Natural Hazards: Flood Mitigation

Best practice

Background

Floods are the most frequently occurring natural disaster, causing widespread devastation, resulting in destruction of property, business interruption and loss of life.
The associated impacts of climate change will likely result in an increase in both the frequency and severity of flood events across the globe.

Floods can severely impact businesses, disrupting operations and damaging property. However, businesses can take action to significantly reduce their impact, through preparation and mitigative action tailored to the specific exposures, improving resilience to these events.
 

Understanding Types of Floods

Exposures can vary based on the type of flood event, which is why it is important to understand the differing impacts each can have:

  • Fluvial Flooding is flooding from a water body such as a river or lake, where the water level rises, exceeding the capacity of the water body and causing it to overflow onto neighbouring land. The severity of these floods is influenced by the topography of the location and the intensity of the increase in the volume of water.
     
  • Pluvial Flooding is flooding from a severe rainfall event, also known as flash flooding or surface water flooding. Flash flooding can be intensified when a large volume of water occurs in proximity to elevated terrain but can also occur when a large volume of water is released from an upstream location such as a dam. Flash floods generally result in a large volume of water moving with force, causing property destruction and moving debris. Surface water floods tend to occur when localized drainage systems become overwhelmed, causing water to ingress into property and urban areas.
     
  • Storm Surge is flooding due to a rise in sea level caused by a natural catastrophe such as windstorm events (typhoon or hurricane). The severity of damage caused by storm surge is influenced by the intensity and direction of the storm, the onshore and offshore topography and the adequacy of sea defenses.

As temperatures increase this will cause more water to evaporate from the land and oceans, and changes in the frequency and magnitude of heavy precipitation events may in turn affect the frequency and magnitude of river flooding. (#1)

Cost of Damage (2025)

Each year, floods destroy assets worth significant amount of money. 

Between 2020 and 2024, losses from flooding across the globe amounted to US$325bn, of which only US$71bn was insured. (#2)

Time to Adapt & Act

  • Uncertainty on flood risk is increasing with climate change. Main uncertainties arise from level of damage, frequency of events and where events will happen.
  • Mitigation is now more important than ever when it comes to flood risk management. The investment in mitigation will be compensated by long term resilience.
  • Property damage caused by flooding is at an all time high. Flooding also is causing significant business interruption costs and supply chain disruption.
  • Always seek professional advice on how to protect your assets & people. Risk Engineers have the expertise & experience to help you become resilient to flood.

Major Flooding Events

Major Flooding Events


11 General Risk Management Suggestions

Quick & Easy Fixes

Ensure your emergency response plan is relevant, up to date, appropriate for your facility and exercised at least annually before any wet season.

Ensure all critical equipment, expensive stock and contents are located on upper floors. It is often the case that basements, at high risk of flooding, are traditionally used to house such items.

Ensure that employees know what to do before, during and after any flood event. All areas of the emergency response plan should be known, implemented, and followed with roles and responsibilities clearly allocated.

Make sure all drainage systems are in working order, designed correctly, and are clear of any debris that could prevent water flow.

Make sure yard storage / external equipment is limited around your premises as certain items can cause floating debris, which could penetrate building façades (such as glass).

Be aware of external sloping and the topography of your locations. Even with small flooding events, the topography can materially increase / decrease your flood risk. Understand any potential weak points and mitigate the risk.


Mid to Long Term Solutions

A well designed flood protection system should be considered to protect your assets. It is important the system is designed to protect your risk and is maintained effectively.

Occasionally inspect and check that all local protection systems are in good order. For example, a local river which has overgrown vegetation or foreign objects present could cause a backup of water. Consult with local authorities if you identify any issues.

Any openings to your facility or property should be raised to an acceptable level to reduce the risk of water entering the premises. This would go for any external plant rooms, which may be detached from the main premises.

Ensure any underground tanks, such as fuel reserves, are adequately sealed from water penetration according to the manufacturer’s guidelines.

Due to climate change, flooding events are now occurring in areas which have never flooded before. Ensure mitigation is a top priority regardless of previous events. Utilize climate modelling analytics to understand the risk in better detail.


Main Technical Reference Documents

(#1) Climate Change Indicators: River Flooding - United States Environmental Protection Agency. (2016)
(#2) Flood risks on the rise - Greater loss prevention is needed | Munich Re.
(#3) – WMO - Devastating rainfall hits Spain in yet another flood-related disaster
(#4) – Queensland Reconstruction Authority / Deloitte Access Economics (June 2022)
(#5) – NHESS - A multi-disciplinary analysis of the exceptional flood event of July 2021
in central Europe
(#6) – China’s Unrelenting Season of Flooding: Earth Observatory
(#7) – Thailand Flood 2011 - One Year Retrospective – Guy Carpenter

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