WMO report finds global water reserves in decade-long decline

The world’s freshwater reserves have been shrinking for more than a decade, and 2025 ranked among the driest years for river flow recorded anywhere on the planet in the past 35 years, according to the World Meteorological Organization‘s State of Global Water Resources report, released September 17.

The report found that terrestrial water storage, the combined total of groundwater, soil moisture, snow and surface water, has been declining since 2014 to 2016. The WMO described the trend as “a persistent, decade-long signal” rather than the kind of variation that shows up and reverses within a single year. Below-normal river flows covered 36 percent of the world’s river basin area in 2025, and for the seventh consecutive year, basins reporting “normal” conditions made up a minority of the total, between 34 and 38 percent, against a 1991 to 2020 average of 46 percent.

Glaciers lost 408 billion metric tons of ice, plus or minus 132 billion tons, during the 2025 hydrological year, the WMO reported, equivalent to roughly 560 million Olympic-sized swimming pools. It was the fourth consecutive year in which every major glaciated region on Earth recorded a net loss of ice mass.

WMO Secretary-General Celeste Saulo compared the pattern to drawing down a bank account. “We are depleting that savings account,” Saulo said, referring to the groundwater, snowpack and glacier ice that have historically buffered dry periods. “Buffers that have historically protected water security… are eroding on a timescale of years,” she said, calling for “a sense of urgency, not panic.”

The water report follows a separate WMO forecast, announced earlier in September, that a “very strong” El Niño is expected to peak by the end of the year and has a near-100 percent chance of persisting through February 2027. Announcing that forecast, UN Secretary-General António Guterres said “the planet is in uncharted waters, and those waters are heating up.” Asia and Africa accounted for at least half of all recorded water-related extreme events over the past five years and more than 80 percent of the deaths associated with them, the water report found, a disparity it attributed in part to gaps in flood and drought forecasting infrastructure in those regions.

A pattern visible in this year’s disasters

The report’s regional findings echo disasters that made headlines earlier this year. Flooding across Tibet and Nepal in August killed more than 1,400 people, a toll that climate researchers have connected to the same combination of glacier melt, erratic precipitation and weak early-warning systems the WMO report describes. The WMO’s data shows glacier loss and flood risk are not separate problems: as glaciers shed ice faster than snowfall can replace it, the meltwater initially swells rivers and can trigger flash floods and glacial lake outburst events, before the long-term trend shifts toward reduced flow as the ice reserves themselves run out.

The report measures water storage using satellite gravimetry data collected by the GRACE and GRACE Follow-On satellite missions, which track small changes in Earth’s gravitational field caused by shifting water mass. River discharge figures come from a global network of hydrological monitoring stations that the WMO and national meteorological agencies maintain jointly. The full report, the State of Global Water Resources 2025, is published annually by the WMO’s Hydrology, Water and Cryosphere Division and covers precipitation, evapotranspiration, streamflow, lake and reservoir levels, and terrestrial water storage across every continent.

The WMO said river discharge in 2025 was below normal across most of South America, southern Africa and parts of Europe, while flows in central Asia and the Horn of Africa ran above normal, consistent with the wetter and drier extremes that climate scientists have linked to a warming atmosphere carrying more moisture in some regions and less in others.