May 2025 was one of the driest Mays in decades. Due to a shortage of rainfall, high evaporation and low river discharge, problems are mounting for nature, agriculture and drinking water supplies. Recent showers and expected rainfall offer only temporary relief. Lasting recovery will require prolonged rainfall, according to Inge de Graaf and Lisanne Nauta of the Wageningen University & Research Earth Systems and Global Change Group.
May 2025 was one of the driest Mays in decades. Due to a shortage of rainfall, high evaporation and low river discharge, problems are mounting for nature, agriculture and drinking water supplies. Recent showers and expected rainfall offer only temporary relief. Lasting recovery will require prolonged rainfall, according to Inge de Graaf and Lisanne Nauta of the Wageningen University & Research Earth Systems and Global Change Group.
The water shortage has escalated at record speed. Up until mid-May, scarcely ten millimetres of rain had fallen regionally - well below the long-term average of around 60 mm. At the same time, four to five millimetres of water evaporated daily due to a combination of abundant sunshine, high temperatures and wind.
According to the KNMI (Royal Netherlands Meteorological Institute), May 2025 now ranks among the three driest months since records began. The current rainfall deficit stands at approximately 130 mm - more than double the average (40-50 mm). As such, this year is approaching the notorious drought record of 1976.
Low inflow
Inge de Graaf explains: "At Lobith, the Rhine is currently discharging only 1300-1700 m³/s - well below the long-term average of around 2000 m³/s, and even lower than during the dry May of 2018. In an extreme scenario, inflow could drop to 700 m³/s this summer. The Meuse is also discharging little, with only half of the usual volume."
The cause lies largely upstream in both river basins. In the Rhine basin - particularly Switzerland and southern Germany - there was exceptionally little snowfall this winter. Furthermore, the available meltwater was discharged early due to the warm and dry spring. Spring precipitation also remained well below normal there, leading to low soil moisture and limited runoff. The same applies to the Meuse basin in the Ardennes and northern France: little snow, limited rainfall, and highly dried-out soils.
New water inflow is not expected until substantial rainfall occurs later in June. However, current seasonal forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) and KNMI provide little cause for optimism: it appears likely to remain dry across much of the upstream areas.
Groundwater at critical levels
A fundamental problem is emerging underground: groundwater levels are "severely to extremely low" across large parts of the Netherlands (Figure 1). Only parts of South Limburg and the flanks of the push moraines show groundwater levels roughly average for this time of year. In these areas, the groundwater system responds more slowly, and the effects of the wet autumn and winter are still visible.
Shallow groundwater is especially vital: it feeds streams, ponds, nature reserves, and serves as a crucial reserve for agriculture and drinking water. Without replenishment from rainfall, this buffer disappears, directly affecting ecosystems, crops, and the availability of fresh water.
Recovery is slow. Even with significant rainfall, it takes weeks to months for water to infiltrate deeply enough to actually restore groundwater levels. The showers in late May and early June, as well as upcoming rainfall, will therefore provide only short-term relief.
What do the forecasts show?
Lisanne Nauta explains: "Our research group contributes to the ECMWF's long-term forecasts, focusing specifically on river discharges in Europe over the coming months. For May and June, the forecasts show that much of Europe will experience river flows below the long-term average (Figure 2). This applies particularly to the upstream areas of the Rhine and Meuse, where a dry winter, limited snowfall, and poor spring rainfall are resulting in sharply reduced inflows."
"In southern Europe - particularly Spain, Portugal and parts of Italy - we're seeing slightly higher flows, mainly due to localised and intense rainfall," Nauta adds. "However, these are regionally limited and do not compensate for the broader drought picture in central and northwestern Europe."
De Graaf adds: "The 'tercile-percentile' analysis, which compares the expected discharge to historical distributions, confirms that we are currently well below normal. While the models predict a slight improvement, there is no indication of structural recovery. The likelihood of a wetter turn remains small for the time being."
Outlook: little hope for recovery
According to De Graaf and Nauta, seasonal forecasts from KNMI and ECMWF provide little reason for optimism. On the contrary: the rainfall deficit is likely to increase further. The summer of 2025 risks being marked by persistent drought, an increased likelihood of heatwaves and rising temperatures. This means 2025 could end up even drier than the notorious drought year of 2018, which only developed later in the season.
Drought stress is already becoming visible in nature reserves: heathland is drying out, ponds are drying up rapidly, and groundwater-fed stream valleys are losing their supply. Concerns are also mounting in agriculture. Young crops are under pressure; in some places, water extraction bans are already in place. If the drought continues, crop damage will be unavoidable, with permanent yield losses as a result.
Water supply is also under pressure: around 60% of Dutch drinking water comes from groundwater. In parts of Brabant, Utrecht and Gelderland, extraction points are approaching critical levels. Water companies are taking precautionary measures and urging responsible use. In coastal areas, salinisation threatens as salty groundwater infiltrates the fresh water system.
Structural drought requires structural solutions
De Graaf: "What we are seeing is not merely a temporary rainfall deficit, but a symptom of structural drought under a changing climate. Our research group, working at the interface of hydrology, climate and adaptation, recognises a clear pattern: longer dry periods, faster evaporation, more extreme peaks, and simultaneous shortages in both groundwater and surface water."
The Dutch water system is not yet designed for this degree of drought and speed of change. According to De Graaf, more robust water management is needed: better water retention during wet periods, integration of groundwater and surface water in policy models, and adaptation strategies that take future extremes into account.
Inge de Graaf: "We are far from out of the danger zone. Now is the time to move from emergency measures to structural change in water management. Only in this way can the Netherlands become more resilient against tomorrow's droughts."
