Floods are caused by a combination of factors and are mostly attributed to a piece of land's inability to quickly absorb large volumes of water. This is caused by dry soil, which in itself is a result of another extreme natural event, namely drought. Floods usually happen after a long period of time without rainfall, when the meteorological conditions line up for heavy rain or massive snow melts.

Over the past two decades, floods affected over two billion people around the world and those living in floodplains or vulnerable buildings were the ones who suffered the most. Floodings vary in intensity and can refer to large amounts of water covering land by just a few centimeters, enough to damage crop fields or homes, as well as to those that can cover almost entire buildings in water.

Floods happen almost all over the world every year and have increased in intensity over the past few years, with the most recent events in Europe taking place in Spain, where hundreds have perished due to flash floods.

How many types of floods exist

Given their intensity, not all floods are equal. Some can cause more damage than others and they also present different levels of risk for the population. Flash floods are usually the most dangerous types of flooding events, since they involve excessive rainfall that raises the water levels very quickly, which can't be absorbed by the soil. Narrow streets and highly-developed areas with a lot of asphalt and concrete, but little green space, are some of the most vulnerable spaces, since they don't provide sufficient absorption capabilities.

These were also some of the elements that led to the disaster that recently took place in Valencia and the region is still not completely out of the woods yet.

River floods are also a common type of flood caused by heavy rainfall or large amounts of snow melting, which results in a river exceeding its capacities. This mostly affects local communities found near the rivers and may not be as dangerous as flash floods, but occasionally, it can damage important local infrastructure, such as dams. This happened in China back in 1975 and we'll talk about some of the most disastrous floods in history.

Lastly, there are coastal floods, caused by storms that form around sea shores, such as cyclones or hurricanes, but they can also occur as a result of a tsunami. Experts at the World Health Organization say that between 80-90% of the natural disasters that happened in the last decade resulted from floods, droughts and severe storms.

Which areas are at high risk of floods

Generally speaking, experts say that densely populated areas are at the highest risk of flooding, because that's where people construct a lot of buildings and may not provide the surrounding are with sufficient green space, which acts like a sponge for large amounts of water. Mountain areas can also be a dangerous spot in case of flooding, especially if there's a river nearby, too.

Due to the land incline in these areas, rapid water runoffs can cause rivers to overshoot their capacity, leading to severe flash floods. To put things in perspective, a 15 centimeters-deep creek can turn into a 3 meters-deep fast river in less than an hour if a heavy thunderstorm stays over a specific area for enough time.

You can read more about other types of extreme weather phenomena in our other articles made on this subject that you can find here.

Recently-burnt areas are also a source of danger, since the soil has been damaged and doesn't have the capacity to absorb water anymore, even if there was vegetation in the area. After a flood, an area with healthy soil can benefit from the disaster, as the resulting mud is rich in nutrients and can be used by farmers as building ground for the next yields, although this doesn't make floods desirable by any means.

Additional risks may, in fact, come after the flooding happened. Receding water may continue to damage the structures that haven't been destroyed by the initial rush of water, while various contaminants may still be present. Petrol, pesticides and debris are just some of the hazards that remain after a disastrous flood. And let's not forget about the victims, which can sometimes be hard to reach and could slow the clean-up process. Cholera and hepatitis A are some of the diseases that commonly develop as a result of a flooding event.

Some of the world's most devastating floods

There have been many flooding events throughout the history of humanity, especially as these phenomena take place on an annual basis. One of the most devastating floods ever recorded is the Yellow River Flood, which occurred in 1887 in China. Despite happening 137 years ago, this remains one of the deadliest flooding accounts, as an estimated 900.000 to 2 million people perished. The heavy rainfall from September of that year caused the Yellow River, one of the world's largest, to raise up to 20 meters, destroying dams and other man-made structures, which ultimately led to the flooding of around 130.000 square kilometers.

Many farms were affected, towns buried under water and mud, which led to famine and disease outbreaks.

China's 1975 Banqiao Dam Failure is another mass-flooding event that hit the country almost 50 years ago and while nowhere nearly as deadly as the 1887 flood, it still claimed between 26.000-240.000 lives, damaging or destroying 61 dam structures. The flood was a result of Typhoon Nina and proved why it's important to build strong structures that can withstand the stress of one year's worth of rain falling in a single day.

Great Britain's 2007 floods were not as damaging as those in China by any measure, but they still prove why it's important to be prepared in case of such an event, even for a country that usually doesn't deal with this massive rainfall. It's true that the UK doesn't see the sun very often throughout a year and it rains quite a bit, but even so, the episode that took place 17 years ago was quite unusual. In June 2007, some areas in the UK received a month's worth of rainfall in just one day, while others, two times more than normally, not an unusually-high quantity. However, the soil wasn't prepared to take that in, resulting in floods that left 350.000 people without water, while also killing 13 people in total.

The costs associated with the disaster were estimated at 6.5 billion GBP and once again proved why it's important to take care of our infrastructure and maintain our drainage systems.

How do we protect ourselves from floods

As with any natural disaster, there are a few things you can do to make sure you stay as safe as possible in case of a flood, especially if you live in a flood-prone area. First off, when building a house in a flood-prone area, make sure that the actual building is elevated, no matter how little the elevation may be. Also, avoid displacing any electrical or important equipment between the ground and the base of the house. Make sure you build your home with flood-rated materials, especially at the base and don't skip on reinforcing it, if necessary.

Next, if you're caught outside your home during a flash flood, absolutely avoid ground or underground structures, such as stores and parking lots at any costs. Not only do they create strong water currents, but debris can also accumulate and travel at high speeds, presenting a great danger for your well-being.

Don't think you can walk or swim in flood water. Firstly, there may be currents waiting to pull you down, but most dangerously is what you can't see. Because floods bring debris and mud with it, nothing is visible, so it's like walking with your eyes closed. One fall is the only mistake you need to make, so don't make it and stay put. Find shelter at the higher levels, whether that be a shopping center or an exterior set of concrete stairs that are sturdy.

Don't drive either, as this is what causes a lot of fatalities during a flood. If your car is in an underground parking lot and you think about saving it, think of something else, because it's not worth risking your life for it. Chances are it's already flooded and will be declared totaled anyways by the insurance company.

If you need to leave your home, do so, but only if advised by the authorities. Before you go, don't forget to switch off the electricity, water and gas, as they can present a hazard of their own when you eventually return. If you have important items to store, put them in watertight compartments and move them as high as you can. Also, make sure to check on your neighbors, especially the elderly and vulnerable ones.

As floods are expected to get worse as a result of climate change, we have to make sure that we protect ourselves as best as we can from these extreme weather events. Building sustainable cities with plenty of green space that can absorb water and implementing anti-flood infrastructure is key, but also educating vulnerable population on what it should do in the case of such an emergency.