Floods: What are the causes and what to do when they occur?

Since the start of the year, floods have wreaked havoc and displaced thousands of people in countries around the world.

Studies show that heavy rainfall is becoming more frequent and severe in many parts of the world due to climate change, and experts have warned that this trend is likely to continue.

Afghanistan, Brazil, Indonesia, Kenya, Oman and the United Arab Emirates are just some of the countries affected by heavy flooding so far in 2024.

Each time, rising waters caused massive destruction and left thousands of people homeless.

Here we look at the causes of flooding, why they are becoming more common, and what you can do to help yourself and others when flooding occurs.

Floods, the most common type of natural disaster, occur when water overflows and submerges dry land.

Flooding can occur throughout the year, but climate change is intensifying rainfall, increasing the risk of flooding.

Flooding that occurs after periods of heatwaves and prolonged hot, dry weather can be particularly damaging.

“This means that the ground is very hard and dry. When heavy downpours hit parched soil, rainwater is absorbed much more slowly. The water can ‘stay’ on the surface. This can lead to runoff of surface, which can cause flooding,” explains the British Red Cross.

Flooding can cause widespread devastation, resulting in loss of life as well as damage to personal property and critical public health infrastructure.

According to the United Nations (UN), between 1998 and 2017, floods affected more than two billion people worldwide.

The people most vulnerable to flooding are those who live in floodplains and those who live in makeshift or poorly constructed structures. Communities that lack warning systems or have little awareness of flood risks may also be affected, the UN adds.

Floods can be triggered by heavy rains, rapid snowmelt or storm surges from tropical cyclones or tsunamis in coastal areas.

There are three types of flooding:

• Flash floods occur when rapid, excessive rainfall causes water levels to rise quickly, overwhelming rivers, streams, other water channels, or roads.
• River flooding occurs when heavy, consistent rain or melting snow causes a river to exceed its capacity.
• Coastal flooding is triggered by storm surges from tropical cyclones and tsunamis.

According to the United Nations, 80 to 90% of natural disasters recorded over the past ten years have been caused by floods, droughts, tropical cyclones, heat waves and violent storms.

Floods destroy homes, disrupt transportation and ruin businesses.

People whose homes, businesses or communities have been flooded may need help for days, months or even years, the British Red Cross says.

“It only takes 15 centimeters of rapidly flowing water to knock over a person, and 61 centimeters of water to float a car.

Additionally, flooding can overload sewers and contaminate water, spreading disease.

“Floods can leave people in need of food, shelter, medicine, clothing and money. Some may need help returning to work and transportation to get there.”

Even for those lucky enough to have insurance, it can be difficult to make a claim after the event. Often, insurers will no longer insure a home after a series of floods, or premiums will be higher.

According to the Association of British Insurers (ABI), getting home after a flood can take “a year or more”. In May, a BBC report showed that almost 100 flood-affected businesses were still awaiting compensation payments more than six months after the major floods hit Northern Ireland.

In many parts of the world, those affected have no insurance.

Many rivers meander gently as they gradually descend towards the sea. So when a river is in flood it usually happens slowly as it takes some time for the rain to seep into the ground and flow into the rivers and towards the sea, which leaves a little time to prepare.

In contrast, in the case of a flash flood, there is often very little time between the start of precipitation and the appearance of flooding.

“Flash floods are more common when rivers are narrow and steep, making them flow faster. They can also originate from small rivers in built-up urban areas, where hard surfaces such as roads and concrete do not “do not allow water to flow into the ground,” explains the Met Office, the United Kingdom’s national weather service.

“This leads to surface overflows and can often overwhelm local drainage systems, causing flash flooding.”

Trees, green spaces and plantations are all ways to absorb water and mitigate the effects of flooding in cities.

According to experts, here’s what to do in case of flooding:

• If there is a threat to personal safety, call emergency services immediately.
• It only takes 15 centimeters (6 inches) of fast-moving water to sweep you away, and 61 centimeters (2 feet) to sweep away a car.
• Do not walk on dykes or river banks.
• Avoid contact with flood waters. They can be contaminated by wastewater. If you are exposed, wash your hands and clothing thoroughly with clean water.

According to the United Nations, “the frequency and intensity of extreme precipitation events are expected to continue to increase due to climate change.”

As the planet warms, the air can hold more moisture – about 7% more for every 1°C increase in temperature. This can result in more droplets and heavier precipitation, sometimes in a shorter period of time and over a smaller area.

“Warm air can hold more moisture. If the air has an unlimited supply of water, like an ocean, the warm air absorbs more moisture. Clouds then contain a greater number of droplets of larger amounts of rain, which explains why showers are often heavier in summer than in winter,” explains the Met Office.

“As the climate continues to warm, this effect will become more pronounced and heavy precipitation is expected to become more frequent.”

Scientists are assessing whether extreme weather events can be attributed to climate change, taking into account natural and human causes.

In the case of the intense rains that fell on Dubai, the United Arab Emirates (UAE) and Oman in April 2024, it is difficult to determine precisely the significance of the role played by climate change.

Indeed, heavy rains are rare in this region, which limits historical comparisons for scientists.

However, precipitation of this type has become 10 to 40 percent more abundant, and climate change is the most likely explanation, according to the World Weather Attribution (WWA) group.

“If humans continue to burn oil, gas and coal, the climate will continue to warm, precipitation will continue to be heavier and people will continue to lose their lives in floods,” says Friederike Otto, master of lectures in climate science at Imperial College London.

April was also marked by extreme flooding in parts of East Africa. Scientists are racing to study the exact role of climate change.

In September 2023, northern Libya was hit by deadly floods. According to WWA, the impact of climate change has increased the probability of heavy precipitation by 50 times. Additionally, years of political instability have left the region’s residents ill-prepared for such dramatic events.

According to the IPCC, the United Nations body responsible for climate issues, heavy precipitation has become more frequent and more intense over most land areas due to human activity. This phenomenon will continue with continued warming, the IPCC has warned.