Spain floods – why was the rain so intense?

Severe flooding in eastern Spain

Major flash floods have hit eastern parts of Spain, leaving scores dead and a trail of damage and destruction.

Chiva, just east of the city of Valencia, in the foothills of the mountains, had 491mm of rain in eight hours on Tuesday. That’s the amount of rain it would typically see in a whole year.

For some context, London’s annual rainfall is around 600mm. Imagine 80% of that falling in the length of an average working day, which is what has happened in eastern Spain.

Even in the region surrounding Valencia, 200-400mm of rain has fallen over a wide area. This huge volume of water has simply overwhelmed the rivers and drainage systems, leading to severe flooding.

What caused such intense rainfall?

As is often the case in situations like this, several factors – both meteorological and topographical – have come together to create the extreme rainfall.

In recent days, there has been a slow-moving area of low pressure across Iberia, which has created an unstable atmosphere in which severe thunderstorms have been able to develop.

With the low pressure being slow-moving, it has caused rounds of intense thunderstorms to affect the same places for hours on end.

Additionally, the wind has been pushing in a constant supply of warm, moist air off the warmer than average Mediterranean Sea. This has fed the thunderstorms with even more moisture, which has enhanced the torrential rainfall over land.

From a topographic perspective, there are steep mountains just to the east of Valencia – reaching as high as 1000 metres.

This causes warm, moist air at the surface to rise even higher into the atmosphere, which produces taller clouds that lead to greater rates of rainfall.

The mountains’ steep slopes also mean that when the rainfall reaches the ground, it is quickly concentrated and funnelled through the valleys below – creating raging torrents of water.

Climate change

Intense rainfall from thunderstorms is relatively common across the Mediterranean during the autumn months, due to seasonal changes that take place each year.

However, climate change is exacerbating extreme rainfall events like the one seen in Spain on Tuesday. A warmer atmosphere can hold more moisture, which in turn increases the intensity and amount of rain that is able to fall.

There’s no doubt that climate attribution scientists will be looking closely at the data and assessing how much of the extreme rainfall can be attributed to climate change.

A risk of further downpours

In the meantime, the slow-moving area of low pressure will continue to linger across Iberia in the coming days. This will lead to more heavy downpours across some parts of Spain – although probably not on the same scale as what happened on Tuesday.

Nevertheless, the Spanish weather service, AEMET, has issued a few amber and red warnings for some coastal areas of southern and eastern Spain, where flooding and other impacts are possible.

Meanwhile, the largely quiet weather here in the UK is set to continue well into next week for many, with no signs of stormy weather arriving on our shores anytime soon, and high pressure holding firm.