Global warming multiplies by four the intensity of torrential rains in Spain

As temperatures have risen in Spain due to global warming, the destructive rains have become stronger. In half a century, the intensity of torrential rainfall has multiplied by 4.5 times, according to a data collection carried out by the Polytechnic University of Catalonia.

The power and consequences of the torrential storms in Spain continue to illustrate the toll imposed by this phenomenon derived from the climate crisis. This week one person died and another is still missing, swept away by the water of a violent rain in the pareis torrent from Mallorca. Last March, Storm Nelson left four dead. It’s just the balance sheet so far in 2024. The trail of deaths from destructive storms can be traced from year to year. Just 12 months ago, in September 2023, another episode of torrential rainfall caused six deaths. The 2020 storm Gloria left 13 deaths in its wake. A very violent and very localized storm caused the loss of 13 lives in Mallorca in 2018.

“The analyzes show an increase in these extreme weather phenomena in the period we have studied,” say the UPC researchers. The increase is “significant” both for episodes of very heavy rain – with more than 30 mm of rain – and for those of torrential rain – 60 mm or more – which, according to these calculations, show “an increase in intensity of 360% since 1971.”

This work has specified the trends already described, for example, in the AEMET documents, which explain how the data “point to an increase in the frequency and intensification of situations that cause very heavy or torrential rains of significant extent in the whole of the Spanish Mediterranean”.

Heat influences

Precisely, the rain records of the half century studied by the UPC show that “very heavy rain episodes are relatively widespread throughout the peninsula and the Balearic Islands.” As for even more intense (torrential) rains, they have increased “in Andalusia, Castilla-La Mancha, the Region of Murcia, the Valencian Community, the south of Catalonia, the Balearic archipelago, Aragon, Navarra and the Basque Country.” The areas with the greatest intensity are concentrated especially on the Mediterranean coast.

In the context of global warming, researchers have sought the interaction between the escalation of temperatures in Spain and the pattern of precipitation. “The maximum measured temperature is the indicator that shows the greatest correlation for both total rainfall and droughts,” they conclude.

And in particular, they add: “In the case of extreme rainfall, the most powerful correlation occurs with the minimum temperature measured.” This means, they continue, that “the warmest years at night are those that show a stronger tendency towards extreme precipitation.”

The most significant thing is that we are experiencing a climatic paradox because there is going to be more and more drought, but with specific moments in which it rains, making it seem like the sky is going to fall.

Josep Roca
— Researcher at the Polytechnic University of Catalonia

Precisely the severe heat is triggering the nights with unprecedented temperatures due to how high they are. Tropical nights (with 20ºC) have become normal and the so-called torrid nights (+25ºC) have multiplied by six since 1980, according to the AEMET.

“The most significant thing is that we are experiencing a climatic paradox because there is going to be more and more drought, but with specific moments in which it rains, making it seem like the sky is going to fall,” says one of the authors of the study, Josep Roca.

Because the other side of the coin is that rainfall in general is scarcer in the peninsula and the Balearic Islands. In the same study period, a drop in total rainfall of 8.9% has been observed. This shift towards a drier Spain with higher temperatures is what has made this research team calculate that, at this rate, in just a couple of decades, the majority climate will become steppe rather than Mediterranean.

Without a change in the transformation trend, the typical Mediterranean climate would go from representing 24.43% of the peninsular and island territory in the reference period 1971-2000 to 10.13% in the period 2040-2060. A whole expansion of what they call “brown” Spain.