Flash floods are particularly dangerous and can carry away people, cars and damage property.

Where it occurs: Anywhere in the world where excess water can gather - in valleys or on flat ground near rivers, lakes, seas, etc.

Occurrences per year: 26 flood disasters recorded in the 1990s

Power: Six inches (15cm) of fast flowing water can knock a person off their feet, two feet (61cm) can carry a car away.

Casualties: 25,000 deaths per year

Flooding is an extreme natural disaster - it is estimated that around 1 billion people worldwide live under the threat of flooding. It can occur if a region experiences an unusually high amount of rainfall.

Rivers and lakes overflow and, as the ground becomes saturated, water builds up on the surface. Coastal areas hit by hurricanes, or tsunamis, can suffer flooding from the sea.

Flash floods - when heavy rain falls in a short amount of time - are particularly dangerous. In August 2004, the Cornish village of Boscastle in England was devastated by flash flooding - 50 vehicles were destroyed when two local rivers burst their banks, after 75mm of rain (half the average for the entire month) fell in just 2 hours.

Severe flooding can leave people without homes, power, or communications and, after the water, has subsided the survivors are left to face the threat of disease and starvation.