During the October 2025–February 2026 period analysed for the Iberian Peninsula, 84 of 151 days were under the influence of atmospheric rivers, according to a study published in Geophysical Research Letters. The research involved four investigators from scientific institutions in Spain and Portugal.
The study focused on the months of flooding and found that between 20 January and 15 February, seven of the nine major storms that hit Portugal were fed by atmospheric rivers. The storms named in the analysis were Ingrid, Joseph, Kristin, Leonardo, Marta, Nils and Oriana. Some of the depressions drew moisture from the same atmospheric river, while others had their own, making them larger and more dangerous. The destructive Kristin was associated with atmospheric river AR #2, while Leonardo was accompanied by a large subtropical atmospheric river.
In some regions of the Atlantic, the moisture transport from atmospheric rivers was more than 20% above the usual 1985–2014 values. The researchers compared some of these extreme episodes with near-catastrophic scenarios. According to the study, some current extreme atmospheric rivers showed characteristics comparable to simulations for the end of the century under a mean global warming of 4.4°C caused by greenhouse gases, a climate scenario known as SSP5-8.5. The study states that current extreme atmospheric rivers can generate moisture transport and hydrological impacts comparable to those projected in the early phases of high-emissions scenarios.
The successive episodes of extreme humidity had aggravated effects because they encountered increasingly saturated ground as they occurred, raising the risk of floods, landslides and land displacement, which ultimately happened. The moisture carried by the atmospheric rivers that reached Portugal originated mainly in the subtropical and tropical Atlantic. The researchers reconstructed the path of the water vapour up to ten days before it reached the peninsula.
Precipitation associated with atmospheric rivers was 8% to 12% higher in the north and centre of the country. Along the entire coastline, it was 10% to 20% higher than in the comparison made by the scientists. The study notes that anomalies in water vapour transport exceed 20% in extensive regions, referring to model results rather than concrete increases in rainfall compared with the previous year. In the actual count for those months by IPMA, February 2026 had 241.7 mm of average precipitation, or 329% of normal.
Atmospheric rivers are large corridors of humid air that travel between 2,000 and 4,000 kilometres, and can exceed 5,000 kilometres, from tropical zones to Europe. A large atmospheric river can transport 7 to 15 times the flow of the Mississippi River per second in water vapour, or 7.5 to 15 million tonnes of water. They are 400 to 600 kilometres wide, and most of the moisture is in the first two to three kilometres of altitude. That moisture turns into intense rain if the right conditions are present. An atmospheric river can pass over a region for 12 to 48 hours, sometimes longer.
Sources: Observador.