The model builders took a vegetation distribution corresponding to what the fossil record suggests prevailed during the Green Sahara, and to their model they added the lower albedo, the greater roughness and the transpiration of water from the leaves of all this vegetation, flic result was an even moistcr climate: in the model the vegetation helps to set off convection in the atmosphere , pulling in the monsoon more strongly. Moreover, the vegetation across the Sahara recycles the rain that falls, allowing the monsoon to keep going strong as it travels farther up through North Africa.
The model forecasts enough rainfall to sustain the abundant vegetation that we know prevailed at that time; so, the loose ends are tied up to make a loop. The vegetation made the climate moister; and bccause the climate was moister, that specific type of vegetation could live there.
What the vegetation did was intensify a moist climate that would have existed to some extent anyway, because of the basic underpinning of increased summer sunlight. So, the feedback loop that made the climate "optimum" in the Sahara went something like this:.
The modern, weaker "green" note the lower case Sahara would be unstable, liable to end at any time given a slight push from the weather. But the models show that the ancient "Green" Sahara was far more stable, held in place by the stronger summer sunlight of the time. The only reason it ended was that the summer sunlight over the Sahara declined, to the point where the monsoon rains flickered and then died.
The final phase of drying of the ancient Sahara around 4. This rapid loss of rainfall is indicated by various forms of evidence that can be precisely dated from lake muds and other sediments. Despite any temporary reversals that may have happened, the overall shift from a lush green landscape to bare sand and rock was completed in at most a few centuries.
Yet, during this time there was a slow gradual decline in summer sunlight, taking several thousand years.
Since summer sunlight is really the underpinning cause of the Green Sahara, one might cxpect a similar gentle change in the climate of the Sahara during this period, and yet in fact it flipped relatively suddenly. The rapid end to the Green Sahara can only be explained by the way in which the vegetation system responds with its positive feedbacks. Sometimes positive feedbacks can help to stabilize a certain state, and this is what they did during a couple of thousand years between about 7, and 5, years ago when the summer sunlight was stronger, even though the sunlight was declining.
But positive feedbacks also tend to reach a sudden breaking point, beyond which they push things in completely the opposite direction. Instead of slamming rainfall up against the top of the scale, they slammed it down against the bottom of the scale.
The Sahara reached a point where the vegetation cover could no longer maintain the monsoon rains, even with its darker surface, its roughness and its abundant evaporative leaf area. The sunlight intensity could not quite ensure enough atmospheric upwelling, or enough evaporation, and the rains began to fail.
It is used frequently in making water wheels, water wells and also agricultural tools. These trees are beautiful and shady, so they are cultivated on wide road sides. Sycamore is an ever green large tree. Its height reaches 20 meters, when it is fully grown. Its branches spread horizontally over a diameter ranging meters, therefore it is planted in meters spacing. The fruit is carried on special branches that come from green branches. Flowers appear in sycamore when the age of the tree is ranging from 5 to 6 years old.
Sycamore fruit is like fig in form and structure. There are three main seasons for sycamore: the first season in the beginning of April, the second in the beginning of May and the third in the beginning of June. The fruit continues meagerly, especially in winter and autumn. An operation is usually run for fruits called circumcision in the early morning or afternoon when the age of the fruit ranges for 20 to They make splits in the tops of fruit whose diameter extends from 1.
Hatshepsut is generally regarded by historians as one of the most successful pharaohs of Egypt. She lived in the 15th century B.
Historians agree that the highlight of her reign was an expedition to the fabled land of Punt, considered by some scholars likely to have been what is today Somalia. Each ship accommodated men, including sailors and thirty rowers; only returning after a two year long voyage along the African coast.
Yet the driving force for this expedition was not trade, slaves or war, but to acquire trees. Specifically the mission was to acquire frankincense and myrrh trees. When her fleet of five ships returned after the two year voyage they brought back five shiploads of various goods, yet the most prized of all their cargo was 31 live frankincense trees. The trees had been carefully excavated and their roots bound in balls of their indigenous soil for the duration of the long voyage.
Upon arrival Hatshepsut had the trees planted in the courts of her Deir el Bahari mortuary temple. When these exotic trees were planted it would become the first known transplanting and establishment of foreign trees.
This expedition was the highlight of her reign and it was the sort of accomplishment she wanted memorialising on her temple walls. So she had the expedition commemorated in relief at Deir el-Bahri. Eustatius St. Lucia St. This field is for validation purposes and should be left unchanged.
Twelve African countries, including Egypt, launched the project from Nigeria, and soon nine other countries joined the initiative. It starts from Senegal, in the far west of the continent, to Djibouti, in its east. It is scheduled to be completed by the end of Ragaei Saafan, project manager in Serapium, told Al-Monitor that using sewage water to grow a forest in the desert is a golden idea and helps boost the economy.
He explained that the treated sewage water will help transform large areas of the Egyptian desert into arable and economically viable areas. He said that the evergreen forests would purify the air, combat desertification and help reduce the high summer temperature. He added that there is a tree leaf cutter machine in the Serapium Forest, allowing cypress, pine and other deciduous conifers leaves to be used as fertilizers and feed for the livestock.
There is also a possibility to raise livestock without any significant cost, except for the potable water, he noted. Saafan pointed out that in addition to its role in maintaining soil fertility, this forest serves the local economy.
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