Groundwater reserves in southeastern Europe are more stable than expected
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An international research team, in which IIAMA-UPV participates, discovers that groundwater levels are not decreasing everywhere, as previously believed, but mainly in semi-arid regions with intensive agriculture and droughts
Groundwater is a vital resource that supports plants and ecosystems, ensures agricultural production and serves as a central component of drinking water supply. However, climate change and anthropogenic pressures may threaten groundwater availability, especially in southwestern Europe.
In an article recently published in Communications Earth & Environment, a journal belonging to the prestigious scientific publisher Nature, this situation was evaluated by an international research team coordinated by the Helmholtz Centre for Environmental Research (UFZ) and in which Jaime Gómez, head of the Hydrogeology group at IIAMA-UPV (Institute of Water and Environmental Engineering at the Universitat Politècnica de València), participated, using historical series of more than 12,000 groundwater wells in Portugal, Spain, France and Italy.
The surprising result is that groundwater levels are not declining everywhere, as previously believed, but mainly in semi-arid regions with intensive agriculture and frequent droughts.
Declines are also observed in temperate regions associated with large urban areas. Finally, the authors conclude that, with appropriate management practices, groundwater can be used sustainably.
“A widespread belief is that groundwater levels are continuously declining throughout southwestern Europe. However, a closer look at the data reveals that the situation is more complex and each situation depends on the regional socio-economic context and reality,” says UFZ hydrologist Dr. Seifeddine Jomaa, author of the study.
Historical context, evolution and regional situation
Data from 1960 to 2020 revealed that 68% of the wells examined showed stable levels over the past three decades, 20% of the wells showed an increase in groundwater levels, while only 12% showed a decrease.
“To avoid generalisations, a differentiated and detailed consideration of groundwater at the local level is needed,” says Seifeddine Jomaa.
Stable groundwater levels are mainly located in mesothermic climate regions with high rainfall throughout the year, such as northern France.
“In these regions, high recharge rates keep groundwater levels almost stable,” says Rafael Chávez García Silva, first author and also a hydrologist at UFZ.
In other areas, such as the lower Po River basin near Ravenna, groundwater levels are rising due to natural and anthropogenic factors and land subsidence, requiring drainage of surface water and pumping of groundwater to prevent flooding.
In semi-arid regions, however, there are places such as Tarbes in France and Medina del Campo in Spain where groundwater levels have been falling for decades. This is partly due to decreased rainfall and high temperatures caused by climate change. Intensive agriculture is also a major factor.
“These four Mediterranean countries are responsible for a large part of the EU’s fruit, vegetable and cereal production, and groundwater supplies between 30% and 50% of irrigation,” says Seifeddine Jomaa.
Even in temperate regions, the researchers found wells with declining groundwater levels, caused by proximity to cities and industry.
“Since the 1960s, for example, groundwater levels in metropolitan areas of cities such as Lyon, Nice, Modena and Bordeaux have been declining. In Bordeaux, France’s ninth-largest city, high groundwater consumption is attributed to increased domestic use. The popular French tourist destination, Béziers, has seen a significant decline in groundwater levels due to increased extraction to supply drinking water to summer tourists,” the authors explain.
Holistic and sustainable management approaches
While groundwater decline in urban and industrial areas is not easily stopped, researchers have found effective management approaches in semi-arid agricultural regions, leading to the recovery of groundwater levels, as seen in La Mancha Oriental in Spain.
“Until the 1990s, groundwater levels were declining due to over-irrigation. As a result, stretches of the Júcar River dried up in 1994 for the first time in history. This dramatic event prompted farmers to create a water user association that aimed to stop the decline in groundwater levels through a combination of monitoring, remote sensing and individual water use plans. These measures effectively reversed groundwater level trends in the region,” says co-author J. Jaime Gómez-Hernández, professor of Hydraulic Engineering at the UPV and researcher at IIAMA.
In the context of climate change, southwestern Europe can provide lessons for groundwater management in other regions of the world, especially as demand for groundwater increases and aquifer recharge is affected by climate change.