SciDev.Net
Science and Development Network
News, views and information about science, technology and the developing world
Definitions
List of terms for Desert science
Producing enough food for a rapidly growing population, and taking care of our planet are two of the world's biggest challenges.
D
Desertification
Twelve million hectares of land is being taken out of cultivation every year. The UN Convention to Combat Desertification defines desertification as "land degradation in arid, semi-arid and dry sub-humid areas" brought about by climate change and human activities, such as overgrazing and deforestation. This is not the only definition, however, and desertification is not regarded as being irreversible.
In most cases desertification involves a decline in land productivity, and not advancing desert sands. Land degradation often affects the poorest and most vulnerable in society. An estimated 250 million, for example, have had to leave their homes because soils are longer suitable for cultivation.
Deserts
Deserts are regions of the world that receive large amounts of sunshine, but very little rainfall, making the land unsuitable to grow crops. Strong winds and high temperatures remove moisture through evaporation. Average desert rainfall is less than 250 millimetres per year. Parts of the Sahara and Atacama deserts receive much less – around 1 millimetre per year. Often, the heat turns the rainfall into vapour, which returns to the atmosphere before it has a chance of reaching the ground.
The Sahara is the largest desert in the northern hemisphere. Asia’s great deserts include the Thar in India and Pakistan and the Gobi in China. In the US, deserts are found in the states of Arizona, California, Nevada and New Mexico. In Africa south of the Sahara, deserts are in Botswana, Namibia and South Africa.
Drought
When a region receives less than its normal or predicted amount of water. Drought is caused by decreased rainfall, increased evaporation because of higher temperatures, or a combination of these two processes. In some countries a drought is declared after a minimum number of consecutive days without rain.
Drylands
Drylands are on the margins of deserts and contain land that can be suitable for agriculture if irrigated. Drylands in the Middle East and North Africa, for example, are often the original homes for many of the world’s most important food crops such as wheat, barley, millet and sorghum.
Dunes
Dunes are the large accumulations of sand that can form shapes such as hills, or ridges in a desert landscape. Half of all dunes are parallel ridges of sand that can extend for 20 kilometres or more.
Information Services
The global food crisis
A series of articles debate key issues such as GM technology, media reporting and agricultural policymaking
