Why is the water cycle now considered unstable?
The water cycle moves moisture from land and oceans into the atmosphere and back as precipitation. Satellite observations compiled by the WMO show that total freshwater stored on land has declined each year since 2016. In 2025, 42 percent of monitored areas recorded storage below the long-term average. The same data set indicates that 2025 ranked among the three driest years for global river discharge in more than three decades. The WMO states that the cycle has become more unstable and unpredictable because of pollution from fossil fuels that drives climate change. Wayne Jenkinson, director of the WMO hydrology and cryosphere division, notes the trend is clear: land water storage has been falling worldwide since around 2016. The report finds that seven consecutive years of abnormal river flows have now occurred, with a larger share of basins below average than above. Celeste Saulo, WMO secretary-general, describes the slow-changing stores of glaciers, snow and ice as the planet’s savings account that once buffered single bad years; that account is now being drawn down faster than it can be replenished. The source material leaves open how quickly societies can adapt once this buffer is exhausted. Rivers, lakes, aquifers, ice, snow and soil together hold the planet’s freshwater reserves, and the WMO analysis shows this total volume is shrinking. Jenkinson underlines that the direction of change is consistent across continents, while Saulo stresses that the slow stores no longer provide the same protection against isolated dry spells. The report therefore concludes that the cycle itself has shifted into a persistently unstable state.
Which regions recorded the largest river-flow deficits?
Below-average flows affected large parts of North America, eastern Europe, the Middle East and central Asia. In Europe the Rhine and Danube fell low enough in places to interrupt navigation. Two-thirds of the groundwater wells tracked by national agencies also showed levels outside historical ranges, with the balance shifting further toward deficit compared with 2024. The affected zones include much of North America, parts of South America, eastern Europe, the Middle East and central Asia. Rivers remain vital arteries for trade, drinking water, agriculture, industry, hydropower, wildlife habitat and tourism, so reduced flows carry immediate economic and ecological costs. The same pattern appears in groundwater: two-thirds of monitored wells sat outside historical norms in 2025, and the deficit is widening relative to 2024. The report notes that some basins still recorded above-average flows, yet the overall share below average was larger, confirming the long-term drying trend. Navigation on the Rhine and Danube was halted at several points, while agriculture and hydropower operators faced reduced supply. The same drying signal appears in aquifers, where the share of wells below normal rose further from the already elevated 2024 figure. These overlapping deficits across surface and subsurface stores compound the pressure on water users in the listed regions.
How much glacier ice was lost between 2023 and 2025?
Every monitored glacier region recorded net loss for the fourth consecutive year. The combined volume lost equals the water needed to fill roughly 560 million Olympic-size swimming pools. Continued retreat raises flood risk in the short term and threatens long-term water supply for the two billion people who rely on glacier melt. All glacier regions showed expanded loss in 2025. The three-year total (2023-2025) represents enough water to fill about 560 million Olympic pools. Saulo warns that the traditional buffer role of these slow stores is being exhausted, leaving societies more exposed when a single dry year arrives. The source does not quantify how many additional years of current loss rates would empty the remaining buffer entirely. The four-year run of net loss means the cryosphere component of the water cycle is now contributing to rather than offsetting annual variability. For the two billion people whose water supply depends on glacier melt, the continued draw-down reduces the volume available in future dry seasons and increases the likelihood of both floods during rapid melt events and shortages later in the year.
What extreme events accompanied the hydrological changes?
Record floods struck Texas in July 2025, causing more than 130 deaths. Hurricane Melissa crossed Jamaica and Haiti, killing more than 90 people. At the same time, drought conditions intensified across the eastern Mediterranean and parts of the Middle East. The WMO notes that recovery time between successive extremes has shortened in many basins. Asia and Africa recorded the highest numbers of events and the greatest loss of life. Nigeria and the Democratic Republic of Congo suffered severe flooding; parts of South and Southeast Asia were hit by tropical cyclones and intense monsoon rains. In the opposite direction, eastern Europe, the Mediterranean and the Middle East faced serious drought. Saulo adds that the strengthened El Niño in 2026 will raise flood risk in some areas and drought risk in others. The report leaves unsettled the precise attribution of each individual event to the long-term hydrological shift. The shortened recovery intervals mean communities have less time to rebuild before the next event, amplifying cumulative damage especially in Asia and Africa where both frequency and fatalities were highest.
Where are the main data gaps?
More than 60 countries contributed observations, yet coverage remains sparse across parts of Asia and Africa where extremes are most severe. Without denser networks, agencies cannot quantify the full extent of storage losses or issue reliable early warnings. Officials stress that management decisions require measured data rather than estimates. Mattia Sacco of Curtin University, who did not contribute to the report, says it highlights alarming degradation trends across all major components of the global water cycle. He notes that rapid losses in both quality and quantity of water threaten biodiversity, weaken ecosystems and leave the world more vulnerable overall. Jenkinson emphasises that gaps must be closed because “we cannot manage what we do not measure.” The source indicates these gaps persist mainly where extremes are strongest, limiting the reliability of global assessments. The absence of dense monitoring in the very regions experiencing the strongest extremes reduces the precision of early-warning systems and leaves the true scale of storage decline only partially documented.
Frequently asked questions
What does the WMO mean by “abnormal river flows”?
The term covers years when annual discharge deviates significantly from the 1991-2020 baseline. Seven such years have now occurred in succession, with more basins below average than above.
Are the observed changes reversible?
Reducing emissions would slow the rate of glacier loss and allow storage to stabilise over decades, but some ice already lost will not return within human time scales.
Which sectors feel the effects first?
Navigation, hydropower and irrigated agriculture register shortages earliest because they depend on predictable seasonal flows that are now more variable.
Does the report cover groundwater quality?
No. The current assessment focuses on quantity; quality indicators are collected by separate programmes and are not yet integrated at global scale.
Will El Niño increase risks in 2026?
The WMO expects elevated flood probability in some regions and heightened drought risk in others, consistent with the typical El Niño pattern observed in previous events.
