Le désert du Sahara, l'un des endroits les plus arides de la Terre, est lentement en train de se transformer en lac ! 🌊😱 Les scientifiques ont découvert que des réserves d'eau souterraines et des changements dans les schémas climatiques apportent des modifications inattendues à ce vaste désert. Dans certaines zones, des rivières anciennes réapparaissent, et des lacs cachés se forment là où le sable régnait autrefois. 🌿 Cela pourrait-il signifier que le Sahara est sur le point de redevenir vert, comme il l'était il y a des milliers d'années ? 🤯 Si tel est le cas, cela pourrait complètement transformer la vie en Afrique du Nord et même impacter le climat mondial ! Regardez maintenant pour voir comment l'un des paysages les plus inhospitaliers de la Terre fait un retour incroyable ! 🔎🔥 Animation créée par Sympa.
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FunTranscript
00:00If you observed the Sahara from space at this very moment, you would see a surprising spectacle.
00:08An arid land sprinkled with lakes and rivers in Morocco and Algeria.
00:13All thanks to the heavy rains of early September 2024.
00:17These are not oases, it is just the Sahara that comes back to its original state.
00:22Believe it or not, there are chandeliers.
00:24One of the largest deserts on the planet was in fact a luxurious paradise full of greenery.
00:30Let's first see how the Sahara turned into a desert.
00:33During the last glacial period, the earth was much colder and large ice caps covered a large part of the emerged lands.
00:42At that time, the Sahara desert was much larger than today and there were fewer tropical forests on our planet.
00:50And because of these very low temperatures, the distribution of rain in the tropics has changed.
00:55Normally, hot air rises in these regions, which contributes to precipitations.
01:01But as it was colder during the period we are talking about, the weather has been disturbed and there is less rain in some areas.
01:09This gave us a drier climate in places that are generally more humid.
01:14There was also a lot of dust in the Sahara desert.
01:18Scientists found it in old ocean sediments.
01:21But about 12,500 years ago, something amazing happened.
01:26Dust levels have dropped sharply.
01:29This means that the Sahara has become much more humid and indicates that the climate has suddenly warmed up for a while before cooling down again.
01:3912,500 years ago, the Sahara has therefore become a much greener place, like a savannah.
01:44Because a meteorological phenomenon called the Intertropical Convergence Zone, yes, that's what it's called, was moving north during the summer.
01:52This humid period reached its peak about 4,000 years ago.
01:57The temperatures were then a little higher than today.
02:00At that time, it rained more on the high Ethiopian plateaus, which made the Nile transport more sediment.
02:08However, there was another big change, the Heinrich event, which caused the movement of the Intertropical Convergence Zone to the south.
02:17This led to a rapid drying of the Saharan regions and the Arabian Peninsula.
02:22As a result, the Nile experienced much less rain between 2700 and 2100 BC.
02:28To make it short, a little late for that, of course.
02:32The Sahara has experienced alternate periods of humidity and dryness due to climate change and meteorological conditions for thousands of years.
02:40Until recently, we had a dry Sahara.
02:43But in September 2024, an unusual cyclone crossed the region.
02:47It hit Morocco, Algeria, Tunisia and Libya and filled the dry lakes and rivers.
02:53The satellite images of the Nasa before and after the rains are breathtaking.
02:57It's as if the Sahara had made new skin.
03:00Some regions of North Africa have received up to 20 centimeters of rain.
03:05For comparison, Seattle receives about one meter per year, which is only five times what the Sahara has received.
03:12I say only for a simple reason.
03:15Seattle has the reputation of being a rainy city, unlike the Sahara.
03:19The difficulty lies in the fact that these 20 centimeters, which is the equivalent of the total rainfall in the region, fell in a few moments.
03:28So, in a way, we could have had the impression that it was raining more in the Sahara than in Seattle.
03:34The mountains have channeled the water to ephemeral lakes in northern Algeria, which have recently spread over more than 180 square kilometers and have reached a depth of more than two meters.
03:45It's enough water to last a year.
03:49So, what exactly are these ephemeral lakes?
03:52They are basins that fill up for a short period every year, but can remain dry for several years if the rain is not at the rendezvous.
04:00Sometimes, the water spills from a small surrounding area, but it can also be good old rain.
04:07Now, a big question arises. How do these lakes exist?
04:11Generally, they are formed because there is an excess of water trapped on the surface.
04:15But the Sahara soil is incredibly dry. Shouldn't it act like a sponge?
04:20It must be thirsty for moisture.
04:22Think of the thirst of your potting plant when you give it water on your return from vacation.
04:27However, however dry it is, the earth can only absorb a limited amount of water, often very low.
04:34And just like your potting plant, it does not necessarily drink it completely.
04:39Sometimes, you water it too much.
04:41And if you look below, you will see that the pot has begun to leak.
04:45Another important factor that prevents the soil from absorbing water is the lack of vegetation.
04:50In normal conditions, trees, shrubs and various plants help to retain moisture.
04:57In the desert, however, it is almost impossible.
05:00There may be a few palm trees, but that's about it.
05:04This also explains the formation of these temporary lakes.
05:07The precipitation that is not retained by the plants accumulates in the valleys and the low-altitude depressions,
05:13creating these ephemeral streams of water.
05:15These lakes may only last a short time, but that does not mean that we should not name them.
05:20For example, the magnificent lake decorated with wavy palm trees that you see here is called Lake Yasmina,
05:26located in the oasis city of Merzouga.
05:29In some areas of the desert, where the dunes rise, one might think of a mirage, but it is not.
05:35The sand dunes are partly covered with water.
05:38Do you remember that I talked about 20 cm?
05:41Well, this is not quite accurate for some regions.
05:44Indeed, there are places where the flood was so important that the palm trees were submerged to their peaks.
05:51The last time we saw such an intense downpour was 30 to 50 years ago.
05:56But this rain was more than welcome.
05:58After six consecutive years of drought, Morocco really needed it.
06:03The lakes, which had been dry for decades, like Lake Iriki, have finally received the water they needed so much.
06:10A recent analysis revealed that of the hundreds of storms that have hit the region since 2000,
06:15only six have brought enough rain to begin to fill this lake.
06:19And among them, only two have reached a higher level than the one we observed in September 2024.
06:27So, if these torrential rains seem to be a blessing, the big question is whether they will last.
06:33The answer is yes.
06:35When the humid air from the equatorial regions meets the hot and dry air from the north,
06:40the Sahara Desert tends to receive more rain.
06:43Scientists say that this collision zone is moving north as the planet warms up,
06:51and that it should therefore continue to move in this direction over the next two decades.
06:57But I may be a little too optimistic.
06:59The truth is that the news is not entirely positive.
07:03In fact, no one was really ready to face such a flood.
07:08In addition, do not forget that this is not a country in Southeast Asia where people are used to so much water,
07:13but the Sahara, an arid region.
07:16That said, I think you see where I'm coming from.
07:19Tragically, at least 18 people have lost their lives because of the intense rains in southern Morocco.
07:25And the authorities are preparing for even stronger rains.
07:29But if this is the case, could this mean that the Sahara is threatened with extinction?
07:34And what would that mean for us?
07:36It may seem a little strange.
07:38But our planet also depends on deserts.
07:40And the Sahara is no exception.
07:42At first glance, it may seem sterile and uninteresting.
07:46But deserts play a crucial role in our ecosystem.
07:50They are important CO2 storage sites.
07:53They are called net carbon wells.
07:56By itself, the Sahara would contain about 1 billion tons.
08:01In the fight against climate change, these deserts serve as a buffer,
08:06helping to maintain temperatures at acceptable levels.
08:09Yes, the deserts are burning, but they are a bit like the planet's air conditioning system.
08:15In addition, desert sand is a source of nutrients for luxurious areas,
08:20such as humid tropical forests.
08:22Believe it or not, scientists have discovered that the sand particles of the Sahara
08:27contribute to feeding the Amazon rainforest.
08:29These particles cross the Atlantic Ocean, carried by the winds,
08:33all the way to South America, where they enrich the soil of the Amazon basin.
08:37Without the Sahara, experts believe that the Amazon rainforest could be seriously threatened.