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Arid lands are characterized by low rainfall and high evapotranspiration. Depending on definition, they are also referred to as drylands, or alternatively, as one category within drylands. For this purpose, arid lands are described in their broader definition as drylands. Drylands encompass arid, semi-arid, and sub-humid zones where average annual rainfall is lower than total evapotranspiration (classified using the aridity index). Drylands generally exclude true deserts, such as the Sahara, which are considered hyper-arid and are of low productive potential and consequently low population density. Drylands cover 41 percent of the earth’s land surface and support more than one-third of its population. Every continent contains drylands that often cover extensive areas. However, they are most extensive in Africa and Asia. Australia, the United States, Russia, and China have large dryland areas. Other countries, such as Botswana, Burkina Faso, Turkmenistan, and Iraq, however, have nearly all of their area classified as drylands. Some of the commonly known drylands include the Sahel (Africa), the Australian Outback, Patagonia (South America), and the Great Plains (North America).
Environment and Population
Popular misconceptions conceive drylands as empty spaces that are barren and unproductive. In reality, drylands are complex ecosystems with unique biodiversity and environmental goods and services that provide a basis of living for millions of people. Drylands cover a range of ecosystems that are highly heterogeneous in their topography, climate, geology, and biodiversity. Drylands are comprised of deserts (except hyper-arid deserts), grasslands, savannas, shrublands and woodlands, agricultural lands, and urban areas. Plants and animals have to cope with scarce water supplies due to low annual rainfall, high variability, and high temperatures. Most species have adapted to the conditions, such as plants that have deep and extensive root systems and photosynthesize at night, and animals that stay inactive during the day. The lack of reliable rainfall makes other water sources, such as groundwater, streams, and dew, even more important.
Drylands are generally exposed to climate regimes that are not favorable for crop production, as rainfall patterns are unpredictable. Nonetheless, more than two billion people live in drylands, mainly in developing countries. Here, populations are among the poorest in the world. Particularly in Africa, South America, and Asia, inhabitants are heavily dependent on dryland resources to meet their basic needs. Drylands lag far behind in economy, infrastructure, well-being, and development terms. For instance, infant mortality in drylands in developing countries is twice as high as in nondryland areas, and 10 times higher than in developed countries. Moreover, access to clean drinking water and adequate sanitation is inadequate and leads to poor health conditions.
Although drylands are considered marginal for agriculture due to limited water resources, they currently account for more than 40 percent of the global cultivated area. Communities make a living as small-scale farmers or livestock herders and rely on drylands for wood fuel, construction materials, and medicinal plants. However, people are highly vulnerable to periodic droughts and are affected by food insecurity. While the majority of populations live in rural areas, large cities are located in drylands, such as Cairo, Mexico City, Teheran, Cape Town, and Las Vegas. Drylands have supported people’s livelihoods for thousands of years. Their communities are highly resilient and have developed sustainable lifestyles and systems allowing them to survive in these harsh conditions and manage limited natural resources. Drylands are also the origin of important food grains (such as wheat, sorghum, barley, and millet).
Challenges and Opportunities
Over time, there have been misunderstandings surrounding drylands and the human impact on these systems. One of the most controversial debates concerns that of land degradation and desertification. During the early 20th century, scientists started raising concern about degradation, blaming vegetation change on overgrazing, deforestation, and unsustainable land management. Global estimates on land degradation in drylands vary considerably anywhere from 20 to 70 percent. The coexistence of high levels of poverty and food insecurity with high rates of land degradation in drylands has led to the understanding that these factors are closely related. This relationship can best be described as a downward spiral of poverty and degradation, where resource-poor farmers place increased pressure on the land, while degradation affects land productivity, leading to a decline in crop yields and contributes to food insecurity. In recent years, however, evidence suggests that the relationship between poverty and land degradation is not always that causal, but highly dependent on local conditions. It is also understood that climate plays a more prominent role than previously assumed.
Living in the Drylands
Drylands have some of the highest population growth rates in the world. This is not only true in developing countries, but also in the developed world. States in the southwestern United States, such as Nevada and Arizona, have some of the fastest growing populations in the country due to substantial in-migration. Within the context of high growth rates, urban areas are rapidly expanding, and growing demands for food and water have significant impacts on dryland environments. Growing populations are placing increasing pressure on available resources, which may result in the extension of cultivation into more marginal areas. Resource conflicts are increasing and destabilizing people’s ability to cope with natural disasters. Land degradation, in combination with increasing populations, may trigger severe food crises in the future. These processes are anticipated to worsen over the next decades, as population growth is likely to exacerbate resource scarcity problems. Continuing oil development and ambitious water developments are anticipated to significantly impact drylands. Moreover, forecasts predict significant impacts of climate change in drylands, where drier and hotter climates are expected. This may affect agricultural potential and food security.
Drylands will continue to supply a range of goods and services and possess comparative advantages that may provide opportunities in the future. If water supplies can be stabilized, drylands provide good conditions for food and forage production. Wild varieties of major food crops are sources of plant genetic materials for developing droughtresistant crops. The potential for alternative energy production is high, through solar and wind power. Unique landscapes and biodiversity attract tourism. There is also the potential for drylands to act as carbon sinks to mitigate climate change.
Considering their economic importance, geographic extent, environmental diversity, and human welfare, drylands should be placed high on political agendas. Historically, this was rarely the case, due to their remoteness and the perception that drylands are simple ecosystems of little economic value. With population growth, dwindling resources, and climate change, food insecurity in drylands is likely to worsen. The challenge faced by the international community is to sustain growing populations in drylands, while alleviating poverty and safeguarding the environment.
The reduction of poverty in drylands needs to become a priority, particularly within the context of international development efforts (such as the Uited Nations [UN] Millennium Development Goals). The UN declared 2006 the International Year of Deserts and Desertification, creating a platform for discussion and research.
- P. Beaumont, Drylands: Environmental Management and Development (Routledge, 1989);
- Hutchinson, S. Herrmann, and W. Foerch, The Future of Drylands-Revisited: A Review of Fifty Years of Drylands Research (United Nations Educational, Scientific and Cultural Organization, in press);
- Leach and R. Mearns, The Lie of the Land: Challenging Received Wisdom on the African Environment (International African Institute, 1996);
- Mortimore, Roots in the African Dust: Sustaining the Drylands (Cambridge University Press, 1998);
- Warren, Y.C. Sud, and B. Rozanov, “The Future of Deserts,” Journal of Arid Environments (v.32, 1996);
- P. White and J. Nackoney, Drylands, People, and Ecosystem Goods and Services: A Web-Based Geospatial Analysis (World Resources Institute, 2003);
- R.P. White, D. Tunstall, and N. Henninger, An Ecosystem Approach to Drylands: Building Support for New Development Information Policy Brief (World Resources Institute, 2002).