Drylands are defined by a scarcity of water. Drylands are zones where precipitation is balanced by evaporation from surfaces and by evapotranspiration by plants.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. The United Nations Environment Program defines drylands as tropical and temperate areas with an aridity index of less than 0.65."Millennium Ecosystem Assessment, 2005. Drylands Systems". Chapter 22 in: Ecosystems and Human Wellbeing: Current State and Trends, Volume 1. Island Press. Drylands can be classified into four sub-types: Dry sub-humid lands Semi-arid lands Arid lands Hyper-arid lands
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. Drylands are home to more than 2 billion people.
Drylands are complex ecosystems, whose characteristics and dynamic properties depend on many interrelated interactions between climate, soil, and vegetation.Rodríguez-Iturbe, I. and A. Porporato 2004. Ecohydrology of Water-Controlled Ecosystems: Soil Moisture and Plant Dynamics. Cambridge University Press. Drylands are highly vulnerable to climate change due to changing rainfall patterns and land degradation.
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. Dryland inhabitants' lifestyles provide global environmental benefits such as contributing to halting climate change through carbon sequestration and species conservation. Dryland biodiversity is equally important to sustainable development. Drylands also provide 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 drylands' biodiversity and recognized the severity of biodiversity loss and degradation in these ecosystems.
Climate change
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. Drylands ecosystems also feature climate tipping points.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.
From 1982 to 2015, 12.6% of the world's drylands have degraded due to anthropogenic climate change. Drylands' vulnerability to land degradation and desertification is affecting 213 million people of which the vast majority live in the Global South. 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.
Sustainable land management practices (such as mobile pastoralism), restoring degraded lands, and climate-smart agriculture can mitigate these impacts. Addressing urban expansion's indirect impacts, such as water use, on dryland habitats is also important for preserving biodiversity.
Drylands in East Africa The East African drylands cover of the land areas and are home to more than 60 million people. 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. The greatest issue in drylands, is land degradation which poses a huge danger to food security. Drylands occupy around 2 million km2 and 90% of Kenya, 75% of Tanzania, 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.
Four sub-types Dry and sub-humid lands
Countries like Burkina Faso, Botswana, Iraq, Kazakhstan, Turkmenistan and the Republic of Moldova, are 99% covered in areas of dry and sub-humid lands. The biodiversity of dry and sub-humid lands allows them to adapt to the unpredictable rainfall patterns that lead to both floods and droughts. 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: Grassland Savannahs Mediterranean climate
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.
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. Other sources insist that the concept of aridity should be included in the definition.
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: Increased variability of precipitations and their characteristics (number of rainfall days, start of rainy season, length of the season) that can be translated to an abrupt alternative between dry and humid years a shorter rainy season correlated to its late start an increase in the occurrence of dry sequences that occur randomly and are hard to forecast a tendency of maximal rains concentrated in fewer consecutive days, thus causing damage dry and violent winds associated with very scarce rainfall that prevent the building of soil moisture increased temperatures causing thermal stress that may seriously handicap human, animal, and plant life
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. 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. These adaptation strategies allow them to be more resilient to climate change.
Arid lands
Arid lands make up about 10% of the world's land and are home to 20% of the world's people. 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.
Dryland restoration Restoration is defined by IPBES as 'any intentional activities that initiates or accelerates the recovery of an ecosystem from a degraded state.' It is one of the three pillars of nature-based solutions defined by the IUCN as "actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits".IUCN (2020). Guidance for using the IUCN Global Standard for Nature-based Solutions. A user-friendly framework for the verification, design and scaling up of Nature-based Solutions. First edition. Gland, Switzerland: IUCN. Ecosystem restoration in general is also emphasized as a tool for climate mitigation and adaptation by IUCN and IPCC.IPCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, 184 pp., doi: 10.59327/IPCC/AR6-9789291691647.
Dryland restoration is often understood in two ways; either to restore a dryland to its previous functionality or to avoid further degradation. The first perspective is based on the restoration of the degraded dryland areas themselves. Restoration of a degraded dryland to its previous functionality and ecosystem state can have benefits for both humans and nature when done correctly. The second emphasises preventative and adaptive land management to support ecosystem services and functionalities. This is the presumed logic behind the extensive project in the Sahel region named the Great Green Wall supported by UNCCD (see: case studies).
FAO provides 10 practice principles to guide ecosystem restoration.Nelson, C.R., Hallett, J.G., Romero Montoya, A.E., Andrade, A., Besacier, C., Boerger, V., Bouazza, K., Chazdon, R., Cohen-Shacham, E., Danano, D., Diederichsen, A., Fernandez, Y., Gann, G.D., Gonzales, E.K., Gruca, M., Guariguata, M.R., Gutierrez, V., Hancock, B., Innecken, P., Katz, S.M., McCormick, R., Moraes, L.F.D., Murcia, C., Nagabhatla, N., Pouaty Nzembialela, D., Rosado-May, F.J., Shaw, K., Swiderska, K., Vasseur, L., Venkataraman, R., Walder, B., Wang, Z., & Weidlich, E.W.A. 2024. Standards of practice to guide ecosystem restoration – A contribution to the United Nations Decade on Ecosystem Restoration 2021-2030. Rome, FAO, Washington, DC, SER & Gland, Switzerland, IUCN CEM. https://doi.org/10.4060/cc9106en The principles include the selection and management of restoration activities at project sites, prevention of misuse of resources and unintended consequences, enabling conditions for restoration, and assessing and applying lessons learned.
Desertification distribution