Added: 02/19/2006 |
Semiarid climates characterise regions with little precipitationClimate in a narrow sense is usually defined as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period is 30 years. These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.
Have you ever wondered why one area of the world is a desert, another a grassland, and another a rainforest? Why are there different forests and deserts, and why are there different types of life in each area? The answer is climate. Climate is the characteristic condition of the atmosphere near the earth's surface at a certain place on earth. It is the long-term weather of that area (at least 30 years). This includes the region's general pattern of weather conditions, seasons and weather extremes like hurricanes, droughts, or rainy periods. Two of the most important factors determining an area's climate are air temperature and precipitation.
World biomes are controlled by climate. The climate of a region will determine what plants will grow there, and what animals will inhabit it. All three components, climate, plants and animals are interwoven to create the fabric of a semiarid desert biome.
The climate of the temperate and tropical arid (including semiarid regions) zone is both an asset and a liability. Generally, dry, mild temperatures during the winter season offer a competitive advantage both to farmers and tourist hotel operators. However, the nature of rainfall is a distinct liability. Arid and semiarid climates are characterized by low precipitation amounts. An equally limiting feature of the arid climate is the high spatial and temporal variability of rainfall or, drought. High variability, rather than the low absolute rainfall amounts, introduces high elements of risk to most land use activities in arid regions. The economic, social and environmental cost of accommodating periodic drought determines the long-term viability of arid land uses.
Desert and semiarid climates occur in regions with little precipitation. Desert climates are drier than semiarid climates. Semiarid climates, also called steppe climates, usually border desert climates. In both climate groups, the temperature change between day and night is considerable. One reason for the wide swings in temperature is that the skies are clear and the air is dry. Clouds would reflect much of the sun's intense radiation during the day, slowing the rate of heating of the air near the surface. At night, clouds and water vapor would absorb much of the earth's radiation--most of which consists of infrared rays--slowing the rate of cooling.
Semiarid and desert climates occur over a greater land area than any other climate grouping. They occur in both tropical and middle latitudes. They cover broad east-west bands near 30 degrees north and south latitude.
Middle latitude semiarid and desert climates are in the rain shadows of mountain ranges. Winds that descend the leeward slopes of these ranges are warm and dry. Middle latitude semiarid areas and deserts differ from their tropical counterparts mainly in their seasonal temperature changes. Winters are much colder in middle latitude semiarid areas and deserts.
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