“Mega-basins are a mal-adaptation to present and future droughts”

“Mega-basins are a mal-adaptation to present and future droughts”

“A sustainable and equitable water future is possible. This requires a radical change in the way we appreciate, manage and use water. It starts with treating water as our most valuable global public good, essential to the protection of all ecosystems and all forms of life. »

These writings open the summary report on the economy of water published during the United Nations Water Conference organized from March 22 to 24, which follows an exceptionally little rainy winter in France. The developing crisis and the associated restrictions underline the importance of the management of natural storages providing a large part of the water on which we depend.

Because if water is a renewable resource, the balance is being broken as the combined effects of climate change and overconsumption of water increase. Whether in lakes, rivers, soils or groundwater, the quantities of water are decreasing in France. It is therefore very likely that competition between the main uses of water (industry, drinking and sanitary water, cooling of power stations, agriculture) will increase.

Our food sovereignty under threat

Agriculture currently uses 45% of the water consumed in France, mainly through irrigation, and represents more than 90% of summer consumption in certain regions. In a context of scarcity of available water, it is therefore crucial to (re)think our agricultural system. An adaptation is essential, but which one?

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The megabasins, which are open-air reservoirs filled in winter by pumping groundwater, are regularly presented as necessary to “feed France”. Projects are multiplying in New Aquitaine, Pays de la Loire, Center and Brittany, among others. Hydrologically and economically, mega-basins threaten water conservation and our food sovereignty.

They are first of all a poor adaptation to present and future droughts, which will increase our vulnerability while weakening ecosystems. These reservoirs depend on underground recharge and cannot cope with a prolonged drought, leaving the water tables at levels that are too low. A filling of mega basins relies on a satisfactory groundwater recharge in winter, when the hydrogeological forecasts cannot exceed six months.

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These reservoirs “short-circuit” part of the slow transit of groundwater which are real hydrological buffers in the landscapes, and can create “anthropogenic droughts” amplifying the impact of meteorological droughts downstream of water withdrawals, as already observed in the Iberian Peninsula and Chile.

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