Trends and shifts in groundwater levels across metropolitan France

Groundwater is the principal buffer of France's water security, yet its long-term response to intensifying climate variability and rising demand remains unresolved. We analyse 2000-2023/2024 in situ water-level records from 2536 piezometers across 717 aquifers, using Theil-Sen trend estimation with Mann-Kendall significance testing, and derive trend estimates at aquifer and city scales. A clear geographic divide emerges: aquifers in the south, southwest and Mediterranean fringe show widespread and locally steep declines, whereas northern and northwestern systems, including the Paris Basin, exhibit statistically significant but smaller-magnitude recoveries. Partitioning the record at 2015 reveals intensified deterioration in many southern and Mediterranean aquifers, while several large systems along the Atlantic margin and in northern France show incipient stabilisation. To our knowledge, this is the first high-resolution, in situ national assessment in metropolitan France to evaluate long-term groundwater trends and their evolution since 2015. These hotspot maps and multi-scale diagnostics can guide extraction limits, prioritise recharge efforts, and strengthen drought planning, setting a national benchmark for groundwater vulnerability under climate stress.