Drylands are defined by a scarcity of water. Drylands are zones whereprecipitation is balanced byevaporation from surfaces and bytranspiration by plants (evapotranspiration).[1] TheUnited Nations Environment Program defines drylands astropical andtemperate areas with anaridity index of less than 0.65.[2] Drylands can be classified into four sub-types:
Some authorities regard hyper-arid lands asdeserts (United Nations Convention to Combat Desertification) although a number of the world's deserts include both hyper-arid and arid climate zones. TheUNCCD excludes hyper-arid zones from its definition of drylands.
Drylands cover 41.3% of the Earth's land surface, including 15% ofLatin America, 66% ofAfrica, 40% ofAsia, and 24% ofEurope. There is a significantly greater proportion of drylands indeveloping countries (72%), and the proportion increases witharidity: almost 100% of all hyper-arid lands are in the developing world. Nevertheless, theUnited States,Australia, and several countries inSouthern Europe also contain significant dryland areas.[2]
Drylands are complex evolving structures, whose characteristics and dynamic properties depend on many interrelated interactions betweenclimate,soil, andvegetation.[3] Drylands are highly vulnerable to climate change.
The livelihoods of millions of people indeveloping countries depend highly on drylandbiodiversity 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.[4] Dryland inhabitants' lifestyle provides global environmental benefits which contribute to haltclimate change, such ascarbon sequestration and species conservation. Dryland biodiversity is equally of central importance as to ensuringsustainable development, along with providing significant global economic values through the provision ofecosystem services and biodiversity products. The UN Conference on Sustainable DevelopmentRio+20, held inBrazil in June 2012, stressed the intrinsic value ofbiologicaldiversity and recognized the severity of globalbiodiversity loss and degradation of ecosystems.[5]
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 andfood security.[6][7] Drylands ecosystems also feature climatetipping points.[8]
One fifth of drylands are already degraded, and this is expected to increase significantly asgreenhouse gas emissions rise.[9] 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. Most of these changes have transformed once-humid landscapes into drylands.[10]
Sustainable land management practices (such as mobilepastoralism), restoring degraded lands, andclimate-smart agriculture can mitigate these impacts.[9] Addressing urban expansion's indirect impacts on dryland habitats is also important for preserving biodiversity.[11]
The East African drylands cover about 47% of land areas and are home to around 20 million people.[citation needed]Pastoralists who rely on cattle for both economic and social well-being constitute the majority of ruralinhabitants in the drylands. Pastoralists use strategic movement to gain access to pasture during the dry season, using the available resources effectively. However, due to a variety of factors, this method has changed and been constrained. Challenges connected todemographics and climate change.[12] The greatest issue in drylands, is land degradation which poses a huge danger to the world's capacity to end hunger.[13] Drylands occupy around 2 million km² and 90% of Kenya,[14] 75% of Tanzania,[15] and 67% of Ethiopia. More than 60 million people, or 40% of these countries’ population, live in drylands. 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.[16]
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Countries like Burkina Faso, Botswana, Iraq, Kazakhstan, Turkmenistan and the Republic of Moldova, are 99% covered in areas of dry and sub-humid lands.[17] Thebiodiversity of dry and sub-humid lands allows them to adapt to the unpredictable rainfall patterns that lead to floods and droughts.[18] These areas produce the vast amount the world's crops andlivestock. 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 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 theequator, and several Southern countries in Asia.[19]
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.[20] Fabricius et al. on the other hand insist that the concept of aridity should also include conditions of aridity and semi-aridity.[21] Furthermore, they consider 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 much higher evapotranspiration rates as compared to the precipitation along with high air temperature mainly during dry seasons, high and almost continuous isolation throughout the year, and the presence of dry gale-force winds.[22]
Manifestations of climate change in semi-arid lands
Based on spatial repartition ofgreenhouse gas emissions (GGE) in theatmosphere, it seems thatAfrica contributes marginally in comparison to the rest of the world. Africa generates on average less than 4% ofgreenhouse gas emissions 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, African populations appear to be 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:[22]
Adaptation and resilience
In semi-arid lands where pastoralism is the principal activity, the main adaptation measures are an early departure totranshumance, the reduction of the size of the herd, a change in the management of water, and diversification of paths of transhumance.[23] This allowsbreeders to safeguard their livestock and prevent huge losses as was the case in thedrought of the seventies.Breeders purchase stock for thelivestock or simply stock it. They become proactive (engage in trade, real estate, guarding, transport) in certain countries like Burkina Faso, Senegal, Mali, andKenya.[23][24] These adaptation strategies allow them to be more resilient to the socio-economic consequences of climate change.
Arid lands make up about 41% of the world's land and are home to 20% of the world's people.[25] They have several characteristics that make them unique :
These lands cover 4.2% of the world[26] and consist of areas without vegetation. They receive irregular rainfall that barely surpasses 100 mm, and in some cases, they may not receive rainfall for several years.
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