By Joanna Robinsonweather producer

The floods in Spain have been difficult to witness, but the rains there could never have been anything other than devastating.

Chiva, located just west of Valencia, received 491 mm of rain in an eight-hour period; Between 100 and 200 mm fell in the surrounding areas, and the accumulation of running water produced apocalyptic scenes.

In addition, more than 20,000 lightning strikes have occurred.

While the rainfall totals are amazing in themselves, this part of the world is simply not used to large amounts of water falling from the sky.

In an average year, Spain would expect between 50 and 100 mm of rain throughout the month of October, but Valencia and Andalusia would expect much less: only 60-70 mm.

So how did this happen?

It is attributable to a DANA, an ‘isolated depression at high levels’ or a ‘cut-off low’.

This is a low pressure system that becomes sluggish or stationary, blocked by high pressure elsewhere, which can only continue to pour rain over the same area for long periods of time.

These systems are not that unusual.

It’s not unusual, but this one was different.

They occur when cool air from the north crosses the Mediterranean in late summer and autumn, when the waters are warm.

The temperature differential increases storms and precipitation totals.

While not uncommon, this one was certainly extreme. And it’s not gone yet.

This same system has continued to bring heavy rain and thunderstorms today, but has now moved a little further north and east, heading towards the French border and currently remaining west of Barcelona.

Rain and storms are likely to continue for some days, with the regions of Tarragona and Castellón still under an amber warning, while a yellow warning remains in force for both eastern and western Spain.