What are Drylands?

Drylands conventionally are defined in terms of water stress, as terrestrial areas where the mean annual rainfall (including snow, fog, hail, etc) is lower than the total amount of water evaporated to the atmosphere. This definition usually excludes the polar regions and high mountain areas, which on account of their low average rainfall can be classified as drylands too. Drylands can be found on every continent and cover extensive areas of land – they stretch over 41% of Earth’s land surface.

Classification

Drylands are classified according to their climate using the Aridity Index. The Aridity Index is the ratio between precipitation (water, hail, snow, fog, etc.) to potential evapotranspiration (transpiration from plant and soil surface). Based on this index drylands are classified as hyper-arid, arid, semi-arid or dry sub-humid.


The importance of drylands to combat poverty and to achieve the MDGs

Drylands play an important role for human livelihoods, as the Millennium Ecosystem Assessment points out:

		More than 2 billion people live in drylands, most of them in developing countries.
		About 44% of all cultivated land area lies within drylands.
		Dryland population suffer from the poorest economic conditions worldwide.
		The infant mortality rate (about 54 per 1,000) for all dryland developing countries exceeds that from non-dryland countries by 23% or more.
		Scarcitiy of water limits access to clean drinking water and adequate sanitation, leading to poor health.

Thus, poverty reduction in dryland areas will be vital to achieve the MDGs. Resilient dryland ecosystems with their biological diversity are fundamental to the livelihoods of the people inhabiting drylands worldwide: Dryland people depend on their livestock that lives on grass and other vegetation, for food and social well-being. In addition, crop production, fuelwood and thatching material as well as many traditional medicines are obtained from wild and cultivated plants.

These ecosystem services are in decline as land is being degraded mainly because of population growth, unsustainable human activities and climate change. This in consequence deteriorates the already harsh conditions for the people living in drylands.

However, it is important to acknowledge that people living in drylands are remarkably resilient and have succeeded in inventing sustainable and flexible lifestyles that permit them to cover with some of the most severe natural calamities. Moreover, drylands people have succeeded in having sustainable lifestyles and management practices (as for example nomadic pastoralism) that maintain the delivery of dryland ecosystem services.

In this context it will be vital to acknowledge the knowledge and expertise of drylands people and to recognize the importance of sustainable drylands management to combat poverty.


Biodiversity of drylands

Drylands encompass a wide range of natural habitats, including deserts, grasslands and savannahs. The species diversity in drylands, except for arthropods, their predators and for example annual plants, is comparable low and declines with increasing aridity. Low primary production reduces especially the number of animals at higher trophic levels, thus naturally affecting the biotic interactions with desert ecosystems and thus their species diversity.

However, the biodiversity of drylands is unique with its remarkable adaptations of their fauna and flora to the extreme climatic and physical conditions. This often includes abilities to store water and features to reduce the loss of water as well as long periods of dormancy interrupted with short periods of high activity. Importantly, many major food crops, such as wheat, maize or sorghum, originated in dryland ecosystems.

In addition, drylands play a major role in global biophysical processes by reflecting and absorbing solar radiation, maintaining a balance of atmospheric constituents, and sustaining biodiversity and biomass.

Notwithstanding the conservation importance and the heightened risk rural people face in these areas, drylands receive less conservation support and rural development assistance than other biomes and centres of high biodiversity.