How floods progress

Floods can progress at different speeds:

Fast floods or flash floods 

These often occur in deserts where it rains in one place and the water starts to rush to an area further down stream, this could be tens or even hundreds of kilometres away.

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During fast flowing water floods, debris can also crash into other objects or collect on other objects producing large projectiles that can cause further damage.

Gradual floods

Some floods may take a few days to build up to dangerous levels. Others may take a few years.

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Slow floods can sometimes weaken the soil beneath structures and cause them to collapse.

What causes so much rain?

In some areas, floods are common because they are close to the equator and rainfall is very common. Other places are affected by monsoons, very heavy down pours at certain times of the year.

Another cause of long periods of rain are weather patterns like La Niña. This causes wetter weather during some years more than others.