Drylands

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Dryland farms and the Linares River [es] in the Castilla-La Mancha region of Spain Cueva de los casares 07.JPG
Dryland farms and the Linares River  [ es ] in the Castilla–La Mancha region of Spain

Drylands are defined by a scarcity of water. Drylands are zones where precipitation is balanced by evaporation from surfaces and by evapotranspiration by plants. [1] The United Nations Environment Program defines drylands as tropical and temperate areas with an aridity index of less than 0.65. [2] Drylands can be classified into four sub-types:

Contents

Some authorities regard hyper-arid lands as deserts (United Nations Convention to Combat Desertification) although a number of the world's deserts include both hyper-arid and arid climate zones. The UNCCD excludes hyper-arid zones from its definition of drylands.

Drylands cover 41.3% of the Earth's land surface, including 15% of Latin America, 66% of Africa, 40% of Asia, and 24% of Europe. There is a significantly greater proportion of drylands in developing countries (72%), and the proportion increases with aridity: almost 100% of all hyper-arid lands are in the developing world. Nevertheless, the United States, Australia, and several countries in Southern Europe also contain significant dryland areas. [2] Drylands are home to more than 2 billion people. [3]

Drylands are complex ecosystems, whose characteristics and dynamic properties depend on many interrelated interactions between climate, soil, and vegetation. [4] Drylands are highly vulnerable to climate change due to changing rainfall patterns and land degradation. [3]

Importance

The livelihoods of millions of people in developing countries depend highly on dryland ecosystems to ensure their food security and their well-being. Drylands, unlike more humid biomes, rely mostly on above ground water runoff for redistribution of water. [5] Dryland inhabitants' lifestyle provides global environmental benefits such as contribute to halting climate change through carbon sequestration and species conservation. Dryland biodiversity is equally important to ensuring sustainable development, along with providing significant global economic value through the provision of ecosystem services and biodiversity conservation. The UN Conference on Sustainable Development, Rio+20 held in Brazil in June 2012, stressed the intrinsic value of biological diversity and recognized the severity of global biodiversity loss and degradation of ecosystems. [6]

Climate change

Key feedbacks that could lead to dryland ecosystems crossing tipping points. SOC stands for soil organic carbon. White arrows represent positive effects and red arrows are negative effects. Fig 1.3.11 Schematic showing key feedbacks that could lead to dryland tipping..png
Key feedbacks that could lead to dryland ecosystems crossing tipping points. SOC stands for soil organic carbon. White arrows represent positive effects and red arrows are negative effects.

Climate change and human activities are causing land degradation in drylands. These factors have led to increasing droughts, desertification and soil erosion, which decreases biodiversity, soil fertility and carbon sequestration in these regions. This has negative impacts on local agriculture and food security. [7] [8] Drylands ecosystems also feature climate tipping points. [9]

From 1982-2015, 12.6 % of the world’s drylands have degraded due to anthropogenic climate change. [10] Drylands’ vulnerability to land degradation and desertification is affecting 213 million people of which the vast majority live in the Global South. [10] In recent decades, about 7.6% of global land (an area larger than Canada) has transitioned into drier conditions, either becoming more arid or shifting from non-drylands to drylands. An area half the size of Australia has transformed from once-humid landscapes into drylands. [11]

Sustainable land management practices (such as mobile pastoralism), restoring degraded lands, and climate-smart agriculture can mitigate these impacts. [12] Addressing urban expansion's indirect impacts, such as water use, on dryland habitats is also important for preserving biodiversity. [13]

Drylands in East Africa

The East African drylands cover of the land areas and are home to more than 60 million people. [14] Pastoralists who rely on cattle for both economic and cultural well-being constitute the majority of rural inhabitants in the drylands. Pastoralists use strategic movement to gain access to pasture during the dry season, using the available resources effectively. However, this is facing challenges due to demographics and climate change. [15] The greatest issue in drylands, is land degradation which poses a huge danger to food security. [16] Drylands occupy around 2 million km² and 90% of Kenya, [17] 75% of Tanzania, [18] and 67% of Ethiopia. The low level of precipitation and the high degree of variability in the climatic conditions limit the possibilities for rainfed crop production in these areas. [19]

Four sub-types

Dry and sub-humid lands

Spiny forest, Madagascar Spiny Forest, Madagascar (23985856889).jpg
Spiny forest, Madagascar

Countries like Burkina Faso, Botswana, Iraq, Kazakhstan, Turkmenistan and the Republic of Moldova, are 99% covered in areas of dry and sub-humid lands. [20] The biodiversity of dry and sub-humid lands allows them to adapt to the unpredictable rainfall patterns that lead to both floods and droughts. [21] These areas produce a large amount the world's crops and livestock. Even further than producing the vast majority of crops in the world, it is also significant because it includes many different biomes such as the following:

Semi-arid lands

Semi-arid lands can be found in several regions of the world. For instance in places such as Europe, Mexico, Southwestern parts of the U.S, Countries in Africa that are just above the equator, and several Southern countries in Asia. [22]

Brazilian semi-arid region Brazilian semi-arid region.jpg
Brazilian semi-arid region
Gestet forest in north Ethiopia Inda Abba Hadera forest.jpg
Gestet forest in north Ethiopia

Definition of semi-arid lands

Arid and semi-arid lands are defined based on the characteristics of the climate. One measure based on precipitation considers semi-arid lands as places where the annual rainfall ranges between 500 and 800mm. [23] Other sources insist that the concept of aridity should be included in the definition. [24]

Manifestations of climate change in semi-arid lands

Based on the consequences caused by the variability of climate change, dryland populations appear to be more vulnerable than others. As much of the rainfall occurs in variable extreme events that are hard to predict. The manifestation of climate change on the development of socioeconomic activities in semi-arid lands are: [25]

Adaptation and resilience

In semi-arid lands where pastoralism is the principal activity, the main adaptation measures are an earlier movement of herds, the reduction of the size of the herd, a change in the management of water, and diversification of paths of transhumance. [26] This allows breeders to safeguard their livestock and prevent huge losses as was the case in the drought of the seventies. Other adaptations include becoming proactive (engage in trade, real estate, guarding, transport) this is taking place in certain countries like Burkina Faso, Senegal, Mali, and Kenya. [26] [27] These adaptation strategies allow them to be more resilient to climate change.

Arid lands

Arid chaco Arid chaco.jpg
Arid chaco

Arid lands make up about 10% of the world's land and are home to 20% of the world's people. [28] The UNCCD defined them as having an aridity index between ~0.05-0.20.

Hyper-arid lands

These lands cover ~8% of the world and consist of areas of little to no vegetation. They receive irregular rainfall that barely surpasses 100 mm, and in some cases, they may not receive rainfall for several years. [28]

Dry land Dry land - panoramio.jpg
Dry land

See also

References

  1. ↑ Middleton and Thomas, 1997. "The World Atlas of Desertification Millennium Ecosystem Assessment (2005a). Climate Change". Chapter 13 in: Ecosystems and Human Wellbeing: Current State and Trends, Volume 1. Island Press.
  2. 1 2 "Millennium Ecosystem Assessment, 2005. Drylands Systems". Chapter 22 in: Ecosystems and Human Wellbeing: Current State and Trends, Volume 1. Island Press.
  3. 1 2 "Drylands and climate change". iucn.org. Retrieved 2026-02-02.
  4. ↑ Rodríguez-Iturbe, I. and A. Porporato 2004. Ecohydrology of Water-Controlled Ecosystems: Soil Moisture and Plant Dynamics. Cambridge University Press.
  5. ↑ Puigdefabregas, J (October 1999). "Scales and processes of water and sediment redistribution in drylands: results from the Rambla Honda field site in Southeast Spain". Earth-Science Reviews. 48 (1–2): 39–70. Bibcode:1999ESRv...48...39P. doi:10.1016/S0012-8252(99)00046-X. hdl: 10261/358465 .
  6. ↑ "Conserving Drylands Biodiversity". 9 September 2012.
  7. ↑ Yao, Jingyu; Liu, Heping; Huang, Jianping; Gao, Zhongming; Wang, Guoyin; Li, Dan; Yu, Haipeng; Chen, Xingyuan (2020-04-03). "Accelerated dryland expansion regulates future variability in dryland gross primary production". Nature Communications. 11 (1): 1665. doi:10.1038/s41467-020-15515-2. ISSN   2041-1723. PMC   7125214 .
  8. ↑ "Dryland expansion to hit food crops as planet warms". Climate Home News. 2017-04-25. Retrieved 2025-03-13.
  9. ↑ T. M. Lenton, D.I. Armstrong McKay, S. Loriani, J.F. Abrams, S.J. Lade, J.F. Donges, M. Milkoreit, T. Powell, S.R. Smith, C. Zimm, J.E. Buxton, E. Bailey, L. Laybourn, A. Ghadiali, J.G. Dyke (eds), 2023, The Global Tipping Points Report 2023. University of Exeter, Exeter, UK.
  10. 1 2 Burrell, A. L.; Evans, J. P.; De Kauwe, M. G. (2020-07-31). "Anthropogenic climate change has driven over 5 million km2 of drylands towards desertification". Nature Communications. 11 (1). doi:10.1038/s41467-020-17710-7. ISSN   2041-1723. PMC   7395722 . PMID   32737311.
  11. ↑ "The global threat of drying lands: Regional and global aridity trends and future projections". UNCCD. 2024-12-09. Retrieved 2025-03-13.
  12. ↑ IUCN. "Drylands and climate change". iucn.org. Retrieved 2025-03-13.
  13. ↑ Ren, Qiang; He, Chunyang; Huang, Qingxu; Shi, Peijun; Zhang, Da; Güneralp, Burak (25 July 2022). "Impacts of urban expansion on natural habitats in global drylands" . Nature Sustainability. 5 (10): 869–878. doi:10.1038/s41893-022-00930-8. ISSN   2398-9629.
  14. ↑ "Drylands Development, Pastoralism and Biodiversity Conservation in Eastern Africa" (PDF).{{cite web}}: line feed character in |title= at position 38 (help)
  15. ↑ Turner, Matthew D.; Schlecht, Eva (2019-08-26). "Livestock mobility in sub-Saharan Africa: A critical review". Pastoralism. 9 (1): 13. Bibcode:2019Pasto...9...13T. doi: 10.1186/s13570-019-0150-z . ISSN   2041-7136. S2CID   201642982.
  16. ↑ Bekele, Adugna Eneyew; Drabik, Dusan; Dries, Liesbeth; Heijman, Wim (September 2020). "Large scale land investments, household displacement and the effect on land degradation in semiarid agro-pastoral areas of Ethiopia". Research Gate.
  17. ↑ "Updated Link and Survey Tool Added to Supplement". JAMA Dermatology. 158 (11): 1333. 2022-09-21. doi: 10.1001/jamadermatol.2022.4185 . ISSN   2168-6068. PMC   9494260 . PMID   36129697.
  18. ↑ "Updated Link and Survey Tool Added to Supplement". JAMA Dermatology. 158 (11): 1333. 2022-09-21. doi: 10.1001/jamadermatol.2022.4185 . ISSN   2168-6068. PMC   9494260 . PMID   36129697.
  19. ↑ Omondi, Shadrack. "Drylands development, pastoralism and biodiversity conservation in Eastern Africa".{{cite journal}}: Cite journal requires |journal= (help)
  20. ↑ "What is Dry and Sub-humid Lands Biodiversity?". cbd.int. 2007-05-16. Retrieved 2019-04-11.
  21. ↑ "Dry and Sub-humid lands" (PDF). cbd.int/drylands.
  22. ↑ "What Is a Semi-Arid Climate?". Sciencing. Retrieved 2022-06-18.
  23. ↑ Kabote, Samwel J. "Impact of Climate Variability and Change on Rain-Fed Farming System in Selected Semi-Arid Areas of Tanzania".{{cite journal}}: Cite journal requires |journal= (help)
  24. ↑ Fabricius, Christo (2008). Situation Analysis of Ecosystem Services and Poverty Alleviation in arid and semi-arid Africa (PDF). Consortium for Ecosystem Services and Poverty Alleviation in arid and semi-arid Africa (CEPSA).
  25. ↑ Wade, Cheikh Tidiane; Touré, Oussouby; Diop, Mamadou (2015). Gestion des risques climatiques (PDF). Dakar: IED Afrique.
  26. 1 2 Bonnet, Bernard; Guibert, Bertrand (2013). "La contribution de l'elevage pastoral a la securite et au developpement des espaces saharo-saheliens, analyses de trajectoires de familles de pasteurs en lien avec les crises pastorales" (PDF). colloque regional de N’djamena, 27-29 mai. Archived from the original (PDF) on 2019-08-08. Retrieved 2019-08-08.
  27. ↑ DIOP, Waoundé; Beye, Assane; Dia, Néné (2017). "Essai d'évaluation des stratégies d'adaptation face aux risques climatiques sur la chaine de valeur bovine : cas du Ferlo". communication au colloque le pastoralisme dans le courant des changements globaux: defis, enjeux et perspectives.{{cite web}}: Missing or empty |url= (help)
  28. 1 2 "Soil improvement in arid and semiarid regions for sustainable development", Natural Resources Conservation and Advances for Sustainability, Elsevier, pp. 73–90, 2022-01-01, doi:10.1016/B978-0-12-822976-7.00026-0 , retrieved 2026-02-02
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