Like all deserts, the boundaries of the Sahara fluctuate with the seasons, expanding in the dry winter and contracting during the wetter summer. The southern border of the Sahara adjoins the Sahel, the semi-arid transition zone that lies between the Sahara and the fertile savannas further south. The Sahara expands as the Sahel retreats, disrupting the region's fragile grassland ecosystems and human societies. Lake Chad, which sits in the center of this climatologically conflicted transition zone, serves as a bellwether for changing conditions in the Sahel.
And the lake is drying out," Nigam explained. It's an integrator of declining water arrivals in the expansive Chad Basin. A number of well-known climate cycles can affect rainfall in the Sahara and the Sahel. The AMO, in which temperatures over a large swath of the northern Atlantic Ocean fluctuate between warm and cold phases on a to year cycle, is one example. Warm phases of the AMO are linked to increased rainfall in the Sahel, while the opposite is true for the cold phase.
For example, the notable drying of the Sahel from the s to the s has been attributed to one such cold phase. The Pacific Decadal Oscillation PDO , marked by temperature fluctuations in the northern Pacific Ocean on a scale of 40 to 60 years, also plays a role. To single out the effects of human-caused climate change, the researchers used statistical methods to remove the effects of the AMO and PDO on rainfall variability during the period from to The researchers concluded that these natural climate cycles accounted for about two-thirds of the total observed expansion of the Sahara.
The remaining one-third can be attributed to climate change, but the authors note that longer climate records that extend across several climate cycles are needed to reach more definitive conclusions.
But our paper is unique, in that we use these trends to infer changes in the desert expanse on the century timescale," said Natalie Thomas, a graduate student in atmospheric and oceanic science at UMD and lead author of the research paper.
The study's results have far-reaching implications for the future of the Sahara, as well as other subtropical deserts around the world. As the world's population continues to grow, a reduction in arable land with adequate rainfall to support crops could have devastating consequences. Professor Amin Al-Habaibeh, professor of intelligent engineering systems at Nottingham…. University of Edinburgh. Queen's University Belfast. Queen Mary University of London.
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Places Riding the California Zephyr. Writer and photographer John Gilbey needed a cheap way of…. Water Europe's rivers are obstructed by 1. While the desert waxes and wanes with the drought that comes with the changing seasons, declining rainfall combined with deforestation and soil degradation has seen it grow. The creep has been particularly pronounced to the south, where it has spread into the Sahel by more than ,sq km over the same period.
The desert now covers an area of 9. It is a picture that is being replicated elsewhere. The UN estimates that ,sq km of land are lost to desertification globally every year.
The baobab fruit dries to a hard husk that needs to be cracked open to get to the dry pulp inside Credit: Aduna. But this will be far from a glorified hedgerow stretching across the continent. This has involved drawing on the knowledge of indigenous people to find local methods of caring for the land.
In Burkina Faso, Mali and Senegal, for example, farmers have been rehabilitating land by using zai, a traditional practice of building lines, stripes and semi-circles of stones that help to retain water during dry periods and allow it to soak into the hard soil. In other parts of Ghana, villagers have been planting elephant grass as a way of holding the soil together, while also using it to weave baskets.
But at the centre of the project are trees. Senegal alone has planted more than 12 million drought-resistant trees in just over a decade since the Great Green Wall was launched. We need to do much more and we need to do it at scale. Until now we have only been working with small projects led by pilot communities.
It is an ambitious target but one they hope will bring greater food security to the Sahel by improving the soil for crops and at the same time help to draw millions of tons of carbon out of the atmosphere. The success has been mixed though, and the initiative has been criticised for slow progress. Outside Africa, similar attempts by China to plant forest barriers to hold back the Gobi desert have also shown limited effects.
Indeed, there are indications that dust storms from the Gobi may have increased rather than decreased. While it is all very well asking local farmers to plant, protect and nurture trees, they will always compete with the need for food and income. But if the trees can help to produce income themselves, then there is a compelling reason for letting them grow and spread. It is hoping that products like Baobab may encourage major multinational food companies to invest in the planting and harvesting schemes that are being set up in places like the villages around Paga.
And the potential extends beyond just baobab. The leaves of the moringa tree are also growing in popularity as a health food. Native to the arid sub-Himalayan areas of India, Pakistan and Afghanistan, it is well suited to growing in conditions found in many parts of the Sahel. Shea butter, popular in cosmetics and moisturisers, comes from the nut of trees that also grow in the region.
The sandy soil in Ghana is extremely vulnerable to erosion without trees and other vegetation to hold it in place Credit: Alamy. Andrew Hunt from Aduna also sees promise in grass crops that are traditionally grown in West Africa such as fonio, a type of millet that can be made into a cous cous-like product and could give other trendy grains such as quinoa some tough competition.
But there are some who have concerns about what might happen if large multinational companies and food manufacturers start creating a wider demand for these crops. While it can bring valuable income and investment into an area, there is also a danger of over exploitation or even the creation of new mono-crops, much like the vast palm oil plantations that now dominate large parts of southeast Asia, Central America and South America.
This might only exacerbate some of the problems that are driving desertification in the first place, warns Lindsay Stringer, an expert on land degradation and water at the University of Leeds in the UK.
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