According to a study published in the journal Science, the amount of water is decreasing in more than half of the world’s lakes and reservoirs. Consequence of the excessive use of this resource by humans and climate change.
“Lakes are greenhouse gas sinks”, explains Friday May 19 on franceinfo Jean-François Crétaux, CNES engineer and scientific manager of the Swot mission. “When they dry up, they can in turn generate a significant re-emission of these greenhouse gases. So that has an accelerating effect on global warming”adds the co-author of a study published in the journal Science, which reveals that more than half of lakes and reservoirs are losing water. The main fault is global warming and the excessive use of this water by man.
franceinfo: Why is this observation so alarming?
Jean-François Crétaux: Because we have seen a decrease over the last 30 years in the water contained in the great lakes. In this study, we worked on approximately 2,000 lakes, 1,000 natural lakes and 900 artificial lakes. We see a very significant decline, especially in arid areas. This will cause a number of problems, both on the amount of water available to humans, and impacts on climate change. Because lakes also play a role in reducing greenhouse gases.
Does this mean that there is a snowball effect with the drying up of large lakes and reservoirs?
Yes, because lakes are sinks for greenhouse gases, especially methane. And when they dry up, much like what happens with the melting of permafrost, they can in turn generate a significant re-emission of greenhouse gases. So it has an accelerating effect on global warming.
Have you identified affected sites in France?
Not in this study, because we worked on the 2,000 largest lakes in the world. On the other hand, we have a satellite mission which was launched by CNES and NASA three months ago, which is called Swot, and which makes it possible to work on two to six million lakes. This can help to see the role that lakes in France have on global warming and how they will evolve over time.
Fresh water is a vital resource. Can its scarcity lead, or is already leading, to population displacements in the world?
Yes, it can. There is the issue of scarcity, which will cause economic loss, especially for those who live from agriculture and who are forced to move. We experienced this in Central Asia or in the Sahel. But in other regions, on the contrary, there is a fairly strong rise in the level of the lakes due to an increase in precipitation and which causes destructive floods. We have the city of Bujumbura around Lake Tanganyika, in Burundi, which has been very heavily flooded in recent years.
The conclusions of this study are quite fatalistic or on the contrary, are you telling us that there is still time to act for our water resources?
The purpose of the study is to make an observation, rather than to say whether it is possible to act or not. We have a water resource that we can hardly control, it is linked to natural events. We can control it upstream, because it is linked to climate change. But above all we will be led to say: be careful, this water is limited and we need it. So it may be necessary to change the uses or manage it intelligently. But our study is above all there to say: this is what is happening.