European river flows drop to 30-year low as Western Europe records warmest summer

Depleted river discharge and infrastructure strain

European river systems recorded their lowest average summer discharge since systematic records began in 1992, according to an assessment released from Bonn by the European Union Copernicus Climate Change Service. Water volume deficits became acute during July and August, when several large rivers across the continent registered record or near-record low flows. These depleted river channels included the Rhine, Danube, Po, Loire, Rhône, and Seine. The low river volumes created operational difficulties across multiple sectors, reducing the availability of freshwater for agricultural irrigation and municipal supply networks. The reduced water volumes also constrained hydroelectric power generation and limited cooling capacity for nuclear power reactors. Copernicus representatives stated that these widespread water shortages showed the direct connection between climate change and broader geopolitical challenges, including continental energy security.

Marine heatwaves across European seas

Alongside depleted inland river systems, marine environments surrounding the European continent experienced elevated surface temperatures throughout the summer months. Sea surface temperatures reached record or near-record levels across broad sections of the Atlantic coastline and throughout the western and central Mediterranean Sea. These elevated water temperatures produced marine heatwaves that researchers classified from strong to exceptional in intensity. Copernicus analysts observed that these warm waters had direct consequences for nearby land environments by altering coastal atmospheric conditions and preventing nocturnal relief.

Marine heatwaves can amplify heat in adjacent coastal areas by limiting nighttime cooling and increasing humidity, worsening heat stress.

Record heat across Western Europe

Continental temperature records confirmed that the season was the warmest summer on record for Western Europe and the third warmest across the European continent as a whole. Western Europe recorded an average seasonal temperature of 21.7 degrees Celsius, which stood 2.5 degrees Celsius above the baseline average measured between 1991 and 2020. The intense conditions generated widespread thermal discomfort across vast populated areas. By the conclusion of the summer season, a record 52% of the European land surface was exposed to heat stress categorized as very strong. This classification corresponds directly to perceived temperatures reaching 38 degrees Celsius or higher.

Heatwave duration and wildfire expansion

The seasonal assessment reported that the summer was defined by both the geographic extent and the prolonged duration of extreme heat. Western Europe experienced 17 separate days during which at least 60% of its land area registered temperatures exceeding 30 degrees Celsius. This duration exceeded previous hot summers, comparing with 11 such days during the 2003 heatwave and 7 days recorded across the region in 2025. The combination of persistent drought and repeated heat spells also produced an intensive wildfire season across the European Union. By 2 September, the total land area burned by wildfires in the EU was almost twice as large as the multi-year average recorded between 2006 and 2025.