Valencia floods: Our warming climate is making once-rare weather more common, and more destructive
In the last few days, a seasonal weather system known in Spain as the “cold drop” or DANA (an acronym of depresión aislada en niveles altos: isolated depression at high levels) has caused heavy rain and flooding across Spain’s Mediterranean coast and in Andalusia, especially in the Valencian Community, Castilla-La Mancha and the Balearic Islands. The storm has left hundreds dead and many more missing, with immense damage in the affected areas.
50 years ago, a DANA occurred every three or four years, typically in November. Today, they can happen all year round.
How does a DANA form?
These storms are formed in the same way as Atlantic hurricanes or typhoons in China. The difference is that the Mediterranean is smaller than these areas, and so storms have a shorter path, and store less energy and water vapour.
Decades ago, warm sea surfaces at the end of summer would cause water to evaporate into the atmosphere. Today, the sea surface is warm all year, constantly sending massive amounts of water vapour up into the atmosphere.
The poles are also much warmer now than they were 50 years ago. As a result, the polar jet stream – the air current that surrounds the Earth at about 11,000 metres above sea level – is weakened and, like any slowly flowing current, has meanders. These bring cold air, usually from Greenland, into the high atmosphere over Spain.
The evaporated water rising off the sea meets this very cold air and condenses. The Earth’s rotation causes the rising air to rotate counterclockwise, and the resulting condensation releases huge quantities of water.
This combination of factors causes torrential, concentrated rains to fall on Spain, specifically on the Balearic Islands and the Mediterranean coast, sometimes reaching as far inland as the Sierra de Segura mountains in Andalucia and the Serrania de Cuenca mountains in Castilla la Mancha and Aragón. These storms can move in very fast, and are extremely violent.
On occasions, this Mediterranean water vapour has moved as far as the Alps, crossing its western point and causing downpours in Central Europe.
Warming oceans, warming poles
Many years ago, humans discovered a gigantic source of energy: 30 million years worth of the sun’s energy, stored under the ground by plants and animals. Today, we are burning through this resource fast.
This fossilised energy source is made up of carbon compounds: coal, hydrocarbons and natural gas. By burning them, we release polyatomic molecules such as carbon dioxide, methane, nitrogen oxides and other compounds. Once released into the atmosphere, these trap some of the heat radiating from the earth’s soil and seas, returning it to the planet’s surface.
This process is what causes climate change, and it can occur naturally. When these molecules, especially methane, are stored in continental ocean slopes, the water cools and the carbon dioxide captured by the waves is trapped inside. As the planet cools and sea levels fall, methane is eventually released into the atmosphere. The atmosphere warms up, warming the sea, and the sea releases CO₂ which amplifies the effect of the methane. The planet then gets warmer and warmer, causing glaciers to melt and sea levels to rise.
This alternation of cold and hot has occurred eight times over the last million years.
No end in sight for fossil fuels
Today we are forcing this process by emitting huge quantities of polyatomic gases ourselves. The question is whether we can limit these emissions. So far, this has been impossible.
To this we can add the fact that by 2050 there will be about two billion more human beings on the planet, who will also need food, housing and transport. This means more chemical fertilisers, cement, petrol, diesel and natural gas will be consumed, leading to further polyatomic gases being released.
Various measures to limit the burning of carbon compounds are falling short, or developing very slowly. Hopes for electric cars, for example, have been greatly diminished in recent years.
In Europe progress is being made in solar and wind energy, but electricity only makes up around a third of the energy consumed. Europe is also the only region making real progress on alternative electricity generation – much of China’s progress is being offset by its continued construction of coal-fired power plants.
Despite some large, high-profile projects, the reality is that we will continue to burn carbon compounds for many decades to come. This means the concentration of polyatomic gases in the atmosphere will increase over the next century, and with it the temperature of the planet, leading to more DANAs, hurricanes, typhoons and floods.
Climate adaptation is vital
What we are left with is adaptation, which is much more manageable as it does not require international agreements.
In Spain, for instance, we can control flooding through massive reforestation in inland mountainous areas, and through rainwater harvesting systems – building small wetlands or reservoirs on hillsides. This would slow the amount of water reaching the ramblas and barrancos, the gorges and channels that funnel rainwater through Spain’s towns and prevent them from flooding. At the same time, this would mean water can be captured by the soil, where it can then be gradually returned to the rivers and reservoirs.
Not only is this feasible, it is cost-effective, generates many jobs, and could save hundreds, if not thousands of lives.
