Deserts and xeric shrublands are a biome defined by the World Wide Fund for Nature . Deserts and xeric ( Ancient Greek ξηρός xērós 'dry') shrublands form the largest terrestrial biome, covering 19% of Earth 's land surface area. Ecoregions in this habitat type vary greatly in the amount of annual rainfall they receive, usually less than 250 millimetres (10 in) annually except in the margins. Generally evaporation exceeds rainfall in these ecoregions. Temperature variability is also diverse in these lands. Many deserts, such as the Sahara , are hot year-round, but others, such as East Asia's Gobi Desert , become quite cold during the winter.
6-632: Nama Karoo is a xeric shrubland ecoregion located on the central plateau of South Africa and Namibia . It occupies most of the interior of the western half of South Africa and extends into the southern interior of Namibia. The climate of the Nama Karoo tends to be volatile, unpredictable and rather harsh, with only the most specially-adapted organisms calling the region home. The annual ‘dry’ season—a time of blistering hot weather and drought —is long, often taking place over autumn and winter, and into early spring. Heavy rainfall primarily occurs in
12-441: A rich array of habitats. Many of these habitats are ephemeral in nature, reflecting the paucity and seasonality of available water. Woody-stemmed shrubs and plants characterize vegetation in these regions. Above all, these plants have evolved to minimize water loss. Animal biodiversity is equally well adapted and quite diverse. The conversion of productive drylands to desert conditions, known as desertification , can occur from
18-482: A variety of causes. One is human intervention, including intensive agricultural tillage or overgrazing in areas that cannot support such exploitation. Climatic shifts such as global warming or the Milankovitch cycle (which drives glacials and interglacials ) also affect the pattern of deserts on Earth. Xeric shrublands can experience woody plant encroachment, which is the thickening of bushes and shrubs at
24-440: The expense of grasses. This process is often caused by unsustainable land management practices, such as overgrazing and fire suppression, but can also be a consequence of climate change . As a result, the shrublands' core ecosystem services are affected, including its biodiversity, productivity, and groundwater recharge. Woody plant encroachment can be an expression of land degradation. The World Wide Fund for Nature highlights
30-402: The mid-summer (January) exceeds 30 °C (86 °F), while mean minimum mid-winter (July) temperatures are below freezing. Xeric shrubland Temperature extremes are a characteristic of most deserts. High daytime temperatures give way to cold nights because there is no insulation provided by humidity and cloud cover. The diversity of climatic conditions, though quite harsh, supports
36-637: The spring and summer ‘wet’ season. This time of plenty can also vary, with total measured rainfall fluctuating between 100 and 520 millimetres (3.94 and 20.47 in) per year. Rainfall is also known to be highly seasonal, peaking between December and March. Precipitation tends to decrease from the east to west, and from north to south. As the climate changes, inter-annual rainfall trends become varied, and unpredictability comes to be expected, especially with increasingly prolonged periods of aridity . Temperature variations as large as 25 °C or 45 °F between day and night are common. Mean maximum temperatures in
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