Disaster in Valencia: A Signal of Climate Change

A disastrous weather event struck Valencia between October 29 and 31, 2024, bringing record rainfall, flooding, and devastating landslides. According to Spain’s national weather agency, Aemet, on October 29, 2024, areas like Chiva recorded over 490 liters of rain per square meter in a single day, amounts the region typically sees in an entire year.
The floods have so far resulted in 207 confirmed deaths, 1,900 people reported missing, and hundreds of injuries. The region’s infrastructure suffered severe damage: more than 60 roads were closed, rail transportation was disrupted, and the Port of Valencia was shut down. The estimated cost to rebuild infrastructure, restore essential services, and support the displaced is currently over 2 billion euros.

Credits: US Landsat-8 satellite

What Caused the Floods in Spain?

The recent flood in Spain was triggered by a weather event known as DANA (Depresión Aislada en Niveles Altos or Isolated High-Altitude Depression), also known as gota fría or “cold drop.” This phenomenon occurs when a mass of cold air detaches from the jet stream and moves over warm waters. The strong temperature difference rapidly lifts warm, humid air from the sea surface, forming storm cells capable of unleashing torrential rains. In October 2024, western Mediterranean temperatures exceeded 26°C, abnormally high for the season, creating the ideal conditions for an intense gota fría.

The Impact of Greenhouse Gases on Ocean Warming

From 1880 to today, the average surface temperature of the oceans has risen by about 1.5°C, with a sharp acceleration over the past 50 years. According to the National Oceanic and Atmospheric Administration (NOAA), 2023 set a new record, with the average surface temperature of the oceans reaching 21.1°C. Western Mediterranean sea temperatures, in particular, have recorded summer peaks above 30°C in recent years, averaging 4-5°C above seasonal norms. This anomaly provides extra energy to storms, intensifying them.

Credits: ESA (Data: E.U. Copernicus marine service International)

This is mainly due to the accumulation of greenhouse gases (GHG) in the atmosphere, such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), which trap solar heat and prevent its dispersion into space. This phenomenon, known as the greenhouse effect, causes the entire Earth’s climate system, including the oceans, to warm:

• CO₂ has risen to 420 ppm from 280 ppm pre-industrial levels.
• Methane (CH₄) is now around 1,900 ppb and is 25 times more potent than CO₂.
• Nitrous oxide (N₂O), at 335 ppb, is 298 times more potent than CO₂.

These gases trap heat, much of which is absorbed by the oceans:

• Oceans absorb over 90% of this heat
• Absorb up to 30% of CO₂ yearly.

Credits: NOAA-GML; Friedlingstein et al 2023; Canadell et al 2021 (IPCC AR6 WG1 Chapter 5); Global Carbon Project 2023

As water temperature rises, more evaporation occurs, increasing the humidity in the air above the sea surface. Studies show that for each degree of water temperature increase, the atmosphere can hold about 7% more water vapor. This increase makes storms and weather disasters like DANA much more intense, as the storm cells formed above the Mediterranean carry a greater-than-normal volume of water, thus amplifying rainfall and flood risks.

Global temperature rise not only increases the intensity of weather events but also multiplies their frequency. According to the IPCC (Intergovernmental Panel on Climate Change), events that once occurred only once every 10 years are becoming more common. With the increase in global average temperature of 1°C above pre-industrial levels, the frequency of such events has risen up to 2.8 times per decade. At the current pace, if warming reaches 2°C, the frequency of extreme events could increase up to 5.6 times every 10 years. This means that devastating events, once considered rare, could become recurrent, with unsustainable human and economic costs.

Acting Now to Avoid the Worst: The Need to Reduce GHG Emissions

If we do not act quickly to mitigate climate change, extreme events like DANA will become increasingly frequent and destructive, profoundly transforming life as we know it. For example, the recent flood in Valencia demonstrates how global warming, fueled by greenhouse gases, intensifies storms, making meteorological phenomena that were once rare more common today. In the face of these escalating disasters, local and national governments will face growing financial strains, which will hinder their ability to rebuild and provide timely assistance. Besides the immediate costs, there are lasting impacts on quality of life.

Moreover, if climate change continues unchecked, extreme events will disrupt access to essential resources such as drinking water and food, destabilizing critical sectors like agriculture and tourism. Consequently, this will lead to a decline in our standard of living, increasing community vulnerability and threatening economic stability. Thus, taking action now is crucial to preserve a livable and safe environment.

Reducing greenhouse gas emissions and adopting climate change adaptation strategies are not only necessary to prevent loss of life and economic disaster. They are also the only way to ensure a sustainable and dignified future for the generations to come.