Water is not only becoming scarcer in several regions of the world. It is also becoming more variable and unpredictable, with periods of drought and floods following one another in different parts of the planet. It is one of the main concerns highlighted by experts in the wake of the World Meteorological Organization’s (WMO) latest report on the state of global water resources.
“The report shows that the variability of water, and not just its scarcity, is becoming a decisive global challenge,” says Jennifer McKay, professor of Business Law at the University of Adelaide, in a reaction released by the Science Media Centre.
The expert draws attention to the fact that several regions are facing more frequent changes between droughts and floods, while trends in the storage of fresh water and the mass of glaciers continue to decline.
The WMO report shows that 2025 was one of the years with the lowest river discharges in more than three decades. Flows were below normal across 36% of the area of global river basins and, for the seventh consecutive year, basins with conditions considered “normal” were a minority.
Between 1991 and 2020, on average, 46% of basins exhibited normal conditions. In the last seven years, that share ranged from 34% to 38%.
“A more fragile world”
For Mattia Saccò, a researcher at Curtin University, the situation is particularly worrying because the decline is not limited to rivers.
“The report highlights alarming declines across all major components of the global water cycle,” says the researcher, referring especially to the loss of reserves such as glaciers and groundwater.
These reserves are especially important because they serve as sources of water during periods of insufficient precipitation. Their degradation can have consequences that go beyond immediate water availability, affecting biodiversity and the stability of ecosystems.
Saccò also warns of potential cascading effects, including the degradation of forests and wetlands dependent on groundwater and the salinization of soils, with consequences for ecosystems and agriculture.
In his assessment, the combination of these trends is making the world “more fragile.”
Droughts, floods, and little time to recover
The succession of extreme events is another aspect highlighted by the experts. According to the WMO, in the last five years national meteorological and hydrological services reported record floods and droughts in different regions of the world.
In some places, there was virtually no time to recover between one extreme event and the next.
Between 2021 and 2025, the La Plata and Amazon basins, the Middle East and the Horn of Africa registered persistent droughts lasting several years. Conversely, severe floods repeatedly hit regions of West and Central Africa and Southeast Asia.
Asia and Africa were the regions most affected by hydrometeorological extremes in 2025. Together, they accounted for at least half of water-related extreme events recorded in the last five years and more than 80% of deaths associated.
For Jennifer McKay, these data show the need to change how water management is planned.
The expert argues that long-term decisions should take greater climate variability into account, rather than relying exclusively on historical patterns of rainfall and water availability.
Glaciers and groundwater under pressure
The instability of the water cycle is accompanied by a slower, but equally significant, trend: the reduction of water reserves.
Terrestrial water storage has shown a persistent negative trend since 2014-2016. This indicator includes groundwater, lakes and rivers, soil moisture, vegetation, snow and ice.
Glaciers lost 408 gigatonnes of mass during the 2025 hydrological year, with all major glaciated regions recording losses for the fourth consecutive year.
Groundwater also shows signs of stress. Between 2022 and 2025 persistent deficits have been observed in several regions, including parts of Europe, the Americas, the Middle East, India, Southern Africa and Australia.
Mattia Saccò considers that this evolution should be closely monitored, due to the importance of groundwater for ecosystems and for water availability.
More data to anticipate extremes
Experts also emphasize the importance of improving monitoring. Although the amount of information available has increased, Africa and Asia remain among the regions with the fewest hydrological observations, despite being among the most affected by extreme events.
For McKay, reliable hydrological information is essential for managing risks to communities, agriculture, ecosystems and infrastructure.
The WMO itself advocates greater data sharing and common early warning systems. The reason is simple: water systems do not respect political borders. A change in a river basin or in the melt regime can affect populations located hundreds of kilometres away.
The WMO report, which brings together data from meteorological and hydrological services, researchers and other institutions, tracks 15 hydrological variables, from river discharges to groundwater, snow and ice.
The scenario drawn is not only that of a planet with less water available in some regions. It is also that of a hydrological cycle that is harder to predict and, according to the experts, this requires rethinking how societies prepare for the water they have and for the water they no longer have.
