Wednesday, July 05, 2006
Er. Mohammad Ashraf Fazili (FIE, MIRC)
The World Environment Day theme selected for 2006 is Deserts and Desertification and the slogan is: Don’t Desert Dry lands, which emphasizes the importance of protecting dry lands, which cover more than 40 % of the planet’s surface. The ecosystem is home to one-third of the world’s people who are more vulnerable members of society. In the face of this situation, the UN General Assembly in it’s 58th session period decided on declaring 2006, the International Year of Deserts and Desertification (IYDD). This theme was chosen in order to draw attention to the need to reduce the rate of biodiversity loss in arid zones which result from human activities and consequently to prevent further land degradation. The IYDD provides higher visibility opportunity and importance to dry lands issues, covering 40 % of the planet’s land cover & sustains over 2000 million people, containing one of the most beautiful world ecosystems: the deserts. This year will also pay homage to the planet’s deserts heritage & fragile beauty with special emphasis over the global nature of the problem.
“Almost half of the land surface of the earth is drylands if we include grassland & all arid regions,” said Mr. Djoghlaf, Executive Secretary to the Convention on Biological Diversity. “One in six people depends on these fragile ecosystems for their survival,” said Mr. Djoghlaf. “These are the poorest of the poor & any further degradation of the biodiversity of drylands will lead to increased poverty. If implemented, the Convention’s programme of work on the biological diversity of dry sub-humid lands can encourage conservation & sustainable use of biological diversity in drylands,” he urged. “It is within our power to substantially reduce the rate of loss of biological diversity in Drylands by the year 2010 & make a substantial contribution to poverty reduction, for the sake of all life on earth”
Regions of the World:
The earth’s land surface can be split up into six major vegetation zones: Desert, Coniferous Forest, Temperate Forest, Tropical Forest, Grass Land, Tundra & Poles, Each zone has its own particular characteristics, determined by climate, topography & latitude. Nature Species are adapted to the conditions of each region.
Deserts are areas where evaporation exceeds rainfall. They occur over a wide range of latitudes, between 15 & 35 degrees on either side of equator. One third of the earth’s land surface is classified as desert or semidesert (semidesert supports scrubby vegetation). Deserts form where clouds are prevented from developing by barrier mountains, wind patterns or other factors. Barrier mountains force up air by the prevailing wind. Water vapour in the air condenses & falls as rain or snow, so when the air reaches the far side of the mountain it is dry. Some deserts such as the Gobi, are so far from the sea that moist air never reaches them. Deserts often have large temperature swings between day & night. The Sahara can reach 55 c by day & drop below freezing point at night. Not all deserts are hot by day. Cold deserts exist in North America to the west of Rocky Mountains, in Eastern Argentina & throughout Central Asia. Plants & animals are scarce or absent from deserts. Those that are present are adapted to arid conditions. Deserts are natural laboratories in which to study the interactions of wind & sometimes water on the arid surface of planets. They contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Because deserts are dry, they are ideal places for human artifacts & fossils to be preserved. Deserts are also fragile environments. The misuse of these lands is a serious & growing problem in parts of our world.
There are as many definitions of deserts & classification systems as there are deserts in the world. Most classifications rely on some combination of the number of days of rainfall, the total amount of annual rainfall, temperature, humidity, or other factors. In 1953, Peveril Meigs divided desert regions on Earth into three categories according to the amount of precipitation they received. In this now widely accepted system, extremely arid lands have at least 12 consecutive months without rainfall, arid lands have less than 250 mm. of annual rainfall, & semiarid lands have a mean annual precipitation of between 250 & 500 mm. Arid & extremely arid land are deserts, & semiarid grasslands generally are referred to as steppes.
Dry areas created by global circulation patterns contain most of the deserts on the Earth. The deserts of our world are not restricted by latitude, longitude, or elevation. They occur from areas close to the poles down to areas near the Equator. The People’s Republic of China has the highest desert, the Qaidam Depression that is 2,600 meters above sea level, & one of the lowest deserts, the Turpan Depression that is 150 meters below sea level. Deserts are not confined to Earth. The atmospheric circulation patterns of other terrestrial planets with gaseous envelopes also depend on the rotation of those planets, the tilts of their axes, their distances from the Sun,& the composition & density of their atmospheres. Except for the poles, the entire surface of Mars is a desert. Venus also may support deserts.
The World’s Largest Deserts:
Desert Location App.Area (Lac sq.kms.)
Sahara N. Africa 90
Australian Australia 38
Arabian SW Asia 13
Takla Makan China 12.45
Gobi Central Asia 10.40
Kalhari Southern Africa 5.20
Turkestan Central Asia 4.50
Namib SW Africa 3.10
Somali Somalia 3.10
Sonoran USA/Mexico 2.60
Thar India/Pakistan 2.60
Deserts are of the types: Trade wind, Mid latitude, Rain shadow, Coastal,Monsoon, Polar, Paleodeserts, Extraterrestrial. A worldwide inventory of deserts has been developed using images from the Landsat satellites & from space & aerial photography. It defines five basic types of dunes: crescentic, linear, star, dome,& parbolic.
Mineral Resources in Deserts:
Some mineral deposits are formed, improved, or preserved by geologic processes that occur in arid lands as a consequence of climate. Ground water leaches ore minerals & redeposits them in zones near the water table. This leaching process concentrates these minerals as ore that can be mined. Of the 15 major types of mineral deposits in the Western Hemisphere formed by action of ground water, 13 occur in deserts.
Water evaporating in closed basins precipitates minerals such as gypsum, salts ( including sodium nitrate & sodium chloride), & borates. Boron, from borax & borate evaporates, is an essential ingredient in the manufacture of glass, ceramics, enamel, agricultural chemicals, water softeners, & pharmaceuticals. Borates are mined from evaporate deposits at Searles Lake, California, & other desert locations. The total value of chemicals that have been produced from Searles Lake substantially exceeds $! Billion. The Atacama Desert of South America is unique among the deserts of the world in its great abundance of saline minerals. Sodium nitrate has been mined for explosives & fertilizer in the Atacama since the middle of the 19th. Century. Nearly 3 million tons were mined during World War 1.
Valuable minerals located in arid lands include copper in the USA, Chile, Peru, & Iran; iron & lead-zinc ore in Australia; chromite in Turkey, & gold, silver, & uranium deposits in Australia & the USA. Nonmetallic mineral resources & rocks such as beryllium, mica, lithium, clays, pumice, & scoria also occur in arid regions. Sodium carbonate, sulfate, borate, nitrate, lithium, bromine, iodine, calcium,& strontium compounds come from sediments near-surface brines formed by evaporation of inland bodies of water, often during geologically recent times .The Green Formation of Colorado, Wyoming, & Utah contains alluvial fan deposits & playa evaporates created in a huge lake whose level fluctuated for millions of years. Economically significant deposits of trona, a major source of sodium compounds, & thick layers of oil shale were created in the arid environment.
Some of the more productive petroleum areas on Earth are found in arid & semiarid regions of Africa & the Mideast, although the oil reservoirs were origionally formed in shallow marine environments. Recent climate change has placed these reservoirs in an arid environment. Other oil reservoirs, however, are presumed to be eolian in origin & are presently found in humid environments. The Rotliegendes, a hydrocarbon reservoir in the North Sea, is associated with extensive evaporate deposits. Many of the major US hydrocarbon resources may come from eolian sands. Ancient alluvial fan sequences may also be hydrocarbon reservoirs.