La quantité d'eau potable dans le sous-sol africain
Category
📚
ÉducationTranscription
00:00 The amount of drinking water in the African subsoil is estimated to be 660,000 km3.
00:06 That's a little over 100 times more than the amount of rain that falls on the surface every year.
00:13 On this continent, as elsewhere, almost everywhere in the world,
00:16 the subsoils seem to be overflowing with an almost inexhaustible amount of fresh water.
00:22 It's easy to imagine that by draining it, we can solve all the problems of access to drinking water.
00:27 But in reality, on average, only a tenth of these subsoil resources are actually exploitable.
00:34 In the Libyan desert, the rains of the highly controversial Project of Great Artificial Rivers,
00:39 which exploit the precious subsoil blue gold reserves,
00:42 are already falling to more than 400 meters deep.
00:46 And we think that at the rate at which we hit it,
00:48 in 50 years, these aquifers should be about 100 meters lower than they are today.
00:54 As gigantic as they are, these reserves, which took millennia to form,
01:00 are unfortunately not eternal.
01:02 Let's take the example of the immense Ogalala Aquifer,
01:05 which in the USA extends under the Great Plains of eight different states.
01:09 There, in a mixture of sand, lime, clay and gravel,
01:13 lies one of the most precious treasures on the North American continent.
01:17 Because Ogalala, not content with having a funny name,
01:21 provides drinking water to millions of Americans and indirectly feeds them as well.
01:27 In this satellite photo, we can see 1,400 square kilometers of fields,
01:31 which in Kansas are all flooded with water, drained into the groundwater.
01:35 Since 1950, the amount of water contained in Ogalala has been reduced by nearly 10%.
01:42 This may seem little, but already many wells have dried up,
01:45 and it is estimated that by continuing to drain at the rate at which they do so,
01:49 American farmers should see this aquifer dry, let's say, in about twenty years.
01:56 When we think about the fact that today,
01:58 nearly a third of the land irrigated by the United States is based on this aquifer,
02:03 we become aware of the importance of this invisible water.