The World Is Losing the Water Reserves That Help It Survive Drought

Global rivers experienced one of their driest years in more than three decades in 2025, as longer-term losses of stored water weakened the reserves that help societies withstand drought. The WMO assessment points to a growing planning challenge: managing repeated floods and shortages while tracking whether groundwater, snow and ice can continue to cushion the next shock.

The world's rivers endured one of their driest years in 35 years in 2025, but the deeper warning concerns the water held in reserve. Groundwater, glaciers and other stores that help sustain supplies through dry periods are under persistent pressure. As these reserves diminish, a poor rainy season can arrive in a landscape already less equipped to absorb it.

The World Meteorological Organization's State of Global Water Resources Report 2025 estimates that below-normal river discharge affected 36% of global basin area. Across seven consecutive years, the share of river basins recording normal flows ranged between 34% and 38%, compared with an average of 46% during 1991–2020. The figures describe a sustained departure from the historical pattern, although conditions vary sharply between regions.

For governments and water managers, the challenge is the relationship between immediate extremes and longer-term depletion. Floods and droughts demand urgent responses, while changes in underground water and ice can accumulate over years. Managing the next emergency becomes more difficult when the reserves that could soften its effects are themselves deteriorating.

The reserves that carry dry years are shrinking

Different parts of the water cycle operate at different speeds. Rainfall, river flows and soil moisture can respond to weather within days or weeks, while groundwater and glaciers change over much longer periods. WMO Secretary-General Celeste Saulo warned that the depletion of these slower reserves is weakening their traditional role as a buffer against drought and seasonal shortages.

Terrestrial water storage, which includes groundwater, lakes, rivers, soil moisture, vegetation, snow and ice, has shown a declining trend since around 2014–2016, according to WMO. Recurring deficits between 2021 and 2025 affected areas including the southwestern United States, North Africa, the Middle East and Central Asia. Such persistence makes the condition at the start of a dry season increasingly significant.

Groundwater observations reinforce that concern, although they require careful interpretation. Nearly two-thirds of monitored wells recorded conditions outside their historical norms in 2025, and the balance shifted further towards deficits compared with 2024. The proportion includes both unusually high and unusually low levels; it does not mean that two-thirds of the world's groundwater was depleted.

The practical concern is cumulative exposure. Where underground reserves remain low over successive years, households, water suppliers and water-dependent businesses may enter each new shortage with less protection. A return of rainfall can improve immediate conditions, but assessing whether the underlying deficit has eased requires evidence of recovery in storage itself.

Floods offer no guarantee of recovery

The report's regional contrasts show why a single description of the global water situation can mislead. South and South-East Asia recorded above-normal to much-above-normal river discharge in 2025, while much of North America, the Middle East and Central Asia experienced below-normal flows. Within Africa, high flows in the Niger and Limpopo basins coincided with much-below-normal discharge in the Nile, Congo and Zambezi.

Different measures also reveal different pressures within broad regions. Despite high river discharge across South Asia overall, total water storage was below normal in northern India, while groundwater deficits persisted in the northwest. These observations cover different areas and parts of the water cycle. Taken together, they show why strong river flows cannot establish that every component of regional water supply has recovered.

Signs of improvement thus need to be assessed on their own terms. The La Plata region in South America showed partial recovery from long-term drought, while much-above-normal storage continued in Central and Southern Africa. Neither development cancels the wider decline. For planning purposes, the crucial question is whether improvements persist and extend to the reserves on which future dry periods will depend.

Glacier losses put future water supply under pressure

Glaciers make the difference between immediate water flows and long-term reserves particularly visible. Melting ice can contribute to short-term hazards while reducing the stock of frozen water available in future years. WMO reports that every major glaciated region lost mass in 2025, the fourth consecutive year in which losses extended across all those regions.

The agency estimates that glaciers lost 408 billion tonnes of mass during the 2025 hydrological year, with uncertainty of plus or minus 132 billion tonnes. Central Asia, South Asia West, Iceland, the Russian Arctic, and Western Canada and the United States recorded annual balances among their three most negative years on record. The geographical spread underlines the breadth of the losses.

Some regions dominated by smaller glaciers, including the Caucasus, Central Europe, and Western Canada and the United States, may already have reached "peak water," according to the report. This is the threshold at which runoff from glacier melt reaches its maximum. Beyond that point, continued ice loss raises the prospect of declining meltwater contributions as the remaining glacier becomes smaller.

The implications depend on local conditions and downstream reliance on glacier-fed water. The report does not establish a common timetable for every region, and annual ice loss cannot be translated directly into an equivalent reduction in usable supply. It does, however, expose the risk of treating water released by melting ice as evidence of a secure, lasting resource.

The largest human toll comes with gaps in the evidence

Asia and Africa accounted for at least half of recorded water-related extreme events and more than 80% of reported associated deaths over the past five years, according to WMO. Yet both remain among the least represented regions in the report's hydrological observations. Improving the evidence base is therefore closely connected to understanding risks where the reported human consequences are greatest.

Repeated disasters leave some communities little time to recover. Nigeria experienced major flooding for two consecutive years and the Democratic Republic of the Congo for three, the report says. For households, businesses and public authorities, such sequences raise questions about whether repairs and recovery can keep pace. Economic losses remain difficult to assess in many countries, limiting comparisons of the resulting burden.

The assessment also illustrates the need to distinguish the scale of a finding from the scale of a decision. Its global river-discharge estimates draw on 13 hydrological models driven by observed weather data, while groundwater findings concern monitored wells. These approaches reveal broad patterns, but local supply decisions require attention to coverage, uncertainty and the conditions of individual basins and aquifers.

Cross-border cooperation adds another dimension because upstream conditions can reshape water availability far downstream. WMO's call for shared data, common standards and coordinated early warnings reflects that interdependence. The next test of water security will be whether improvements in rainfall and river flows translate into sustained recovery of reserves, and whether countries can recognise the difference before another shortage arrives.