18. Dryland Systems: It's about Water

IUCN considers drylands as tropical and temperate landscapes and regions with an aridity index value of less than 0.65, which includes the following dryland sub-types: dry sub-humid, semi-arid, arid, and hyperarid (deserts) (IUCN, 2008b). Such drylands constitute approximately 40% of the terrestrial surface of the planet, and can be found in both developing and developed countries. At least 30% of the world's cultivated plants originated in drylands, and drylands are home to 47% of endemic bird areas and 26% of protected areas worldwide.

IUCN has an inclusive approach to mosaic where temperature rather than water availability dryland landscapes, and so includes urban limits biological productivity. In addition, IUCN and wetland areas within dryland regions and also includes seasonal drylands in the scope of its landscapes. However, for the purposes of IUCN's drylands work, specifically grasslands where their programmes of work on drylands, Arctic and range and species composition are determined by Antarctic dry areas are excluded, as these are areas water scarcity.

Figure 18.1 Distribution of the world's drylands (MA, 2005a)

Biodiversity in drylands is well adapted to harsh conditions and drylands are significant locations for endemism around the world. Species' adaptive strategies range from the architectural wonder of termite mounds which insulate the colonies from extreme temperatures to the desert amphibians which burrow into the sand and remain dormant until rains come. Indeed, some of these strategies have been the source of important discoveries in support of improving human livelihoods. Nevertheless, with changing climate and increasing human demands on these dryland systems, the special biodiversity living here is under increasing threat.

Drylands are home to some of the most charismatic species, support high species endemism and comprise many unique ecosystems and biomes, including Mediterranean-type ecosystems, grasslands, savannahs, dry forest, coastal areas, deserts, fynbos and the succulent Karoo (the latter two being highly distinctive vegetation types unique to southern Africa) (Zeidler and Mulongoy, 2003; White et al., 2000; Bonkoungou and Niamir-Fuller, 2001). Furthermore, many other ecosystems, such as riparian or forest ecosystems are located within the drylands landscapes and are at risk from drylands degradation.

Functioning dryland ecosystems provide many ecosystem services including crops for food and medicines, forage for animals, genetic resources, water for both people and animals, and materials for housing and clothing. In addition, they can be important sources of income (e.g. tourism) or cultural and spiritual support. The potential value of some of these services can be expressed in terms of percentage of agricultural output in countries that are largely dryland. For example, agriculture accounts for more than 30% of GDP in Afghanistan, Kenya and Sudan. The dryland portions of India contribute 45% of the country's agricultural output. Chinese drylands are home to 78 million cashmere goats that supply 65–75% of the global market, and Mongolia generates 30% of GDP from dryland pastoralism.

Pastoralism, which is usually most profitable on lands marginal for crops, is an important source of livelihoods in drylands. Mobile herding allows better use of grazing land that is subject to variations in rainfall and temperature. Crop farming or sedentary herds of livestock do not have the flexibility to move when conditions are no longer suitable. However, some traditional practices support crop farming through tree planting and other mechanisms to support natural regeneration.

Dryland-adapted species tend to be ecologically resilient and able to cope with extremes of environment. Nevertheless, according to the Millennium Ecosystem Assessment (MA), 10–20% of drylands are being degraded, threatening billions of hectares of rangelands and croplands with subsequent impacts on the more than 2 billion people living in these ecosystems (2000 data).


Desertification is increasingly a topic of discussion beyond its “homeland” venue of the United Nations Convention to Combat Desertification (UNCCD). While desertification is an important issue for drylands, most drylands are not desertified. Desertification has been defined, through the UNCCD, as “land degradation in arid, semi-arid, and dry sub-humid lands”. In turn, that degradation is expressed as a persistent reduction of biological and economic productivity and can be measured by monitoring outputs of ecosystem services including crops and water supplies.

The causes of desertification include:

Desertification occurs on all continents except Antarctica and has particular impacts on the poor in drylands where they depend heavily on the ecosystem services that these systems provide.

While many impacts of desertification on drylands are local, there are also regional and global consequences. From an environmental perspective, loss of vegetation leads to soil loss, erosion, and downstream flooding. From the social perspective, people living in degraded drylands may be forced to migrate to other areas that are already crowded and unable to cope with increasing demands.

Other impacts of dryland degradation on associated lifestyles include:


The loss of biodiversity, critically important in these challenging environments, is felt particularly keenly by dryland inhabitants. Dryland biodiversity, though, provides support not only for local inhabitants but is also the source of many services for wealthier parts of the world. Consider medicinal plants such as Harpagophytum sp., or Hoodia sp. used to treat common “Western” ailments such as arthritis and obesity. Without sound dryland management, solutions to today's and tomorrow's health problems could disappear before we discover them (Box 18.1).


Desertification is being driven by a suite of factors including water scarcity, intensive use of ecosystem services, and climate change. These factors are strongly linked as climate change will likely result in increasing water scarcity in many drylands with resulting decreases in services in spite of increasing demand. Such changes also tend to increase the risks of conflict.

Intensive use of ecosystem services, especially water

Continuing population growth and the consequent increase in food demand is likely to increase pressure to make land available for cultivation and could result in further degradation and conflict among ethnic groups. Dryland regions undergo cyclical episodes of water scarcity during which local people are more vulnerable to its effects, namely food shortages and health crises from lack of water.

Climate change

Climate change impacts present a complex picture of possibilities for drylands. For some, more intense and extended drought could eliminate any productivity from a dryland landscape. For others, significant increases in precipitation (and in intensity in volume and temporal distribution) could transform drylands into more humid systems. This could potentially be beneficial but may also lead to conflicts between farmers and pastoralists.

Desertification contributes to climate change through soil and vegetation loss which decrease the land's carbon storage capacity. An estimated 300 million tonnes of carbon are lost to the atmosphere from drylands as a result of desertification each year (about 4% of the total global emissions from all sources combined) (MA, 2005a).

Box 18.1 Gum Arabic – a case study in drylands ecosystem services

Gum Arabic in Sudan drylands

The most important forest type in the Sudan may be the gum Arabic belt, which lies within the low-rain savannah zone. Ecosystem services provided by the hashab trees (Acacia Senegal) in this belt include:

o Acting as a natural barrier to protect more than 40% of the total area of Sudan from desert encroachment.

o Supporting family economies through provision of gum Arabic from hashab trees, a multipurpose tree that has an
   important role in generating income, and meeting household wood energy and fodder demands.

o Enriching the soil fertility, possibly also through biological nitrogen fixation.

In pharaonic times, gum Arabic was also used for body mummification and making watercolours, dyes and paint.

Typically, land use in Sudan included a bush-fallow system that supported both crop cultivation and harvest of gum Arabic, The bush fallow cycle starts with the clearing of an old gum garden (15–20 years old) for the cultivation of agricultural crops. Trees are cut at 10cm from ground level, and stumps are left to initiate vigorous coppice re-growth while the cleared area is cultivated for a period of 4–6 years. When soil fertility declines, crop growing ceases and the area is left fallow save for the remaining trees which are tapped for gum Arabic until the age of 15–20 years. The cycle can then be repeated. This approach was recognized and considered one of the most successful forms of natural forest management in the tropical drylands and regarded as sustainable in terms of its environmental, social and economic benefits.

Today's challenges to gum Arabic production in Sudan's drylands

The importance of gum Arabic in the livelihoods of the people inhabiting the gum belt is well known. More than four million people in the gum belt of Sudan are involved in gum tapping, harvesting, cleaning and trading of gum. Sudan commands 70–80% of the world gum Arabic market. Its annual exports range from 20,000–50,000 metric tonnes with an annual average for the past decade of 25,000 metric tonnes.

In recent decades, the bush fallow system has been disrupted and the traditional rotational bush-fallow cultivation cycle has been dramatically shortened or completely abandoned with consequent impacts on both crop and gum Arabic production. Sustainable management of the gum gardens is threatened because of severe droughts and indiscriminate clearing of A. senegal stands for firewood and charcoal production. In addition to these threats, gum production communities suffer from the lack of regulatory infrastructure as well as lack of market information upon which to plan distribution and sales of any gum produced. Other challenges include lack of finance and transportation facilities. As a result, one report has noted that the actual return to gum producers does not exceed 40% of the production cost. To try to address these issues, Gum Producers' Associations (GPAs) were formed in several provinces as a test case and then expanded. Today 1,650 GPAs have two million members of which 30% are women.

Source: A.G. Mohammed, 2008


Increased knowledge

One of the most important efforts needed is increased understanding of drylands, factors involved and resulting vulnerability of local people. Decision makers and technicians charged with conservation and devising livelihood alternatives need appropriate knowledge on the potentials, limitations and ecological opportunities presented by arid and semi-arid lands and a better understanding of urban and external impacts on arid and semi-arid lands. In response, the Food and Agriculture Organization (FAO), along with many partners, has developed the Land Degradation Assessment of Drylands that includes mapping, indicators and country-level pilot studies to help increase our knowledge of drylands. The UNCCD and the World Meteorological Organization (WMO) are collaborating on a project to help with prevention, warning and monitoring of drought.

The value of drylands and dryland services also needs to be better understood. To date, drylands have been characterized by under-investment as potential opportunities are overlooked in favour of agricultural lands, tropical forests or marine ecosystems.


Water resource management

Integrated water resource management is a key means by which to prevent desertification by ensuring that land management policies are adapted to local traditions and needs. Such policies should support existing pastoralist lifestyles and maintenance of the traditional knowledge, avoiding unnecessary transition to more water-intensive cultivation. Dryland management involves water management and requires inter-sectoral cooperation to be effective. Reducing stress on dryland areas may sometimes require development and promotion of alternative livelihoods, including livelihoods in nearby non-dryland areas.

Restoration of degraded drylands

As with other degraded ecosystems, dryland restoration should be undertaken at a landscape scale, utilizing the principles of ecosystem approaches.

Drylands policy and governance

Dogmatic definitions of what a dryland is are not helpful in policy terms. In fact, the definition of drylands in the UNCCD differs from that in the Convention on Biological Diversity (CBD) with the former being more precise in terms of precipitation levels and the latter including a larger area through inclusion of specific vegetation types (Box 14.1). The result is a potential challenge for parties trying to implement drylands programmes of work in both conventions and this is a typical issue that underpins the need for harmonization across multilateral environmental agreements (MEAs).

However, no matter what the definition, the governance issues facing drylands management remain the same, namely:

As highlighted in earlier chapters, these governance issues will also need to bring in concerns relating to climate change (Chapter 5) and poverty reduction (Chapter 1).

Drylands are productive ecosystems supporting large numbers of people but these people are vulnerable to changing climates, markets and rights (Mortimore et al., 2008). Effectively managing drylands – and thereby preventing desertification – will be a major step towards poverty reduction and biodiversity conservation in a significant portion of our world.

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