The wettest winter in the last thirty years: what is happening?

BarcelonaThis winter's rains and snowfalls have been extraordinary, with very significant amounts and some records that have increased water reserves in the inland basins. above 90%In the last month alone, we've already been hit by six major storms, with varying degrees of impact on our country. The latest one, this week, was... LeonardoThe official list of names for storms in southwestern Europe is already halfway through the season. And to make matters worse, this is happening during what is usually one of the driest seasons of the year. Catalonia hasn't experienced such a rainy winter in thirty years, and February is still to come. Only the winters between 1995 and 1997 and some in the 1970s recorded similar figures.

But what exactly is going on? The reason lies in two key concepts: the polar vortex and the jet stream. The former is a large mass of very cold air located in the stratosphere that rotates around the North Pole. The latter is a current of strong winds that circulates through the troposphere at more northerly latitudes. It marks the boundary between the cold air of the poles and the warmer air of the tropics, and it's where storms usually move. This winter, the polar vortex has weakened, allowing cold air to descend further south, and the jet stream has shifted to lower latitudes. All of this has directly affected us.

"We've had an anomalous situation for many weeks, causing storms to circulate at lower latitudes; it's infrequent, not exceptional, but it's causing an unstable and very rainy winter in our country, when this time of year is usually dry," Marc Prohom explained to ARA. The rainy trend could continue into spring.

This situation goes against all future forecasts, which predict less rain in our country in the coming years. In fact, December has been the month that, in recent years, has shown the driest trend, with a clear decrease in precipitation. This year, however, the second half of December has been rainy; the easterly winds during Christmas week are particularly noteworthy.

"Climate change projections indicate the opposite of what we are experiencing this year: increasingly dry and anticyclonic winters, just as has happened in recent years," says Prohom. "If the situation we are experiencing were a film, this winter's phenomenon would be a single frame that certainly wouldn't represent the film as a whole," he adds. The most recent precedent for abundant winter rainfall is Storm [name of storm missing]. Glory January 2020. But that episode lasted five days, whereas this winter rains have been frequent all season.

Record rainfall under the shadow of the climate crisis

The rains have also broken some precipitation records. According to the recent climate report from Meteocat, weather stations with data dating back to 1950, such as Palafrugell (Baix Empordà) and Granollers (Vallès Oriental), have recorded their wettest December and January periods in these 76 years of records, with 368 and 308 l/m², respectively. The city of Girona, with 442 l/m², and Cabanes (Alt Empordà), with 411 l/m², have recorded their second wettest winter period since data collection began in the mid-20th century. Many other weather stations are also experiencing one of their wettest winters, often with precipitation more than 200% or 300% above the average.

This situation has also led to record winter rainfall at several Meteocat stations with shorter data records – between 30 and 36 years – especially in the Empordà region and parts of Lleida. Furthermore, the Ebro Observatory and the Fabra Observatory in Barcelona, ​​with over 100 years of data, have already recorded their fourth and fifth wettest winters this year, with 263 and 230 l/m², respectively. And the Pyrenees hadn't seen this much snow in decades, with accumulations of between two and three meters at higher elevations. "These record-breaking rains could be linked to global warming and the atmosphere's increased capacity to retain moisture. With conditions favorable to storms, like the recent updrafts, rainfall accumulation can be higher than what we were used to in previous years," he concludes.