Drylands are defined by a scarcity of water. Drylands are zones where

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

is balanced by

evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when h ...

from surfaces and by

transpiration Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth ...

by plants (

evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transp ...

). The

United Nations Environment Program The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the United Nations Conference on th ...

defines drylands as

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

and

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...

areas with an

aridity index An aridity index (AI) is a numerical indicator of the degree of dryness of the climate at a given location. A number of aridity indices have been proposed (see below); these indicators serve to identify, locate or delimit regions that suffer from a ...

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. One can classify drylands into four sub-types: * Dry sub-humid lands * Demi-arid lands * Arid lands * Hyper-arid lands Some authorities regard hyper-arid lands as

desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...

s (

United Nations Convention to Combat Desertification The United Nations Convention to Combat Desertification in Those Countries Experiencing Serious Drought and/or Desertification, Particularly in Africa (UNCCD) is a Convention to combat desertification and mitigate the effects of drought through ...

- UNCCD) although a number of the world's

deserts A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...

include both hyper-arid and arid climate zones. The

UNCCD The United Nations Convention to Combat Desertification in Those Countries Experiencing Serious Drought and/or Desertification, Particularly in Africa (UNCCD) is a Convention to combat desertification and mitigate the effects of drought through ...

excludes hyper-arid zones from its definition of drylands. Drylands cover 41.3% of the earth's land surface, including 15% of

Latin America Latin America or * french: Amérique Latine, link=no * ht, Amerik Latin, link=no * pt, América Latina, link=no, name=a, sometimes referred to as LatAm is a large cultural region in the Americas where Romance languages — languages derived ...

, 66% of

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

, 40% of

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

, and 24% of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

. There is a significantly greater proportion of drylands in

developing countries A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...

(72%), and the proportion increases with

aridity A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most a ...

: almost 100% of all hyper-arid lands are in the developing world. Nevertheless, the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

, and several countries in

Southern Europe Southern Europe is the southern region of Europe. It is also known as Mediterranean Europe, as its geography is essentially marked by the Mediterranean Sea. Definitions of Southern Europe include some or all of these countries and regions: Alb ...

also contain significant dryland areas. Drylands are complex, evolving structures whose characteristics and

dynamic Dynamics (from Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' "power") or dynamic may refer to: Physics and engineering * Dynamics (mechanics) ** Aerodynamics, the study of the motion of air ** Analytical dyn ...

properties depend on many interrelated interactions between

climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

, and

vegetation Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic charac ...

Biodiversity

The livelihoods of millions of people in

depend highly on dryland

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species ('' species diversity''), and ecosystem ('' ecosystem diversity'') ...

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, and almost all their water redistribution occurs on the surface. Dryland inhabitants' lifestyle provides global environmental benefits which contribute to halt

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

, such as

carbon sequestration Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in lan ...

and species conservation. Dryland biodiversity is equally of central importance as to ensuring

sustainable development Sustainable development is an organizing principle for meeting human development goals while also sustaining the ability of natural systems to provide the natural resources and ecosystem services on which the economy and society depend. The ...

, along with providing significant global economic values through the provision of

ecosystem services Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. ...

and biodiversity products. The UN Conference on Sustainable Development

Rio+20 The United Nations Conference on Sustainable Development (UNCSD), also known as Rio 2012, Rio+20 (), or Earth Summit 2012 was the third international conference on sustainable development aimed at reconciling the economic and environmental goals ...

, held in

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

in June 2012, stressed the intrinsic value of

biological Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary in ...

diversity Diversity, diversify, or diverse may refer to: Business *Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce *Diversity marketing, marketing communication targeting diverse customers * ...

and recognized the severity of global

biodiversity loss Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...

and degradation of ecosystems.

Drylands in East Africa

The East African drylands cover about 47% of land areas and are home to around 20 million people.

Pastoralists Pastoralism is a form of animal husbandry where domesticated animals (known as "livestock") are released onto large vegetated outdoor lands (pastures) for grazing, historically by nomadic people who moved around with their herds. The animal s ...

who rely on cattle for both economic and social well-being constitute the majority of rural

inhabitants Domicile is relevant to an individual's "personal law," which includes the law that governs a person's status and their property. It is independent of a person's nationality. Although a domicile may change from time to time, a person has only one ...

in the drylands. Pastoralists use strategic movement to gain access to pasture during the dry season using resources effectively However, due to a variety of factors, this method has changed and been constrained. Challenges connected to

demographics Demography () is the statistical study of populations, especially human beings. Demographic analysis examines and measures the dimensions and dynamics of populations; it can cover whole societies or groups defined by criteria such as ed ...

and climate change. Drylands occupy around 2 million km2 or respectively 90%, 75%, and 67% of Kenya, Tanzania, and Ethiopia respectively. The low level of precipitation and the high degree of variability limit the possibilities for rainfed crop production. More than 60 million people, or 40% of these countries’ population, live in drylands.

The 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

of dry and sub-humid lands allows them to adapt to the unpredictable rainfall patterns that lead to floods and droughts. These areas produce the vast amount the world's crops and

livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to ani ...

. Even further than producing the vast majority of crops in the world, it is also significant because it includes many different biomes.
Biomes include: *

Grassland A grassland is an area where the vegetation is dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...

* Savannahs *

Mediterranean climate A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...

Semi-arid lands

Semi-arid A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi- ...

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 The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...

, and several Southern countries in Asia.

Definition of semi-arid lands

According to literature, arid and semi-arid lands are defined based on the characteristics of the climate. For instance, Mongi et al. (2010) consider semi-arid lands as places where the annual rainfall ranges between 500 and 800mm. Fabricius et al. on the other hand also insist that the concept of aridity should also include conditions of aridity and semi-aridity. Furthermore, he considers that a huge part of the Sub-Saharan area covering around 40 countries on the continent is land having arid conditions. Arid and semi-arid lands have high evaporation for all required conditions high air temperature mainly during dry seasons, high and almost continuous isolation through the year, and the presence of dry gale-force winds. Inda Abba Hadera forest

Manifestations of Climate Change in semi-arid lands

Based on spatial repartition of

greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent material, such as glass, in which plants requiring regulated climatic conditions are grown.These ...

gas

emissions Emission may refer to: Chemical products * Emission of air pollutants, notably: **Flue gas, gas exiting to the atmosphere via a flue ** Exhaust gas, flue gas generated by fuel combustion ** Emission of greenhouse gases, which absorb and emit radi ...

(GGE) in the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...

, it seems that

contributes marginally in comparison to the rest of the world. Africa generates on average less than 4% of GGE produced in the world. Comparative data on GGE per person show that Europeans and Americans generate about 50 to 100 times more gas than Africans (Thiam, 2009). Based on the consequences caused by variability and climate change, it appears that African populations are more vulnerable than others. To illustrate, the trend of reduced rainfall in the Sahel area has been marked by climatic extremes with devastating consequences on natural resources, agricultural and pastoral activities, etc. In semi-arid lands, manifestations of climate change on communities and socio-economic activities are more diversified. The characterization and impact of the variability trend of rainfall depend on several random factors. Among the random factors, we can mention, the nature and the critical thresholds of extreme events, the frequency of these extremes according to regions, the precision of data used, and the results of mathematical simulations, and propagation. The state of scientific knowledge has allowed for the identification of the principal manifestations of climate change on the development of socio-economic activities in semi-arid lands. These manifestations are: * Increased variability of precipitations and their characteristics (number of rainfall days, date of start, length of the season) that can be translated to an abrupt alternative between dry and humid years. * a shorter rainy season correlatively to its late start; an increase in the occurrence of dry sequences that can happen at any time in space and time during the actual period; * a tendency to the increment of maximal rains cumulated in fewer consecutive days, that causes damage and important loss on socio-economic systems (culture, infrastructure) and humans; Dry and violent winds associated with very scarce rainfall that prevent enough humidification of the soils; making difficult the development of the whole vegetal life; * The actual rise without compromise of observed temperatures according to forecasts of the GIEC creates stressful thermal situations that may seriously handicap vegetal and animal productivity.

Adaptation, Resilience in SALS

In semi-arid lands where pastoralism is the principal activity, the main adaptation measures are an early departure to

transhumance Transhumance is a type of pastoralism or nomadism, a seasonal movement of livestock between fixed summer and winter pastures. In montane regions (''vertical transhumance''), it implies movement between higher pastures in summer and lower val ...

, the reduction of the size of the herd, a change in the management of water, and

diversification Diversification may refer to: Biology and agriculture * Genetic divergence, emergence of subpopulations that have accumulated independent genetic changes * Agricultural diversification involves the re-allocation of some of a farm's resources to n ...

of paths of transhumance. This allows

breeders A breeder is a person who selectively breeds carefully selected mates, normally of the same breed to sexually reproduce offspring with specific, consistently replicable qualities and characteristics. This might be as a farmer, agriculturalist, o ...

to safeguard their livestock and prevent huge losses as was the case in the

drought A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, an ...

of the seventies.

Breeders A breeder is a person who selectively breeds carefully selected mates, normally of the same breed to sexually reproduce offspring with specific, consistently replicable qualities and characteristics. This might be as a farmer, agriculturalist, o ...

purchase stock for the

or simply stock it. They become proactive (trade, real estate, guarding, transport) in certain countries like Burkina Faso, Senegal, Mali, and

Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...

. These adaptation strategies allow them to be more resilient to climate change
Brazilian semi-arid region

Arid lands.

Arid lands make up about 41% of the world's land and are home to 20% of the world's people. They have several characteristics that make them unique : # Rainfall scarcity # High temperatures #

Evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transp ...

Low humidity

Hyper-arid lands

These lands cover 4.2% of the world and consist of areas without vegetation. They receive irregular rainfall that barely surpasses 100 millimeters, and in some cases, they may not receive rainfall for several years.
Dry land - panoramio

References

{{Authority control Biomes