Polski
Science, Issue 15/2025
First global water deficit in the Anthropocene
Oct
Groundwater is an important water resource on Earth and also the basis for meeting the needs of more than half of the world’s population. However, their availability is increasingly affected by climate change and extreme weather events. An article published Sept. 23 in the journal Nature Communications analyzes the global relationships between soil water deficits, surface flows and groundwater levels from 1980 to 2020, with a focus on the Time of First Emergence (ToFE) of groundwater deficits.
In their study, researchers in Busan, South Korea, used three indices describing climatic and hydrological variability, calculated from data over 48-month periods:
- SPEI48 (Standardized Precipitation-Evapotranspiration Index), which reflects the balance between precipitation and evaporation;
- SRFI48 (Standardized Runoff Index), which describes surface flows;
- SGI48 (Standardized Groundwater Index), which indicates changes in groundwater levels.
An increasingly dry world
A marked increase in the frequency and extent of drought episodes was observed over the 40-year study period. The average values of SPEI48 indicated a systematic drying of the climate in semi-arid and Mediterranean regions, including North Africa, the Middle East and southern Europe. At the same time, SRFI48 revealed declining surface runoff in temperate zones, indicating limited recharge to river systems and aquifers.
However, the most worrisome were the SGI48 values – the index showed a global downward trend, indicating declining groundwater levels in many regions of the world. Particularly strong changes affected the southern United States, northern India, northern China and the Middle East, where the rate of decline exceeded 0.02 SGI units per year.
When the deficit begins – the concept of ToFE
One of the most important results of the study was to determine when the groundwater deficit first appeared (ToFE). ToFE was defined as the first year in which long-term groundwater drought (DZD) became statistically significant and persisted for consecutive years. In other words, ToFE marks the point at which a local aquifer system enters a state of chronic scarcity from which it does not return to its previous level of renewability.
The analysis showed that ToFE appeared globally as early as the 1990s, but its spatial distribution varied. In arid and semi-arid regions (e.g., the Middle East, Indian Peninsula, southwestern US), the groundwater deficit appeared earlier – between 1985 and 1995. In temperate zones, the moment came later – after 2000, and in tropical regions, many areas have yet to show sustained ToFE.
The average global time of emergence of ToFE for drought-affected areas was about 24 years from the beginning of the period analyzed, meaning that most regions of the world experienced their first permanent groundwater deficits as early as around 2004.
Relationships between indicators and delayed groundwater response
Correlations between the indicators confirm that changes in the climate system have clear but delayed effects on groundwater. The average global correlation coefficient between SPEI48 and SGI48 was 0.45, and between SRFI48 and SGI48 was 0.52. This means that climatic conditions and surface runoff strongly affect the groundwater balance, with a staggered effect: in many regions, groundwater only responds to drought after 6-18 months.
The researchers point out that the earlier onset of ToFE in regions with fast surface runoff confirms this relationship – where precipitation does not infiltrate deeply, the deficit appears earlier and perpetuates faster.
Regional variation and long-term effects
Areas where the ToFE occurred as early as the 1980s and 1990s are seeing the greatest declines in groundwater levels today. In some regions of India and China, the lowering of the water table locally exceeds 0.5 meters per year, with serious consequences for population and agricultural water supply.
In tropical zones, such as the Amazon and Central Africa, the occurrence of ToFE is less frequent and more irregular, which is associated with greater variability in precipitation and the ability of the environment to regenerate. Nevertheless, the authors warn that as climatic extremes intensify, the limit of permanent deficit may shift to new areas.
Conclusion: a wake-up call for water management
The introduction of the ToFE concept has made it possible, for the first time, to globally identify the point at which local groundwater systems enter a permanent state of deficit. The results show that, for much of the planet, that day has already occurred – and groundwater scarcity will worsen if mitigation measures are not implemented.
The authors stress the need for integrated monitoring and modeling of hydrological processes, combining climate observations, satellite data and field measurements. Only in this way can future ToFE changes be predicted and groundwater resources effectively protected.
Source:
Ravinandrasana, V.P., Franzke, C.L.E. The first emergence of unprecedented global water scarcity in the Anthropocene. Nat Commun 16, 8281 (2025). https://doi.org/10.1038/s41467-025-63784-6
