geographical position
The Sahara desert is bordered by the Atlantic Ocean in the west, the Red Sea in the east, the Mediterranean Sea in the north and the Sahel prairie in the south. This vast desert spans 1 1 countries: Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan and Tunisia.
In fact, the Sahara desert is not just a desert in the traditional sense. It has a variety of landforms, but the most famous is the sand dunes that often appear in movies. These dunes can reach nearly 600 feet (183 meters) high, but they only cover 15% of the whole desert. Other topographical features include mountains, plateaus, gravel-covered plains, salt flats, basins and depressions. An extinct volcano in Chad, Mount Kushi, is the highest point in the Sahara Desert, with an altitude of 1 1.204 ft (3415m); Katara depression is the lowest point in Salaha, with an altitude of 436 feet (133 meters).
Although the water resources in the whole region are very scarce, the Sahara has two permanent rivers (Nile and Niger), at least 20 seasonal lakes and huge aquifers, which are the main water sources of more than 90 major desert oases. At one time, the water resources management department was worried that the aquifer in the Sahara desert would be rapidly exhausted due to overuse, but a study published in Geophysical Research Letters in 20 13 found that the "fossil" (non-renewable) aquifer was still replenishing water through rainwater and runoff.
Animals and plants
Although the desert is harsh and dry, some plants and animals still make it their home.
According to the World Wildlife Fund, there are about 500 species of plants, 70 species of known mammals, 90 species of birds and 65,438+000 species of reptiles in the Sahara desert, as well as several kinds of spiders, scorpions and other small arthropods.
Camel is one of the most representative animals in the Sahara desert. According to a study in the Journal of Agricultural and Environmental Management Research 20 15, these large mammals originated in North America and finally crossed the Bering Isthmus 3 to 5 million years ago. About 3000 years ago, camels in the southeast of Arabian Peninsula were domesticated and used for desert transportation.
Camels, also known as "ships in the desert", can adapt well to the hot and dry environment. The hump on the hump stores fat, which can be used to supplement energy and water between meals. Camels store energy so efficiently that they can eat for months without drinking water for more than a week.
Other inhabitants of the Sahara desert include all kinds of gazelles, Adax (an antelope), cheetahs, wild cats, desert foxes and wild dogs. Many reptiles can also thrive in desert environment, including some kinds of snakes, lizards and even crocodiles. Some arthropods also live in the Sahara desert, such as dung beetles, scarabs, "death stalkers" scorpions and many kinds of ants.
The plants in the Sahara desert have adapted to the arid environment. Their roots go deep underground to find buried water, and their leaves are made into thorns to minimize water loss. There are no plants in the driest part of the desert, but in oasis areas, such as the Nile valley, there are all kinds of plants, including olive trees, date palms and various shrubs and grasses.
climate
According to a study published in Science Progress in 20 19, the Sahara desert will change from a dry and uninhabitable desert to a lush oasis every 20,000 years.
The author of this study studied the marine sediments containing dust deposits in the Sahara desert in the past 240 thousand years. The research team found that the cycle between the dry Sahara and the green Sahara corresponds to a slight change in the inclination of the earth's axis, which is also the driving factor of monsoon activity.
When the earth's axis tilts the northern hemisphere to the sun for one degree (about 24.5 degrees instead of 23.5 degrees today), it receives more sunlight and increases monsoon rainfall, thus supporting the lush green landscape of the Sahara desert.
Archaeologists have discovered prehistoric caves, rock paintings and other archaeological remains, providing clues for understanding the living conditions of the once green Sahara desert. Pottery fragments show that about 7000 years ago, ancient herders raised livestock and harvested plants in the now arid desert.
In the past 2000 years or so, the climate in the Sahara has been quite stable. The northeast wind dries the air over the desert and blows hot air to the equator. These winds can reach abnormal speeds and cause severe sandstorms, reducing local visibility to zero. The dust in the Sahara desert drifted all the way to the other side of the earth through the trade winds.
The precipitation in the Sahara desert varies from 0 to 3 inches every year, and it doesn't rain in some places for several years. Occasionally, it snows at high altitude. In summer, the temperature usually exceeds 100 degrees Fahrenheit (38 degrees Celsius) during the day and drops to near freezing point at night.
Impact of climate change
A study published in Climate magazine in 20 18 shows that the area of Sahara desert has increased by nearly 10% since 1920.
Although all deserts, including the Sahara desert, will become bigger in the dry season and smaller in the rainy season, human-induced climate change, coupled with the natural climate cycle, will make the Sahara desert bigger and smaller. The authors of this study estimate that about one third of desert expansion is caused by man-made climate change.
One proposal to mitigate the impact of climate change is to install large-scale wind and solar power plants in the Sahara region.
20 18 a study published in the journal science shows that these farms will provide clean energy, reduce the amount of greenhouse gases entering the atmosphere, and may also promote the increase of precipitation in nearby areas.
Computer simulation shows that in areas with wind farms, because wind turbines bring warm air from the upper atmosphere to the ground, there will be higher temperatures, especially at night. The researchers also estimate that the average rainfall of wind farms will double, thus increasing the vegetation by about 20%.
The simulation of solar power plants produced similar results.
The author predicts that a large Sahara wind farm will generate about 3 terawatts of electricity, while a large Sahara solar farm will generate about 79 terawatts of electricity, which greatly exceeds the electricity consumption of 65,438+08 terawatts in 2065,438+07. The extra energy can be used for larger-scale projects, including increasing agriculture and desalination.
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