Drought. “The less water there is, the more its quality deteriorates”

Florence Habets Director of research at the CNRS

While the Alps are facing a particularly severe episode of drought, Florence Habets, researcher for the CNRS at the Geology Laboratory of the École Normale Supérieure, discusses this phenomenon and its impacts.

Will the current drought in the Paca region be repeated?

This is a severe episode. But, if we actually expect it to repeat itself, it does not for all that presage a dry continuity from next year. That is why we are talking about projections and not forecasts. While it is possible to anticipate trends, extreme events remain difficult to predict. Precipitation, for example, is particularly complicated to estimate reliably, because it is linked to a very strong interconnection with the oceans and the sea. At altitude, on the other hand, the disappearance of the snowpack makes it possible to provide fairly clear indications. At this time, the glaciers are melting fast, which helps to maintain a flow of water. But this only has a time and it is expected that these flows, with the disappearance of the glaciers, will decrease sharply in the future. When we talk about water resources, we are talking about the part of rain that does not evaporate. However, with rising temperatures, evapotranspiration increases and water resources decrease in the region.

Alongside the climate issue, isn’t there also a resource management problem?

Water resources are only part of the problem. We consume more than one planet per year. And, in terms of water, not only are we depleting the resource but, in addition, we are polluting it. Our dependence on water, particularly in agriculture, is worrying. The intensification of crops has created phenomena of scarcity at the local level. To consider that the resource is inexhaustible and the growth infinite, we are going straight into the wall. The wall of a dry dam.

What are the consequences of drought on biodiversity?

The first victims of a drought are the fish that die in waterless rivers. But all biodiversity is affected since animals drink. Diverting the water into reservoirs or pumping it into groundwater aggravates the problem. The vegetation also suffers from this water stress, one of the consequences of which is the multiplication of forest fires. A whole ecosystem is disappearing. At the same time, we know that the less water there is, the more its quality deteriorates. High temperatures accentuate the proliferation of algae and promote water intoxication, which threatens all aquatic life.

Does this phenomenon concern other regions in France?

The water deficit is particularly marked in the south of France, but we are also seeing a rainfall deficit in Poitou-Charentes, where the groundwater level is extremely low and should remain so until at least October. The degradation of groundwater levels also concerns Hauts-de-France and Grand-Est. Groundwater is 60% drinking water, 40% irrigation and 30% industrial water. It is not negligible. They are a formidable natural storage system from which water flows continuously and feeds the rivers. Their level drops and then rises in winter, during periods of high water. When it does not rain enough to fill the rivers, the sheets take over. But this year, they emptied more than they filled. The risk in the future is to see a combination of the two types of drought, in the sheet and on the surface.

Could this drought cause a drinking water supply problem?

Drinking water supply problems during periods of drought are generally associated with a deterioration in water quality. When the resource runs out, we will take water from where it deteriorates and is therefore no longer drinkable.

Can we imagine Europe becoming a desert area?

Climate projections show that two areas in the world are particularly at risk from drought: southern Europe and the Gulf of Mexico. There, huge dams are already completely empty, without the possibility of irrigating crops or producing hydroelectricity. This is a very serious situation which also affects highly populated regions. Massive migrations are to be expected. In France, there are already municipalities which, because of the lack of drinking water, can no longer afford to welcome new inhabitants and refuse building permits. The only way to ward off this phenomenon is to drastically reduce our greenhouse gas emissions. Climate and drought are totally connected.