What Causes Floods?

From single buildings to entire communities, floods can wreak havoc - causing thousands of pounds worth of damage and potentially endangering lives in the process. Even in the UK, where our climate is regarded as less ‘extreme’ than other tropical countries, we still spend an extortionate amount of money on flood defences. Between 2008 and 2011, that figure hit £2.37billion.

To mitigate the effects of flooding, we need to have a sound understanding of what actually causes floods. Armed with this knowledge, we can take steps to prevent devastation, whether via physical barriers or a change in planning legislation.

So what causes floods, exactly?

1. Extreme Weather

The most widely-known cause of flooding is, of course, extreme weather. Heavy rainfall is most commonly associated with the potential for flooding - whether that’s river floods, groundwater floods, or flash flooding. Rain is not the only culprit. Ice and snow can cause flooding when they melt, and strong winds in coastal areas can cause flooding from high tides and freak waves.

As time goes on, climate change may impact the extremity of weather in the UK and indeed across the globe. Along with this unpredictability comes the potential for flooding.

2. Natural Disasters

From time to time, the world is hit with a natural disaster that causes widespread devastation, loss of life, and flooding. A very direct example is a tsunami; none of us can forget the destructive power of water displayed by the Indian Ocean tsunami in 2004, and then again on the coast of Japan in 2011.

It’s not just tsunamis that can cause flooding; hurricanes can cause deadly inland floods, too. In 2005, 67% of deaths caused by Hurricane Katrina were directly caused by flooding, whether via drowning, due to the physical impact of debris or through exposure.

3. Overdevelopment

If land is overdeveloped with buildings and roads, rain water cannot penetrate into the soil - causing flooding. In some areas, this is compounded by building developments on floodplains; areas of low-lying land that is flat, accessible and easy to build on. But these areas are at a high risk from flooding, often because they are in close proximity to a body of water that could burst its banks during extreme weather events. If a floodplain is overdeveloped, rainwater has nowhere to go; which means man-made drainage is vital. 

4. Deforestation

Large forested areas help to prevent flooding by soaking up excess water into the soil. In areas of large-scale deforestation, the soil is unable to act as a ‘sponge’: instead, it is often washed away by rainwater and floods follow. Countries such as China have experienced first-hand how deforestation can cause widespread and destructive flooding.

5. Defence Failure

By understanding the causes of flood, we can build defences such as seawalls, barriers and dams. But these are not always fool proof, and if there is a failure in defence systems this could cause unexpected flooding. A continued analysis of the causes of flooding is necessary to protect our homes and livelihoods, especially as climate change continues to unfold.

If you, like many, think that the number of floods is increasing, read this article: Are There More Flood Now? You may be surprised by what you find out.