] ; [[#Li--2015|Li et al., 2015]] ; [[#Deng--2016|Deng et al., 2016]] ; [[#Jiao--2016|Jiao et al., 2016]] ; [[#Wang--2016|Wang et al., 2016]] ). Increasing woodiness in the Namib is consistent with an increase in rainfall extremes and westward expansion of convective rainfall ( [[#Haensler--2010|Haensler et al., 2010]] ; [[#Rohde--2019|Rohde et al., 2019]] ). Increasing rainfall and rising CO 2 concentrations (which improves water use efficiency) benefits some shrubs ( [[#Polley--1997|Polley et al., 1997]] ; [[#Morgan--2004|Morgan et al., 2004]] ; [[#Donohue--2013|Donohue et al., 2013]] ). Together with changes in land use ( [[#Hoffman--2018|Hoffman et al., 2018]] ), improved land management ( [[#Reij--2005|Reij et al., 2005]] ) and improved irrigation ( [[#He--2019|He et al., 2019]] ), this contributes to woody cover increases. Extensive woody encroachment has been recorded in savannas (measured between 1920–2015, over the past century) in Africa (2.4% woody cover increase per decade), Australia (1% increase per decade), and South America (8% increase per decade) ( [[#O’Connor--2014|O’Connor et al., 2014]] ; [[#Stevens--2016|Stevens et al., 2016]] ; [[#Skowno--2017|Skowno et al., 2017]] ; [[#Venter--2018|Venter et al., 2018]] ; [[#Zhang--2019|Zhang et al., 2019]] ). Following drought in the Sahel (1968–1973 and 1982–1984), a rainfall increase since the mid-1990s has been linked to increases of woody cover between 1992–2011/2012 ( [[#Brandt--2016|Brandt et al., 2016]] ; [[#Brandt--2017|Brandt et al., 2017]] ; [[#Brandt--2019|Brandt et al., 2019]] ). See SRCCL [[IPCC:Wg2:Chapter:Chapter-3#3.2.1|Section 3.2.1.1]] for an evaluation of the normalized difference vegetation index (NDVI) and remote sensing approaches used in these studies. Tree regeneration by farmers has also increased woody cover, particularly next to villages ( ''high confidence'' ) ( [[#Reij--2005|Reij et al., 2005]] ; [[#Reij--2016|Reij and Garrity, 2016]] ; [[#Brandt--2018|Brandt et al., 2018]] ). Otherwise, savanna encroachment has been attributed to combinations of increased rainfall ( [[#Venter--2018|Venter et al., 2018]] ; [[#Zhang--2019|Zhang et al., 2019]] ), warming ( [[#Venter--2018|Venter et al., 2018]] ) and CO 2 fertilization ( [[#Kgope--2010|Kgope et al., 2010]] ; [[#Bond--2012|Bond and Midgley, 2012]] ; [[#Buitenwerf--2012|Buitenwerf et al., 2012]] ; [[#Stevens--2016|Stevens et al., 2016]] ; [[#Quirk--2019|Quirk et al., 2019]] ) interacting with changing land use ( [[#Archer--2017|Archer et al., 2017]] ; [[#Venter--2018|Venter et al., 2018]] ), where herbivory and fire regimes are altered ( [[#O’Connor--2014|O’Connor et al., 2014]] ; [[#Archer--2017|Archer et al., 2017]] ; see also discussion on fire and herbivory in [[IPCC:Wg2:Chapter:Chapter-2#2.4.3.1|Section 2.4.3.1]] ). In some cases, woody increase has been balanced locally by changes in runoff ( [[#Trichon--2018|Trichon et al., 2018]] ) or by land clearing and fuel wood harvesting, as seen in western Niger, northern Nigeria, and at the periphery of major towns (Montagné et al., 2016).

'''Table CCP3.1 |''' Observed ecological changes in drylands.

{| class="wikitable"
|-
! '''Region'''

! '''Observed change'''

! '''Climate change factors'''

! '''Attribution to climate change'''

! '''Non-climate change factors'''

! '''Confidence in observed change'''

! '''References'''

|-
| colspan="6"| ''Hyper-arid''

|
|-
| Asian hyper-arid regions (Gobi)

| Loss of shallow rooted desert plants

| Increase in extreme warm temperatures

|
| ''medium''

| [[#Li--2015|Li et al. (2015)]]

|-
| rowspan="3"| North America—Mojave Desert

| Loss of mesic bird species

| Decreased rainfall

| Yes. Analyses of causal factors find decreased rainfall more important than non-climate factors.

| Livestock, human-ignited fires

| ''medium''

| [[#Iknayan--2018|Iknayan and Beissinger (2018)]] ; [[#Riddell--2019|Riddell et al. (2019)]]

|-
| Decline of desert tortoise ( ''Gopherus agassizii'' ) population by 90% from 1993 to 2012 at one site in the Mojave

| Decreased rainfall

|
| [[#Lovich--2014|Lovich et al. (2014)]]

|-
| Reduced perennial vegetation cover, including trees and cacti, in the Mojave and Sonoran deserts of the southwestern USA

| Increased temperature, decreased rainfall, wildfire

|
| Land use change, invasive plant species

| ''high''

| [[#Defalco--2010|Defalco et al. (2010)]] ; [[#Munson--2016b|Munson et al. (2016b)]] ; [[#Conver--2017|Conver et al. (2017)]]

|-
| colspan="6"| ''Arid''

|
|-
| rowspan="2"| African Sahel

| Woody cover increase in parts of the Sahel

| Increase in rainfall since the mid-1990s (compared to 1968–1993)and increased CO 2

|
| Restoration planting, agroforestry

| ''high''

|
|-
| Increase in grass production across the Sahel

| Increases in rainfall since the mid-1990s (compared to 1968–1993) and increased CO 2

|
| ''medium''

| Hiernaux et al. (2009a; 2009b); [[#Dardel--2014|Dardel et al. (2014)]] ; Venter et al. (2018); [[#Zhang--2018|Zhang et al. (2018)]] ; [[#Brandt--2019|Brandt et al. (2019)]] ; [[#Bernardino--2020|Bernardino et al. (2020)]]

|-
| rowspan="2"|
| Decline of mesic tree species at field sites across the Sahel

| Decreased rainfall from 1901 to 2002 increased temperature

| Yes. Multivariate statistical analyses find climate factors more important than non-climate factors.

| Land clearing for cropland expansion,

increased pressure on wood resources (rural demography, urbanisation)

| ''high''

| [[#Gonzalez--2001|Gonzalez (2001)]] ; [[#Wezel--2006|Wezel and Lykke (2006)]] ; [[#Maranz--2009|Maranz (2009)]] ; Gonzalez et al. (2012); [[#Hänke--2016|Hänke et al. (2016)]] ; [[#Kusserow--2017|Kusserow (2017)]] ; Ibrahim et al. (2018); Zida et al. (2020b)

|-
| Increased tree mortality at field sites across the Sahel

| Decreased rainfall from 1901 to 2002, increased temperature

| Yes. Multivariate statistical analyses find climate factors more important than non-climate factors.

| Agricultural expansion, modified runoff on shallow soils

| ''high''

| [[#Helldén--1984|Helldén (1984)]] ; Gonzalez, (2001); [[#Wezel--2006|Wezel and Lykke (2006)]] ; [[#Maranz--2009|Maranz (2009)]] ; Vincke et al. (2010); [[#Hänke--2016|Hänke et al. (2016)]] ; [[#Trichon--2018|Trichon et al. (2018)]] ; Zwarts et al. (2018); [[#Wendling--2019|Wendling et al. (2019)]] ; [[#Bernardino--2020|Bernardino et al. (2020)]] ; [[#Zida--2020a|Zida et al. (2020a)]]

|-
|
| Latitudinal biome shift of the Sahel

| Decreased rainfall, increased temperature

| Yes. Multivariate statistical analyses find climate factors more important than non-climate factors.

|
| ''high''

| [[#Boudet--1977|Boudet (1977)]] ; [[#Tucker--1999|Tucker and Nicholson (1999)]] ; Gonzalez, (2001); [[#Hiernaux--2006|Hiernaux and Le Houérou (2006)]] ; [[#Hiernaux--2009a|Hiernaux et al. (2009a)]] ; [[#Maranz--2009|Maranz (2009)]] ; Gonzalez et al. (2012)

|-
| Namib desert

| Increase in woody plant cover and a shift of mesic species into more arid regions

| Increase in amount of fog from westward expansion of convective rainfall and increase in number of extreme rainfall events; elevated CO 2 and warming effects on the Benguela upwelling system

|
| ''medium''

| [[#Morgan--2004|Morgan et al. (2004)]] ; Haensler et al. (2010); [[#Donohue--2013|Donohue et al. (2013)]] ; [[#Rohde--2019|Rohde et al. (2019)]]

|-
| rowspan="3"| Southern Africa— Nama-Karoo

|
| Shifting rainfall seasonality (debate over whether it is cyclical or directional); elevated CO 2

|
| ''medium''

| [[#Du%20Toit--2014|Du Toit and O’Connor (2014)]] ; Du Toit et al. (2015); Masubelele et al. (2015a; 2015b)

|-
| Eastern Karoo has experienced a significant increase in the end of the growing season length

| Shift in rainfall seasonality and increase in Mean Annual Precipitation

|
| ''low''

| [[#Davis-Reddy--2018|Davis-Reddy (2018)]]

|-
| Woody encroachment observed throughout the Nama-Karoo in valley bottoms, ephemeral stream banks and the slopes of Karoo hills

| Rising concentration of CO 2

|
| Changing land use and herbivore management

| ''medium''

| [[#Polley--1997|Polley et al. (1997)]] ; [[#Morgan--2004|Morgan et al. (2004)]] ; [[#Donohue--2013|Donohue et al. (2013)]] ; Ward et al. (2014); Masubelele et al. (2015a); [[#Hoffman--2018|Hoffman et al. (2018)]]

|-
| Southern Africa— Succulent Karoo

| Range shift in tree aloe ''Aloidendron dichotomum'' with mortality in the warmer and drier range and increase in recruitment in the cooler southern range, populations have positive growth rates, possibly due to warming, although this finding has been challenged

| Warming and drying

|
| ''medium''

| [[#Foden--2007a|Foden et al. (2007a)]] ; [[#Jack--2016|Jack et al. (2016)]]

|-
| rowspan="3"| Northern Africa—Morocco

| Increased vulnerability of oases and reduced ecosystem service provision

| High temperature and reduced precipitation causing soil and water salinisation, drying up of surface water; hot winds and sandstorms

|
| Agricultural growth, high population growth and unregulated and indiscriminate land development

| ''medium''

| [[#Karmaoui--2014|Karmaoui et al. (2014)]]

|-
| Reduced surface water availability

| Increased temperature and reduced precipitation

|
| High demand (population growth) and land use change

| ''medium''

| [[#Rochdane--2012|Rochdane et al. (2012)]] ; [[#Choukri--2020|Choukri et al. (2020)]]

|-
| Reduction of resilience of ''Abies pinasapo–Cedrus atlantica'' forests to subsequent droughts

| Successive droughts

|
| ''medium''

| [[#Navarro-Cerrillo--2020|Navarro-Cerrillo et al. (2020)]]

|-
| rowspan="3"| North American drylands

| Drought adapted species are increasing in Chihuahuan deserts

| Increase in aridity and increased interannual variation in climate trends

|
| ''medium''

| [[#Collins--2015|Collins and Xia (2015)]] ; [[#Rudgers--2018|Rudgers et al. (2018)]]

|-
| Widespread woody plant encroachment; ''Prosopis'' sp. encroachment in arid desert regions (Chihuahuan and Sonoran Desert) at a rate of ~3% per decade

| Increasing temperature, elevated CO 2 and changing rainfall

|
| Fire suppression and altered grazing/browsing regimes

| ''high''

| [[#Caracciolo--2016|Caracciolo et al. (2016)]] ; [[#Archer--2017|Archer et al. (2017)]]

|-
| Plant desert community shift changes the albedo through the reduction in dark biocrusts

| Warming and drought

|
| ''medium''

| Rutherford et al. (2000)

|-
| rowspan="4"| South Chihuahuan Desert— North and Central Mexico

| Shrub encroachment of grassland ( ''Berberis trifoliolata'' , ''Ephedra aspera'' , ''Larrea tridentata'' ) changes dominant species in shrub areas; loss of less resistant shrubby species ( ''Leucophyllum laevigatum'' , ''Lindleya mespiloides'' , ''Setchellanthus caeruleu'' ); shrub encroachment of mesic and temperate areas

| Decreased rainfall, increase in temperature and

increase CO 2

|
| Urban growth, mechanised agriculture and changes in land use

| ''high''

| [[#Pérez-Sánchez--2011|Pérez-Sánchez et al. (2011)]] ; [[#Castillón--2015|Castillón et al. (2015)]] ; [[#Sosa--2019|Sosa et al. (2019)]]

|-
| Shifts in soil microbial community to being more abundant in fungi (Ascomycota and Pleosporales)

| Decreased rainfall and increase in temperature

|
| Changes in land use

| ''low''

| [[#Vargas-Gastélum--2015|Vargas-Gastélum et al. (2015)]]

|-
| Limited ecological connectivity of shrubby populations

| Decreased rainfall and increase in temperature

|
| ''medium''

| [[#Sosa--2019|Sosa et al. (2019)]]

|-
| Loss of cacti species ( ''Echinocactus platyacanthus'' , ''Pediocactus bradyi'' , ''Coryphantha werdermannii'' , ''Astrophytum'' ) due to decline in physiological performance, loss of seed banks and lower germination rates

| Decreased rainfall and increase in temperature

|
| Cattle grazing, looting

| ''high''

| [[#Aragón-Gastélum--2014|Aragón-Gastélum et al. (2014)]] ; Shryock et al. (2014); [[#Martorell--2015|Martorell et al. (2015)]] ; [[#Carrillo-Angeles--2016|Carrillo-Angeles et al. (2016)]] ; [[#Aragón-Gastélum--2018|Aragón-Gastélum et al. (2018)]]

|-
| Arid and semiarid territories in Argentina

| Decreases in vegetation indexes

| Decreased rainfall

|
| Human-induced land degradation

| ''low''

| Barbosa et al. (2015)

|-
| Argentina Chaco Region

| Dryland salinity

| Changes in rainfall

|
| Land use change, overexploitation of water resources

| ''medium''

| [[#Amdan--2013|Amdan et al. (2013)]] ; [[#Marchesini--2017|Marchesini et al. (2017)]]

|-
| South America Arid Diagonal

| Marked reduction in streamflow from the Andes mountain ‘water towers’ due to the persistent reduction in precipitation

| Decrease in precipitation in the upper Andes; the unprecedented 10-year extreme dry period has been called the ‘Mega- drought’

|
| ''high''

| [[#Bianchi--2017|Bianchi et al. (2017)]] ; [[#Rivera--2018|Rivera and Penalba (2018)]] ; [[#Masiokas--2019|Masiokas et al. (2019)]] ; [[#Rodríguez-Morales--2019|Rodríguez-Morales et al. (2019)]]

|-
| South American Andes

| Extensive glacier retreat across the Andes

| Increasing sub-continental temperature and regional reduction in snow precipitation

|
| ''high''

| [[#Dussaillant--2019|Dussaillant et al. (2019)]] ; [[#Falaschi--2019|Falaschi et al. (2019)]] ; [[#Masiokas--2019|Masiokas et al. (2019)]]

|-
| rowspan="2"| Patagonian Andes

| Widespread tree mortality of ''Austrocedrus'' and ''Nothofagus'' forests in the dry ecotone forest-steppe across Patagonia

| Increase in extreme drought events

|
| ''high''

| [[#Rodríguez-Catón--2019|Rodríguez-Catón et al. (2019)]]

|-
| Increase in elevation of the upper-forest ''Nothofagus'' treeline across Patagonia

| Increase in temperature and duration of the growing season at high elevation in the Patagonian Andes

|
| ''high''

| Srur et al. (2016; 2018)

|-
| Central Asian arid lands

| Shrub encroachment into arid grasslands within the past 10 years

| Temperature of central Asian arid regions experienced a sharp increase in 1997 and has been in a state of high variability since then

|
| ''medium''

| [[#Li--2015|Li et al. (2015)]]

|-
| Loess Plateau, China

| Widespread vegetation greening in the Loess Plateau region; soil moisture declining widely, and deficit in forests and orchards; Yellow River runoff declining

| Significant warming, slight increase in precipitation

|
| Land use and cover change, ecological restoration, mainly induced by Grain for Green Project

| ''high''

| [[#Jia--2015|Jia et al. (2015)]] ; [[#Wang--2015|Wang et al. (2015)]] ; [[#Deng--2016|Deng et al. (2016)]] ; [[#Jiao--2016|Jiao et al. (2016)]]

|-
| The Three-River Source Region of the Tibetan Plateau, China

| Runoff increases, total water storage and groundwater increasing, Net Primary Productivity increase

| Precipitation increasing and evapotranspiration slightly decreasing

|
| Grassland protection

| ''high''

| Xu et al. (2019)

|-
| colspan="6"| ''Semiarid''

|
|-
| Australian arid lands

| Widespread greening

| Elevated CO 2

|
| ''medium''

| [[#Donohue--2013|Donohue et al. (2013)]]

|-
| African savanna

| Doubling of tree cover from 1940–2010 in South Africa, changing land use and 20% increase in spread of woody areas into previously open areas in the last 20 years

| Warming, elevated CO 2 , altered rainfall regimes

|
| Removal of mega-herbivores, fire suppression, changed herbivore regime

| ''high''

| [[#Skowno--2017|Skowno et al. (2017)]] ; [[#Stevens--2017|Stevens et al. (2017)]] ; Venter et al. (2018); García Criado et al. 2020)

|-
| African savanna

| Widespread increase in tree cover across Africa with only three countries across the continent experiencing a net decline in tree cover

| Warming, changing rainfall, mention of CO 2

|
| Fire suppression

| ''high''

| Venter et al. (2018)

|-
| African savanna

| Biodiversity responses to changes in vegetation structure (woody encroachment) causing declines in functional groups that are open area specialists, records for birds, rodents, termites, mammals, insects

| Woody encroachment

|
| ''medium''

| [[#Blaum--2007|Blaum et al. (2007)]] ; [[#Blaum--2009|Blaum et al. (2009)]] ; [[#Sirami--2012|Sirami and Monadjem (2012)]] ; [[#Gray--2013|Gray and Bond (2013)]] ; [[#Péron--2015|Péron and Altwegg (2015)]] ; [[#Smit--2015|Smit and Prins (2015)]]

|-
| African semiarid regions (savanna)

| Reduced tourism experience due to woody encroachment

| Woody encroachment

|
| ''low''

| [[#Gray--2013|Gray and Bond (2013)]]

|-
| rowspan="3"| North American drylands – sagebrush steppes

| Sagebrush steppes are being invaded by non-native grasses

| Increase in temperature and favourable climates

|
| ''high''

| Bradley et al. (2016); [[#Hufft--2016|Hufft and Zelikova (2016)]] ; [[#Chambers--2018|Chambers (2018)]]

|-
| Shrub encroachment,( ''Prosopis glandulosa'' , ''Juniper ashei'' and ''Juniper pinchotti)'' occurring in the semiarid grasslands of the southern Great Plains at a rate of ~8% per decade

| Increasing temperature, elevated CO 2 and changing rainfall

|
| Fire suppression and altered grazing/browsing regimes

| ''high''

| [[#Caracciolo--2016|Caracciolo et al. (2016)]] ; [[#Archer--2017|Archer et al. (2017)]]

|-
| Woody encroachment in sagebrush steppes (cold deserts) ( ''Juniper occidentalis'' ) at a rate of 2% per decade

| Warming and associated decline in snowpack, less precipitation falling as snow and an increase in the rain fraction in winter

|
| ''high''

| [[#Chambers--2014|Chambers et al. (2014)]] ; [[#Mote--2018|Mote et al. (2018)]]

|-
| Central Mexico

| Desertification (as decreases in vegetation indexes)

| Decreased rainfall and increase in temperature

|
| Land use change and intensification

| ''medium''

| [[#Becerril-Pina--2015|Becerril-Pina et al. (2015)]] ; [[#Noyola-Medrano--2017|Noyola-Medrano and Martínez-Sías (2017)]]

|-
| Chinese drylands

| Widespread greening trend of vegetation in China over the last three decades; regional differences

| Warming, CO 2 increase

Rising atmospheric CO 2 concentration and nitrogen deposition are identified as the most likely causes of the greening trend in China, explaining 85% and 41% of the average growing season Leaf Area Index trend

Negative impacts of climate change in north China and Inner Mongolia and and positive impacts in the Qinghai-Xizang plateau

|
| Ecological protection

| ''medium''

| [[#Piao--2015|Piao et al. (2015)]]

|-
| colspan="6"| ''Dry subhumid''

|
|-
| African mesic savannas

| Forest expansion into mesic savannas

| Increased rainfall, elevated CO 2

|
| Fire suppression

| ''medium''

| [[#Baccini--2017|Baccini et al. (2017)]] ; Aleman et al. (2018)

|-
| South American cerrado

| 8% rate of woody cover increase

| Elevated CO 2

|
| Fire exclusion

| ''high''

| [[#Stevens--2017|Stevens et al. (2017)]] ; [[#Rosan--2019|Rosan et al. (2019)]]

|-
| South American cerrado

| Expansion of forest into cerrado

| Elevated CO 2

|
| Fire exclusion

| ''high''

| [[#Passos--2018|Passos et al. (2018)]] ; [[#Rosan--2019|Rosan et al. (2019)]]

|-
| Australian savannas

| 2% rate of woody cover increase and greening of drylands

|
| ''high''

| [[#Donohue--2013|Donohue et al. (2013)]] ; [[#Stevens--2017|Stevens et al. (2017)]] ; [[#Bernardino--2020|Bernardino et al. (2020)]]

|}

<div id="CCP3.2.1.5" class="h3-container"></div>

<span id="ccp3.2.1.5-tree-death-and-woody-cover-decline"></span>
==== CCP3.2.1.5 Tree Death and Woody Cover Decline ====

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Field measurements have also detected tree mortality and loss of mesic tree species at some Sahel sites during drought periods ( [[#Gonzalez--2012|Gonzalez et al., 2012]] ; [[#Kusserow--2017|Kusserow, 2017]] ; [[#Brandt--2018|Brandt et al., 2018]] ; [[#Ibrahim--2018|Ibrahim et al., 2018]] ; [[#Trichon--2018|Trichon et al., 2018]] ; [[#Zwarts--2018|Zwarts et al., 2018]] ; [[#Bernardino--2020|Bernardino et al., 2020]] ; [[#Zida--2020|Zida et al., 2020]] ) and a reduction of mesic species in favour of drought-tolerant species ( ''high confidence'' ) ( [[#Hänke--2016|Hänke et al., 2016]] ; [[#Kusserow--2017|Kusserow, 2017]] ; [[#Ibrahim--2018|Ibrahim et al., 2018]] ; [[#Trichon--2018|Trichon et al., 2018]] ; [[#Dendoncker--2020|Dendoncker et al., 2020]] ; [[#Zida--2020|Zida et al., 2020]] b), with attribution to climate change ( [[#Gonzalez--2012|Gonzalez et al., 2012]] ). Furthermore, vegetation productivity per unit of rainfall showed a net decline of 4% in the period 2000–2015 across drylands globally, with the greatest net declines in Africa (16%) and Asia (33%) ( [[#Abel--2021|Abel et al., 2021]] ), but with location-specific increases in vegetation-rainfall sensitivity, for example, in southern and eastern Africa and parts of the Sahel. Furthermore, NDVI declines were reported across the Sahel from 1999 to 2015 ( [[#Yuan--2019|Yuan et al., 2019]] ; [[#Zida--2020a|Zida et al., 2020a]] ). However, field site monitoring showed a strong regeneration of the decimated woody populations except on shallow soil where the runoff system had evolved towards a web of gullies ( [[#Hiernaux--2009a|Hiernaux et al., 2009a]] ; [[#Trichon--2018|Trichon et al., 2018]] ; [[#Wendling--2019|Wendling et al., 2019]] ) .

Other site-specific impacts include tree mortality in southwestern Morocco ( [[#Le%20Polain%20de%20Waroux--2012|Le Polain de Waroux and Lambin, 2012]] ), mortality of ''Austrocedrus'' and ''Nothofagus'' forests in the dry Patagonia forest-steppe ( [[#Rodríguez-Catón--2019|Rodríguez-Catón et al., 2019]] ) and a tree range contraction of ''Aloidendron dichotmum'' in southern Africa ( [[#Foden--2007b|Foden et al., 2007b]] ). In Morocco, tree mortality was most highly correlated to an increase in aridity, measured by the Palmer Drought Severity Index (PDSI), which showed a statistically significant increase since 1900 due to climate change ( [[#Dai--2004|Dai et al., 2004]] ; [[#Esper--2007|Esper et al., 2007]] ; [[#Dai--2011|Dai, 2011]] ).

In deserts of the southwestern USA, a drought since 2000, mainly due to climate change ( [[#Williams--2020|Williams et al., 2020]] ), together with land use change, invasive plant species and wildfire ( [[#Syphard--2017|Syphard et al., 2017]] ), has led to reductions in native desert plant species ( [[#Defalco--2010|Defalco et al., 2010]] ; [[#Conver--2017|Conver et al., 2017]] ) and perennial vegetation cover ( [[#Munson--2016a|Munson et al., 2016a]] ; 2016b). An increase in invasive exotic grasses has increased wildfires in these desert ecosystems in which fire had been rare ( [[#Brooks--2006|Brooks and Matchett, 2006]] ; [[#Abatzoglou--2011|Abatzoglou and Kolden, 2011]] ; [[#Hegeman--2014|Hegeman et al., 2014]] ; Horn and St. Clair, 2017). In the Mojave Desert in the USA, a loss of bird biodiversity has also been detected and attributed to increased aridity caused by climate change ( [[#Iknayan--2018|Iknayan and Beissinger, 2018]] ; [[#Riddell--2019|Riddell et al., 2019]] ).

<div id="CCP3.2.1.6" class="h3-container"></div>

<span id="ccp3.2.1.6-change-in-herbaceous-cover"></span>
==== CCP3.2.1.6 Change in Herbaceous Cover ====

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Changes in aridity ( [[#Rudgers--2018|Rudgers et al., 2018]] ) have caused some expansion of dominant grasses (often invasive) into desert shrublands. The spread of invasive ''Bromus tectorum'' may be enhanced by altered precipitation and freeze–thaw cycles ( ''low confidence'' ) ( [[#Collins--2015|Collins and Xia, 2015]] ; [[#Rudgers--2018|Rudgers et al., 2018]] ). Arid grassland has expanded (between 10–100 km) into the eastern Karoo, South Africa ( ''high confidence'' ) ( [[#du%20Toit--2015|du Toit et al., 2015]] ; [[#Masubelele--2015a|Masubelele et al., 2015a]] ; 2015b). Observations from 100-year-old grazing trials demonstrate that the increase in grassiness is a product of shift in rainfall seasonality and an increase in rainfall ( [[#Du%20Toit--2014|Du Toit and O’Connor, 2014]] ; [[#du%20Toit--2015|du Toit et al., 2015]] ; 2018; [[#Masubelele--2015a|Masubelele et al., 2015a]] ;, 2015b). These changes are causing an increase in fire frequency in these seldom burnt areas ( [[#du%20Toit--2015|du Toit et al., 2015]] ). The Sahara was suggested to have expanded 10% from 1902 to 2013 ( [[#Thomas--2018|Thomas and Nigam, 2018]] ), although herbaceous vegetation production has increased in general in the Sahel since the dry 1980s ( [[#Eklundh--2003|Eklundh and Olsson, 2003]] ; [[#Anyamba--2005|Anyamba and Tucker, 2005]] ; [[#Herrmann--2005|Herrmann et al., 2005]] ; [[#Hutchinson--2005|Hutchinson et al., 2005]] ; [[#Olsson--2005|Olsson et al., 2005]] ; [[#Fensholt--2006|Fensholt et al., 2006]] ; [[#Dardel--2014|Dardel et al., 2014]] ; [[#Hiernaux--2016|Hiernaux et al., 2016]] ; [[#Stith--2016|Stith et al., 2016]] ; [[#Benjaminsen--2019|Benjaminsen and Hiernaux, 2019]] ; [[#Hiernaux--2020|Hiernaux and Assouma, 2020]] ).

Trends of land degradation ( [[IPCC:Wg2:Chapter:Chapter-16#16.4.1.2|Section 16.4.1.2]] ) and desertification (as demonstrated by loss of cover or reduced vegetation productivity) as an impact of changing climatic trends have been reported in Burkina Faso ( [[#Zida--2020|Zida et al., 2020]] ), the northwestern regions of China during 1975–1990 ( [[#Zhang--2020|Zhang et al., 2020]] ) in Afghanistan ( [[#Savage--2009|Savage et al., 2009]] ), Iran (Mahmoudi et al., 2011; [[#Kamali--2017|Kamali et al., 2017]] ), Argentina ( [[#Barbosa--2015|Barbosa et al., 2015]] ) and India ( [[#Javed--2012|Javed et al., 2012]] ). Encroachment, re-greening and an increase of unpalatable plant species into rangeland areas (e.g., in East Africa and southern Africa’s Kalahari) all contribute to dryland degradation through the loss of open ecosystems and their services ( [[#Reed--2015|Reed et al., 2015]] ; Le et al., 2016; [[#Chen--2019b|Chen et al., 2019b]] ).

<div id="CCP3.2.1.7" class="h3-container"></div>

<span id="ccp3.2.1.7-sand-and-dust-storms"></span>
==== CCP3.2.1.7 Sand and Dust Storms ====

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Soil dust emissions are highly sensitive to changing climate conditions but also to changing land use and management practices ( ''high confidence'' ). Distinguishing between the effects of these drivers is not straightforward, even in well-documented locations ( [[#Middleton--2019|Middleton, 2019]] ). There is ''limited evidence'' and ''low agreement'' about the impacts of climate change on sand and dust storms (SDS), with studies pointing to either substantial increases (+300%) or decreases (-60%) ( [[#Boucher--2013|Boucher et al., 2013]] ). Current climate models cannot adequately model the impact of climate change on SDS activity ( [[#Mirzabaev--2019|Mirzabaev et al., 2019]] ). However, there is ''high confidence'' that land degradation, loss of vegetative cover and drying of water bodies in semiarid and arid areas will contribute to sand and dust activity ( [[#Mirzabaev--2019|Mirzabaev et al., 2019]] ).

SDS remain a major concern for desert areas under conditions of climate change and desertification ( [[#Middleton--2017|Middleton, 2017]] ). Only about 20% of deserts are covered by sand, but desert SDS provide an important feedback mechanism to climate ( [[#Pu--2017|Pu and Ginoux, 2017]] ), with literature showing that some areas have very frequent dust days (Figure CCP3.2; [[#Ginoux--2012|Ginoux et al., 2012]] ). In some locations, such as the USA, desert dust can be deposited downwind on snowpacks, hastening snowmelt and altering river hydrology ( [[#Painter--2010|Painter et al., 2010]] ). Deserts and other natural dryland surfaces produced 75–90% of atmospheric dust globally in the early 21st century, with the remainder from agricultural and other land dominated by human land use ( [[#Ginoux--2012|Ginoux et al., 2012]] ; [[#Stanelle--2014|Stanelle et al., 2014]] ).

<div id="_idContainer010" class="Figure"></div>

[[File:6b5a560e77132252ec5fc500c1c930da IPCC_AR6_WGII_Figure_CCP3_002.png]]

'''Figure CCP3.2 |''' '''Frequency of high dust days (dust optical depth &gt;0.''' '''2) during the dust season, based on 2003–2009 remote sensing, the most recent data analysed, and divided into areas primarily under agriculture and areas dominated by natural land cover ( [[#Ginoux--2012|Ginoux et al., 2012]] ).''' Dust seasons: Africa (North), Year-round; Africa (South), September–February; America (North), March–May; America (South), December–February), Asia, March–May; Australia, September–February.

Recent changes in dust emissions and their attributions vary geographically. Warming in Iran over the period 1951–2013 has been associated with an increased frequency of dust events ( [[#Alizadeh-Choobari--2018|Alizadeh-Choobari and Najafi, 2018]] ) and a trend (2000–2014) towards increased fine atmospheric mineral dust concentrations in the US southwest has been linked to increasing aridity ( [[#Hand--2017|Hand et al., 2017]] ). Conversely, increases in rainfall, soil moisture and vegetation linked to changes in circulation strength of the Indian summer monsoon since 2002 have led to a substantial reduction of dust in the Thar Desert and surrounding region, showing agreement with findings from the Sahel and the West African Monsoon ( [[#Kergoat--2017|Kergoat et al., 2017]] ). A decreasing trend in the number and intensity of SDS in spring (2007–2016) in East Asia has also responded to higher precipitation and soil moisture, related to a decrease in the intensity of the polar vortex, favouring higher vegetation cover during the period studied ( [[#An--2018|An et al., 2018]] ). Global climate change, transboundary movement of aeolian material by atmospheric flows from Central Asia, dynamics of the Caspian Sea regime, erosion, salinisation and the loss of land as a result of the placement of industrial facilities have expanded the land area prone to desertification in Russia. Desertification has been observed to some extent in 27 sub-regions of the Russian Federation on territory of more than 100 million hectares ( [[#Kust--2011|Kust et al., 2011]] ; also recently confirmed by National Report, 2019). Eastern and south-eastern regions of Kalmykia, Russia, serve as dust sources, while dust and sand masses from areas of the Black Land sometimes move far beyond to parts of Rostov, Astrakhan, Volgograd and Stavropol regions. Agricultural land in these areas can become covered with dust and sand 10 cm or more thick, with negative impacts on yields ( [[#Tsymbarovich--2020|Tsymbarovich et al., 2020]] ). High dust day frequency is also occurring in the High Latitude Dust (HLD) source areas not reported in Figure CCP3.2, such as in Iceland, Patagonia, Canada, Alaska and, based on ''in situ'' measurements, in Antarctica ( [[#Dagsson-Waldhauserová--2014|Dagsson-Waldhauserová et al., 2014]] ; [[#Bullard--2016|Bullard et al., 2016]] ; [[#Dagsson-Waldhauserova--2019|Dagsson-Waldhauserova and Meinander, 2019]] ; [[#Bachelder--2020|Bachelder et al., 2020]] ). Active HLD sources cover at least 500,000 km 2 and produce at least 5% of global dust budget ( [[#Bullard--2016|Bullard et al., 2016]] ). HLD has negative impacts on the cryosphere via albedo changes and snow/ice melting ( [[#Boy--2019|Boy, 2019]] ; [[#Dagsson-Waldhauserova--2019|Dagsson-Waldhauserova and Meinander, 2019]] ).

<div id="CCP3.2.1.8" class="h3-container"></div>

<span id="ccp3.2.1.8-water-scarcity"></span>
==== CCP3.2.1.8 Water Scarcity ====

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Climate change and desertification have been linked to water loss ( [[#Bayram--2014|Bayram and Öztürk, 2014]] ; [[#Schwilch--2014|Schwilch et al., 2014]] ; [[#Mohamed--2016|Mohamed et al., 2016]] ), decreases in water quantity for irrigation and contamination of surface water bodies ( [[#Middleton--2017|Middleton, 2017]] ). Increased runoff in areas in the Sahel with shallow soils increased water flows to lakes and the recharge of water tables ( [[#Favreau--2009|Favreau et al., 2009]] ; [[#Gardelle--2010|Gardelle et al., 2010]] ; [[#Descroix--2013|Descroix et al., 2013]] ; [[#Kaptué--2015|Kaptué et al., 2015]] ; [[#Gal--2017|Gal et al., 2017]] ). Water scarcity ( [[IPCC:Wg2:Chapter:Chapter-16#16.5.2.3.7|Section 16.5.2.3.7]] ) was among the first impacts of climate change recognised in North African countries such as Morocco which have extensive dryland areas, with countries such as Turkey, Libya, USA and China carrying out large-scale water transfer projects ( [[#Sternberg--2016|Sternberg, 2016]] ; [[#Stringer--2021|Stringer et al., 2021]] ). The decrease in water availability in Morocco was substantial in terms of both surface water supply ( [[#Rochdane--2012|Rochdane et al., 2012]] ; [[#Choukri--2020|Choukri et al., 2020]] ) and groundwater ( [[#Bahir--2020|Bahir et al., 2020]] ), threatening agricultural production.

<div id="CCP3.2.2" class="h2-container"></div>

<span id="ccp3.2.2-observed-impacts-of-climate-change-on-human-systems-in-desert-and-semiarid-areas"></span>
=== CCP3.2.2 Observed Impacts of Climate Change on Human Systems in Desert and Semiarid Areas ===

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Climate change and desertification, alongside other drivers of degradation, reduce dryland ecosystem services, leading to losses of biodiversity, water, food and impacts on human health (Section [[#CCP4.2.3|CCP4.2.3]] ) and well-being ( ''high confidence'' ) ( [[#Mirzabaev--2019|Mirzabaev et al., 2019]] ) resulting in disruption to the economic structures and cultural practices of affected communities ( [[#Elhadary--2014|Elhadary, 2014]] ; [[#Middleton--2017|Middleton, 2017]] ).

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<span id="ccp3.2.2.1-sand-and-dust-storms"></span>
==== CCP3.2.2.1 Sand and Dust Storms ====

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Desertification and SDS can cause substantial socioeconomic damage in drylands ( [[#UNEP--1992|UNEP, 1992]] ; [[#Opp--2021|Opp et al., 2021]] ) over both the short and long term. Short-term impacts occur on health, food production systems, infrastructure (damaging buildings, energy systems and communications), transport and related economic productivity, air and road traffic, and costs incurred in clearing sand and dust from deposition areas ( [[#Mirzabaev--2019|Mirzabaev et al., 2019]] ). In the Arab region increasing frequency of SDS events is projected to further exacerbate water scarcity and drought ( [[#ESCWA--2017|ESCWA, 2017]] ). Longer-term costs include loss of ecosystem services, biodiversity and habitat, chronic health problems, soil erosion and reduced soil quality (particularly through nutrient losses and deposition of pollutants), and disruption of global climate regulation ( [[#Middleton--2018|Middleton, 2018]] ; [[#Allahbakhshi--2019|Allahbakhshi et al., 2019]] ). Dust deposition nevertheless can offer environmental and economic benefits, bringing important nutrients that improve and sustain soil fertility (Marticorena et al., 2017). Preventing and reducing SDS entails upfront investment costs but full benefit–cost analyses of different measures compared to the costs of inaction are scarce and need to consider the likely frequency and magnitude of SDS events (Tozer and Leys, 2013).

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<span id="ccp3.2.2.2-human-health"></span>
==== CCP3.2.2.2 Human Health ====

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The potential impacts of climate change, recurrent droughts and desertification on human health in drylands include: higher risks from water scarcity (linked to deteriorating surface and ground water quality and water-borne diseases; [[#Stringer--2021|Stringer et al., 2021]] ), food insecurity and malnutrition ( [[IPCC:Wg2:Chapter:Chapter-16#16.2.3.4|Section 16.2.3.4]] ) in the absence of sufficient imports, respiratory, cardiovascular and infectious diseases caused by SDS ( [[#Mirzabaev--2019|Mirzabaev et al., 2019]] ), potential displacement and migration and mental health consequences (Chapter 7; [[#Stringer--2021|Stringer et al., 2021]] ) and heat stress ( [[#Dunne--2013|Dunne et al., 2013]] ; [[#Zhao--2015|Zhao et al., 2015]] ; [[#Russo--2016|Russo et al., 2016]] ). SDS negatively impact human health through various pathways, causing respiratory, cardiovascular diseases and facilitating infections ( ''high confidence'' ) ( [[#Díaz--2017|Díaz et al., 2017]] ; [[#Goudarzi--2017|Goudarzi et al., 2017]] ; [[#Allahbakhshi--2019|Allahbakhshi et al., 2019]] ; [[#Münzel--2019|Münzel et al., 2019]] ). SDS can cause mortality and injuries related to transport accidents ( [[#Goudie--2014|Goudie, 2014]] ). Research from China suggests that prenatal exposure to SDS can affect children’s cognitive function ( [[#Li--2018|Li et al., 2018]] ). The pollutants that are entrained and ingested or inhaled closely link to the land management strategies in source areas.

Droughts are among the natural hazards with the highest adverse impacts on human populations ( [[#Mishra--2010|Mishra and Singh, 2010]] ; Arias et al., 2021). Although droughts represented just 4% of hazard events, their impacts amounted to 31% of affected people (29 million) ( [[#Louvain--2019|Louvain, 2019]] ). Drought exposure relates to a higher risk of undernutrition ( [[IPCC:Wg2:Chapter:Chapter-16#16.5.2.3.6|Section 16.5.2.3.6]] ), among vulnerable populations ( [[#Kumar--2016|Kumar, 2016]] ), particularly children ( [[#IFPRI--2016|IFPRI, 2016]] ) for whom the impacts can lead to lifelong consequences through stunted growth, impaired cognitive ability and reduced future educational and work performance (UNICEF/WHO/WBG, 2019). The corresponding costs of children stunting in terms of lost economic growth can be of the order of 7% of per capita income in developing countries (Galasso and Wagstaff, 2018).

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<span id="ccp3.2.2.3-agro-ecological-food-systems-livelihoods-and-food-security"></span>
==== CCP3.2.2.3 Agro-ecological Food Systems, Livelihoods and Food Security ====

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Rising temperatures, variation in rainfall patterns and frequent extreme weather events associated with climate change have adversely affected agro-ecological food systems and pastoral systems in some drylands ( [[#Zhu--2013|Zhu et al., 2013]] ; [[#Amin--2018|Amin et al., 2018]] ), especially in developing countries ( [[#Haider--2014|Haider and Adnan, 2014]] ; [[#Ahmed--2016|Ahmed et al., 2016]] ; [[#ur%20Rahman--2018|ur Rahman et al., 2018]] ) where desertification is a key challenge to agricultural livelihoods. Recurrent droughts in recent decades, coupled with wind erosion (particularly of fine sediment which gives soil its water-holding capacity and nutrients), affected vast areas in Argentina, leading to land abandonment and agricultural fields being covered by sand and invasive plants ( [[#Abraham--2016|Abraham et al., 2016]] ). Temperature increases have contributed to reduced wheat yields in arid, semiarid and dry sub-humid zones of Pakistan ( [[#Sultana--2019|Sultana et al., 2019]] ). Agricultural production in the drylands of South Punjab is experiencing irreversible impacts since the grain formation phase has become swifter with a warmer climate, leading to improper growth and reduced yields ( [[#Rasul--2011|Rasul et al., 2011]] ).

[[#Aslam--2018|Aslam et al. (2018)]] regard climate change impacts as particularly threatening to the livestock sector, water and food security, and the economy beyond agriculture in South Punjab, particularly as yields decrease. In the livestock sector across global drylands (WGI TS.4.3.2.10), observed impacts include reduction of plant cover in rangelands, reduced livestock and crop yields, loss of biodiversity and increased land degradation and soil nutrient loss (Van de Steeg, 2012; [[#Mganga--2015|Mganga et al., 2015]] ; [[#Ahmed--2016|Ahmed et al., 2016]] ; [[#Mohamed--2016|Mohamed et al., 2016]] ; [[#Eldridge--2018|Eldridge and Beecham, 2018]] , Arias et al., 2021), as well as injury and livestock death due to SDS. This is particularly worrisome for traditional pastoralists who find themselves with fewer safety nets and more limited adaptive capacities than in the past, particularly where mobility, access and tenure rights are becoming restricted (Box CCP3.1) and where use of technologies such as mobile phones can result in mixed effects, as found in Morocco ( [[#Vidal-González--2018|Vidal-González and Nahhass, 2018]] ). Observed SDS impacts can increase food production costs and threaten sustainability more generally ( [[#Middleton--2017|Middleton, 2017]] ).

Woody plant encroachment and greening may be masking underlying land degradation processes and losses of ecosystem services, livelihood and adaptation options in pastoral livelihood systems ( [[#Reed--2015|Reed et al., 2015]] ; [[#Chen--2019a|Chen et al., 2019a]] ). Woody encroachment alters ecosystem services, particularly in rangelands, resulting in reduction of grass cover, hindering livestock production (Anadón et al. 2014), reducing water availability (Honda and Durigan 2016, [[#Stringer--2021|Stringer et al., 2021]] ) but increasing availability of wood (Mograbi et al., 2019).

<div id="CCP3.2.2.4" class="h3-container"></div>

<span id="ccp3.2.2.4-gender-differentiated-impacts"></span>
==== CCP3.2.2.4 Gender Differentiated Impacts ====

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Impacts of desertification, climate change and environmental degradation, as well as vulnerability and capacity to adapt, are gendered. Differences are determined by socially structured gender-specific roles and responsibilities, ownership of, access to and control over natural resources and technology, decision making, and capacity to cope and adapt to long-term changes ( [[#Mirzabaev--2019|Mirzabaev et al., 2019]] ; Cross-Chapter Box GENDER in Chapter 18). Assessments of the gender dimension of desertification and climate change impacts and responses are scarce, and highly context specific. For example, in many lower income countries, rural women produce most of the household food, and are responsible for food preparation and collecting fuelwood and water from increasingly distant sources ( [[#Mekonnen--2017|Mekonnen et al., 2017]] ; Droy, 2020). Drought and water scarcity particularly affect women and girls in drylands because they need to spend more time and energy collecting water and fuelwood, have less time for education or income-generating activities, and may be more exposed to violence ( [[#Sommer--2014|Sommer et al., 2014]] ) and less able to migrate as an adaptation option. Women are also commonly excluded from family and community decision making on actions to address desertification and climate change, yet their engagement in climate adaptation is critical. International policy efforts are currently seeking to better recognise and address this challenge ( [[#Okpara--2019|Okpara et al., 2019]] ).

<div id="CCP3.2.2.5" class="h3-container"></div>

<span id="ccp3.2.2.5-climate-change-migration-and-conflict"></span>
==== CCP3.2.2.5 Climate Change, Migration and Conflict ====

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Dryland populations pursuing traditional land-based livelihood options are generally mobile due to a highly fluctuating resource base (Box CCP 3.1). Many rural dwellers in drylands also move to urban areas for seasonal work, which can have positive impacts in terms of remittances. While reasons for migration vary and can be positive or negative, oppression and human rights abuses, lack of livelihood opportunities and food insecurity tend to be among the main push factors, while emerging opportunities at the rural–urban nexus present lucrative pull factors (Cross-Chapter Box MIGRATE in Chapter 7). In a survey in Libya in 2016, 80% of migrants interviewed said they had left home because of economic hardship ( [[#Hochleithner--2018|Hochleithner and Exner, 2018]] ), which in drylands under water scarcity linked to climate change, would be exacerbated.

Causes of migration and violent conflict need to be seen in a wider historical, agrarian, political, economic and environmental context, in a multi-scalar perspective integrating levels of analysis from the local to the global ( [[#Glick%20Schiller--2015|Glick Schiller, 2015]] ). Quantitative studies tend to conclude that climate change has so far not significantly impacted migration including in drylands ( [[#Owain--2018|Owain and Maslin, 2018]] ), although with some disagreement ( [[#Lima--2016|Lima et al., 2016]] ; [[#Missirian--2017|Missirian and Schlenker, 2017]] ). In a study of the climate change–migration–conflict interface, [[#Abel--2019|Abel et al. (2019)]] found limited empirical evidence supporting a link between climatic shocks, conflict and asylum-seeking for the period 2006–2015 from 157 countries. The authors found evidence of such a link for the period 2010–2012 relating to some countries affected by the Arab Spring and concluded that the impact of climate on conflict and migration is limited to specific time periods and contexts.

The same lack of general causality is largely concluded on the specific link between climate change and conflict ( [[#Buhaug--2014|Buhaug et al., 2014]] ; [[#Buhaug--2015|Buhaug et al., 2015]] ; [[#von%20Uexkull--2016|von Uexkull et al., 2016]] ; [[#Koubi--2019|Koubi, 2019]] ), but a minority of quantitative studies argue for a stronger causal association ( [[#Hsiang--2013|Hsiang et al., 2013]] ). [[#Mach--2019|Mach et al. (2019)]] found considerable agreement among experts that climate variability and change have influenced the risk of organised armed conflict within countries, but they also agreed that other factors, such as state capacity and level of socioeconomic development, played a much larger role. These factors also play a role in determining adaptation possibilities and in shaping the enabling environment ( [[IPCC:Wg2:Chapter:Chapter-8#8.5.2|Section 8.5.2]] ).

Qualitative case studies tend to frame conflict and migration within a larger political, economic and historical context. A number of studies from African drylands find that land dispossession is a key driver of both migration and conflict resulting from large-scale resource extraction or land encroachment, often associated with processes of elite capture and marginalisation ( [[#Benjaminsen--2009|Benjaminsen and Ba, 2009]] ; [[#Benjaminsen--2009|Benjaminsen et al., 2009]] ; [[#Cross--2013|Cross, 2013]] ; [[#Glick%20Schiller--2015|Glick Schiller, 2015]] ; Nyantakyi-Frimpong and Bezner Kerr, 2017; [[#Obeng-Odoom--2017|Obeng-Odoom, 2017]] ; [[#Bergius--2020|Bergius et al., 2020]] ). By undermining livelihoods, exacerbating poverty and setting rural population groups adrift, land dispossession in the Sahel may lead to increased migration to urban areas, to rural sites of non-farm employment (e.g., mines) ( [[#Chevrillon-Guibert--2019|Chevrillon-Guibert et al., 2019]] ) or out of the country. In addition, it may lead to other types of reactions including violent resistance ( [[#Oliver-Smith--2010|Oliver-Smith, 2010]] ; [[#Cavanagh--2015|Cavanagh and Benjaminsen, 2015]] ; [[#Hall--2015|Hall et al., 2015]] ) as already seen in the Sahel in terms of the emergence of jihadist armed groups ( [[#Benjaminsen--2019|Benjaminsen and Ba, 2019]] ). Major drivers of the current crisis in Mali include decades of bureaucratic mismanagement and widespread corruption, the spill-over of jihadist groups from Algeria after the civil war there in the 1990s and the current civil war in Libya. Climate change has played a marginal role as a driver of conflicts in the Sahel ( [[#Benjaminsen--2012|Benjaminsen et al., 2012]] ; [[#Benjaminsen--2019|Benjaminsen and Hiernaux, 2019]] ) but has potential to exacerbate the situation in the future with regards to migration and conflict ( [[#Owain--2018|Owain and Maslin, 2018]] ).

<div id="box-ccp3.1" class="h2-container box-container"></div>

<span id="box-ccp3.1-pastoralism-and-climate-change"></span>
=== Box CCP3.1 | Pastoralism and climate change ===

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Pastoralism is a livestock-keeping system based on the herding of animals. Migrations often take place over long distances to track variable and unpredictable plant growth that tends to be patchy in space and variable in time ( [[#Homewood--2018|Homewood, 2018]] ). Pastoralism has a considerably lower carbon budget than other livestock-keeping systems. Research on pastoralism in the Sahel concluded that this system may be carbon neutral ( [[#Assouma--2019|Assouma et al., 2019]] ), despite contributing directly to greenhouse gas emissions via methane enteric emissions and indirectly through faeces-driven CO 2 , CH 4 and N 2 O emissions during mineralisation ( [[#Assouma--2017|Assouma et al., 2017]] ). Efforts to sedentarise and settle pastoralists in villages can lead to land degradation and higher overall emissions from the sector.

Pastoralists migrate with their animals in some of the most remote and marginal environments on the planet. Globally, mobile pastoralists number about 200 million households and use about 25% of the Earth’s landmass ( [[#Dong--2016|Dong, 2016]] ). Many pastoralists operate in non-equilibrial environments that are unstable, fluctuating and generally uncertain, and are driven more by climatic variation than livestock numbers and grazing pressure (Behnke et al., 1993). Examples of such systems are grazing areas in the dry tropics ( [[#Sandford--1983|Sandford, 1983]] ; [[#Turner--1993|Turner, 1993]] ; [[#Sullivan--2002|Sullivan and Rohde, 2002]] ; [[#Benjaminsen--2006|Benjaminsen et al., 2006]] ; [[#Hiernaux--2016|Hiernaux et al., 2016]] ) and rangelands in the Arctic ( [[#Behnke--2000|Behnke, 2000]] ; [[#Tyler--2008|Tyler et al., 2008]] ; [[#Benjaminsen--2015|Benjaminsen et al., 2015]] ; [[#Marin--2020|Marin et al., 2020]] ).

Over many generations, pastoralists have accumulated practical experience and knowledge to cope with uncertainty and value variability ( [[#Krätli--2010|Krätli and Schareika, 2010]] ), mainly through a mobile and flexible approach. While pastoralists are also at risk of climate change impacts, they may be better able to adapt to a changing climate than other land users ( [[#Davies--2008|Davies and Nori, 2008]] ; [[#Krätli--2010|Krätli and Schareika, 2010]] ; [[#Jones--2016|Jones and Gutzler, 2016]] ).

While pastoralists possess substantial adaptive capacity as a result of their Indigenous knowledge, this has been under pressure during the last few decades through continued loss of livestock corridors (essential to mobility) and pastures in general due to competing land uses, such as farming, mining, crop expansion and the establishment or extension of protected areas ( [[#Thébaud--2001|Thébaud and Batterbury, 2001]] ; [[#Brockington--2002|Brockington, 2002]] ; [[#Benjaminsen--2009|Benjaminsen and Ba, 2009]] ; [[#Upton--2014|Upton, 2014]] ; [[#Johnsen--2016|Johnsen, 2016]] ; Tappan, 2016; [[#Homewood--2018|Homewood, 2018]] ; [[#Weldemichel--2019|Weldemichel and Lein, 2019]] ; [[#Bergius--2020|Bergius et al., 2020]] ). Many of these competing land uses erect fences and exclude other uses, while property rights often privilege sedentary farming.

Modern states have typically tried to settle pastoralists and confine their movements within clearly defined boundaries, claiming that pastoral land use is neither ecologically sustainable nor economically productive. Based on such negative and often flawed views, stall-feeding and ranching are often presented by policymakers as successful models of livestock keeping in contrast to the pastoral way of life ( [[#Steinfeld--2006|Steinfeld et al., 2006]] ; [[#Chatty--2007|Chatty, 2007]] ).

Current pressures and processes of pastoral change are spatially variable and complex, and tend to result in further economic and political marginalisation of pastoralists, with adverse effects on livelihoods and landscapes. With climate change, which is projected to lead to higher temperatures and more frequent fluctuations in precipitation, maintaining flexibility and resilience in pastoral land use is essential. However, current processes of marginalisation, in addition to increased insecurity in some drylands (e.g., the Sahel), make pastoralists more vulnerable, and constrain them from fully employing their adaptive capacities ( [[#Davies--2008|Davies and Nori, 2008]] ). The skills and capacities held by pastoralists may, however, offer lessons for society at large in its struggle to adapt to climate change and deal with increased uncertainty ( [[#Davies--2008|Davies and Nori, 2008]] ; [[#Scoones--2009|Scoones, 2009]] ; [[#Nori--2019|Nori and Scoones, 2019]] ).

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