The world’s water cycle is becoming increasingly unpredictable, with freshwater supplies swinging between extreme shortages and excesses, the United Nations has warned.
The warning was contained in the World Meteorological Organization’s (WMO) latest State of Global Water Resources report, which found that freshwater storage continued its decade-long decline in 2025, one of the warmest years on record.
According to the report, 2025 was among the three driest years for global river flows in more than three decades, while glaciers continued to lose significant amounts of ice across all regions. 
The WMO also reported that groundwater levels were declining in many parts of the world, adding to concerns over the long-term availability of freshwater.
WMO Secretary-General Celeste Saulo said the most worrying development was the depletion of what she described as the planet’s “slow reserves”—groundwater and glaciers that traditionally provide a buffer during periods of drought.
“These reserves have served as a buffer that absorbs bad years so that a single drought or a single dry season does not translate directly into a water crisis,” Saulo told reporters.
‘We Are Spending Our Reserves’
Saulo warned that humanity was increasingly drawing down these natural reserves.
“Now, we are depleting that savings account. We are spending our reserves,” she said.
The report estimated that glaciers lost a cumulative 1,400 gigatonnes of water between 2023 and 2025. The amount is equivalent to the water needed to fill about 560 million Olympic-sized swimming pools and represents roughly one-third of the world’s annual freshwater withdrawals.
Groundwater is also showing signs of increasing stress. Saulo said nearly two-thirds of monitored wells worldwide recorded conditions outside their historical norms in 2025.
The decline in freshwater reserves is occurring alongside a rise in water-related disasters, according to the WMO.
Rivers Record Abnormal Flows
The report found that river flows remained highly abnormal in many parts of the world even before the latest El Niño conditions intensified.
For the seventh consecutive year, river basins recording normal conditions represented a clear minority globally.
Only about 36 per cent of monitored river basins recorded normal flows in 2025. Another 36 per cent experienced below-normal discharge, while 21 per cent recorded above-normal flows.
The figures underscore growing instability in the global water cycle, with some regions experiencing severe shortages while others face excessive rainfall and flooding.
El Niño Could Deepen Extremes
The WMO also raised concerns about the potential impact of El Niño, the warm phase of a naturally occurring climate cycle that develops every two to seven years and affects global rainfall, winds and weather patterns.
Saulo warned that the strengthening El Niño could increase the risk of drought in some parts of the world while raising the likelihood of flooding elsewhere.
The phenomenon is characterised by unusually warm ocean temperatures across the Pacific and can trigger significant changes in weather patterns far beyond the region.
WMO Calls for Better Data
The UN agency stressed that reliable and shared water data would be critical to managing the growing risks.
The WMO said significant gaps remain in hydrological monitoring, particularly in regions already experiencing severe water stress.
“Weather respects no borders, and this is especially true for water,” Saulo said, calling for “shared data, shared standards and shared early warnings”.
She noted that river basins often cross national borders, meaning water conditions in one country can have consequences downstream in another.
“A river basin is fed by water upstream, often in another country,” she said, adding that disasters affecting glaciers or other water sources could also have cross-border consequences.
