The catastrophic floods in Spain on October 29 and 30, 2024 — already attributed to global warming and consequent climate change — spread to other parts of the country on November 2 and 3 following torrential rainfall.
In one of Europe’s worst weather-related disasters, the floods have killed over 200 people, with many still missing. According to Spain’s Interior Minister, a reliable estimate of the exact number of missing people cannot yet be given. Rescue and relief operations are ongoing, even as the region continues to receive heavy rainfall.
The death toll from the floods is the highest in Europe since 1967, according to the news broadcaster BBC.
Several locations in the southeastern and northeastern provinces, including Alicante, Murcia, Almeria and Barcelona, experienced extremely heavy rainfall and subsequent flooding since November 1. Rain fell incessantly in some areas, particularly in Barcelona, on November 4.
The town of Chiva and the city of Valencia have faced the most severe rainfall and flooding.
A weather station in Chiva recorded 491 millimetres of rainfall in just eight hours on the night of October 29-30, equivalent to a year’s worth of rain, according to Agencia Estatal de Meteorología (AEMET), Spain’s meteorological agency.
Overall, Chiva received more rain on October 29 than in the past 20 months, according to television network The Weather Channel (TWC). “Water overflowed a gully that crosses the town, tearing up roads and walls of houses,” TWC reported on its website.
The destruction in Valencia is evident from before-and-after satellite images, which reveal the transformation of the Mediterranean city into a landscape inundated with muddy waters. “The V-33 highway was completely covered in a thick layer of mud,” TWC added.
The extreme rainfall in Spain is linked to a series of intense thunderstorms caused by an isolated depression at high altitudes, commonly known in Spain as a depresión aislada en niveles altos or DANA storm.
Earlier, Down To Earth reported that the storm’s intensity was amplified by excess moisture accumulating over a small area in eastern Spain due to a blocking pattern in the upper atmosphere.
A DANA storm occurs when a low-pressure region becomes isolated from the subtropical jet stream in the upper atmosphere, creating a “cut-off low” system.
This phenomenon often occurs in autumn when the remaining surface heat from summer meets a sudden influx of cold air from polar regions, according to the World Meteorological Organisation (WMO).
“This leads to what meteorologists used to call “a cut-off system” with low-pressure values that persist over a few days and rotate over the region concerned,” the WMO stated.
At the surface, these systems generate easterly winds that bring warm, moist air inland from the Mediterranean Sea, wrote the World Weather Attribution in its rapid attribution study on the Spanish Floods. “This air is then forced upward along the complex terrain of eastern Spain, leading to significant rainfall along the coast and often triggering flash floods, locally termed riadas,” it said.
“The presence of warm air near the surface being fueled by excessive moisture from the still-warm Mediterranean Sea and the instability generated by the conflict with cold air in the upper atmosphere leads to large convective clouds with heavy downpours and sudden flash floods,” said Omar Baddour, chief of Climate Monitoring at WMO.
The WWA analysed three observed rainfall datasets from the region and found that rains were 12 per cent more intense and twice as likely in a world 1.3 degrees Celsius warmer than the pre-industrial era. A one-day rainfall event over eastern Spain now has a 20-year recurrence, according to one of the datasets.
However, the WWA cautioned that this was not the true picture as “it is important to note that this does not represent the heaviest rainfall in certain regions that caused devastating floods, like Chiva, which received more than 400 litres per square metre in less than 24 hours. This analysis thus serves as a first estimate of the role of human-induced climate change.”
“The results are based on daily rainfall extremes. Many flash floods are driven by extreme rainfall on shorter, sub-daily timescales, of only a few hours,” said the WWA. “Studies have shown that the intensity of sub-daily events is showing stronger increases driven by human-caused climate change than daily rainfall extremes, globally by about 20 per cent.”