What shrinking glaciers and falling groundwater levels mean for the future

The planet's water cycle is becoming increasingly erratic, swinging between too little and too much, the United Nations has warned, with an unprecedented El Niño expected to exacerbate the long-term trend.

Last year was among the driest for the world's rivers in over three decades, the UN's World Meteorological Organization (WMO) said in a report.

In 2025 — one of the warmest years on record — glaciers also shrank across all regions, even as groundwater levels in many parts of the world are in multi-year decline, it found.

Overall, the WMO's annual State of Global Water Resources report showed that Earth's freshwater storage — the total amount of water stored in groundwater, lakes and rivers, soil moisture, vegetation, and ice and snow — continued its decade-long decline.

Some elements of the water cycle change rapidly — like precipitation, river flow and soil moisture, responding to weather within days or weeks.

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WMO secretary-general Celeste Saulo voiced particular concern about the decline in "slow reserves", like groundwater and glaciers, which she said had traditionally served as the planet's "savings account".

They 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", she told reporters.

Now, "we are depleting that savings account", she warned. "We are spending our reserves."

Glaciers have also been shrinking at a precipitous rate, with 2025 marking the fourth consecutive year when they shed significant ice mass across all regions.

Between 2023 and 2025, the report estimated that glaciers lost a cumulative global glacier mass of 1,400 gigatonnes of water — roughly equal to the water required to fill 560 million Olympic-sized swimming pools, or about a third of the world's annual freshwater withdrawals.

"Groundwater tells a similar story: nearly two-thirds of monitored wells worldwide showed conditions outside the historical norm in 2025," Saulo said.

She highlighted that this was happening in parallel with "more water-related disasters".

In particular, she pointed to the current El Niño pattern, which is expected to be the strongest since comparable records began four decades ago.