Study into groundwater levels in southwestern Europe demonstrates surprising resilience

A study into multi-decadal groundwater observations published in the journal Nature in July 2024 by an international team of researchers has yielded results that show surprisingly stable groundwater levels in southwestern Europe, in spite of persistent drought conditions over the past few years. Recently, the effects of climate change and rising human water demand have led to water scarcity in southwestern Europe: in 2022, for instance, 44% of the territory of the EU and the U.K. were at risk from drought. Although groundwater use is thought to be unsustainable in the region, the researchers point out that more detailed regional assessments using measured data are missing. A previous study from 2022 showed a decline in groundwater levels  in eastern Spain, northern France, and northern Italy, based on relatively coarse satellite data. The recent study in Nature, however, is based on direct observations from wells, which in most cases have been measured and documented for at least the last ten years.  

The researchers took as their starting point the analysis of water levels in 12,398 wells in Spain, France, Italy and Portugal, major fruit and vegetable-producing countries, over a 60-year period (1960-2020). The research is unique in that it brings together several factors at the same time, combining time, scientific knowledge and, what the authors call “effective international governance”, in a context of growing demand for water use. The authors describe their work as an “ideal reference for other regions of the world” facing similar difficulties. This work is singular in that it is the first of its kind and enables regional groundwater changes and their drivers to be studied in a variety of climates using field monitoring data. The authors also caution against overreliance on satellite observation for this type of survey, highlighting inconsistencies between their readings and those of satellite systems in some cases.

In the countries which were covered by the research, they note that in the selected countries, between 30-50% of irrigation water is sourced from groundwater, while between 28-75% of drinking water supplies are also sourced from aquifers. Surprisingly, they found that only 12% of the wells in the study have experienced falling water levels, while in 20% of the cases, water levels actually rose. In 68% of the cases, water levels remained relatively constant, leading to the conclusion that groundwater levels have been surprisingly stable in the face of both climate change and increased human pressures.

During the decade from 1995-2004 decade, precipitation levels were higher than the preceding decade from 1985-1994 period, but on the other hand, the scientists noted an “overall increase in annual potential evapotranspiration”, resulting in drier conditions in the summer months. Using the available data, it was thus found that the majority of the study area has experienced a steady decline in soil moisture, correlated with an increase in meteorological droughts (1985-2014), but that it is indeed soil moisture that has the greatest impact on groundwater levels.

Nevertheless, the outlook on climate change in these regions is worrying. Specialists are predicting a 15% to 30% drop in summer rainfall, which is useful for agriculture during this period.

The study highlights the complex interaction between human activities and climatic factors in the evolution of falling and rising well levels in the region. Depending on geographical factors - urban/rural areas, local agricultural activity, temperate or semi-arid climates - the situations can be very different. The human factor is extensively documented in this study, particularly in terms of how rationally the resource is managed.

In the future, agricultural droughts are expected to be more frequent, longer and more intense, impacting groundwater due to increased irrigation demand and reduced infiltration of water into the soil. Crops such as corn, olives, fruit and tomatoes will be affected.

The scientists conclude that wider access to data and increased monitoring of levels are therefore crucial to sustainable groundwater management.