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According to scientists, the impact of the “Great Green Wall” – which is currently being built by planting trees for millions of hectares along the African Sahel region – will go beyond just stopping the progress of the desert sands to the south and providing food for the population, to also include the impact on the region’s climate. How is that?
The Green Wall project, which was launched in 2007 and is about 8,000 kilometers long and 15 kilometers wide, aims to plant 100 million hectares of trees by 2030 along the African Sahel region. It is a semi-arid region that stretches on the southern edge of the Sahara desert from Senegal in the west to Djibouti in eastern Africa. Its completion rate is now approximately 15%. Supporters hope that the wall will prevent the desert from expanding south, as well as contribute to improving food security and creating millions of jobs in the region.
Local and global influences
But a new scientific study showed that the green wall will have a deeper impact than expected on the climatic indicators of the region. The researchers expected – according to a report published on the website “Science News” – that this project, when completed, would double the amount of rain in the Sahel region, and reduce the average summer temperatures throughout North Africa and the Mediterranean.
But the results of the simulations, which were presented last December at a meeting of the American Geophysical Union, also indicate that temperatures may become hotter in the future in the hottest parts of the desert due to the effect of this green wall.
To investigate the potential impacts of the green wall on climate, climatologist Francisco Busata from the University of Quebec in Montreal, Canada, devised a high-resolution computer simulation of the evolution of global warming in the future.
The researcher adopted two scenarios in this simulation, one with a wall of plants along the coast and the other without it. The results showed that the Great Green Wall would reduce the average summer temperature in most of the Sahel region by up to 1.5 degrees Celsius.
The monsoon winds are the means of influence
The simulations also suggest that the effects of desert greening may extend far beyond the region. Strong monsoons in West Africa can change patterns of atmospheric circulation to the west, affecting other weather patterns such as El Niño and altering tropical cyclone tracks.
Previous studies of the region’s climate in the past have shown that the “greenness of the desert” is associated with changes in the intensity of the monsoon winds in West Africa. This major wind system pushes hot, dry air toward the southwest from North Africa during the cooler months and brings slightly wetter conditions toward the northeast during the hotter months.
Scientists say that these changes in the intensity of the monsoon winds, as well as their north or south direction, led to the Green Desert period, which lasted from about 11,000 years to 5,000 years ago.
More vegetation “helps create a local pool of moisture”, as the natural water cycle intensifies from the soil to the atmosphere, increasing moisture in the atmosphere, Deepak Chandan, a paleoclimatologist at the University of Toronto who was not involved in this work, told Science News. Hence precipitation.
Plants also make the surface of the earth darker compared to the desert sand, absorbing more heat and reducing the amount of dust in the atmosphere. All of these effects lead to more heat and moisture over the oceans, which creates a larger difference in atmospheric pressure and makes the monsoons stronger and more intense.
According to the scientists, the impact that the African Green Wall may have on the local, regional and global climate still needs further study, and an understanding of past changes in the climate of the Sahara Desert will improve simulations of its future climate and understand the true impact of such a massive project.
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