A flood risk assessment (FRA) is a study that looks at the chance of flooding from all possible causes. It finds ways to reduce flood risks and gives advice on what to do before and during a flood. Floods can come from different water sources, such as groundwater, surface water (like rivers or streams), artificial water (such as broken water pipes, canals, or reservoirs), sewers, drains, and seawater.
Each water source can cause floods in different ways. For example, high groundwater and poor drainage systems can both lead to flooding at the same time. The shape of the land, the type of soil, and the features of buildings or planned areas must be studied. A flood risk assessment should check how likely a flood is, what effects it might have, and how vulnerable an area is.
In the United Kingdom, professional flood risk assessments are done by civil engineering experts. These experts are members of the Institution of Civil Engineers and follow strict rules. They must stay fair and not be influenced by any group. Their advice is protected by insurance through companies like Lloyd's of London.
Flood risk assessments can cover one building or a large area. They may be used to check flood risks for homes or businesses or to provide proof for planning projects in England and Wales.
In the United States, flood maps are made by the Federal Emergency Management Agency (FEMA). FEMA works with local governments to find areas at risk of flooding. A process called Risk MAP helps create Flood Insurance Rate Maps. These maps show how communities can prepare for floods and are divided into four steps: Discovery, Analysis & Mapping, Preliminary Flood Mapping Release, and Map Adoption. The goal is to find flood risks, share information, and help reduce dangers.
Local governments use these maps to tell people where to go if they need to leave quickly and how to read flood zones.
Flood watches and warnings let people know if their area might flood or will flood during a certain time. These updates are managed by the National Weather Service, which shares flood information daily on its websites. Cars are the most common cause of deaths during floods. Many people think their vehicles can handle water on roads, but they don’t know what is under the water or if the road is safe. Water can rise quickly, and being in a car during a flood is very dangerous. If you see floodwater, leave the area as soon as possible.
England and Wales
In England and Wales, the Environment Agency and Natural Resources Wales each require a professional Flood Risk Assessment (FRA) to be included with planning applications for areas that are at risk of flooding (flood zones 2 or 3) or larger than 1 hectare. Planning permission is usually not given until the FRA is approved by the Environment Agency.
Flood Risk Assessments must follow the National Planning Policy Framework, which replaced Planning Policy Statement PPS 25: Development and Flood Risk. PPS 25 was first introduced in 2001 and later changed. It aimed to improve how the planning system manages flood risk and helps communities adapt to climate change. PPS 25 required local authorities to consider flood risk during planning to avoid building in high-risk areas and to guide development to safer locations.
PPS 25 stated that flooding can harm lives and damage property, but its effects can be reduced through careful planning and management. To create an FRA, information about current and planned developments, flood levels modeled by the Environment Agency, and the site’s topography is needed. At the simplest level, an FRA can show whether a development is likely to be approved.
An initial idea of fluvial flood risk in an area can be found on the Environment Agency’s flood map website. FRAs analyze data to inform the Environment Agency about flood risk at a specific site and suggest ways for developers to reduce that risk. More detailed flood modeling can also be used to compare with the Environment Agency’s flood zone maps.
An FRA considers how flooding might affect the site and the local area, and how the development could influence flooding. It also includes recommendations to reduce flood risk for the development. FRAs must also examine flooding from all sources, such as rivers, groundwater, surface water, and sewer systems.
For sites in flood-prone areas, a sequential test may be required. This test helps ensure development is directed to locations with the lowest flood risk. The National Planning Policy Framework (NPPF) was updated in 2020 to require sequential tests for sites at risk of any type of flooding.
Northern Ireland
In 2006, the Planning Service, which is part of the Department of the Environment, released Planning Policy Statement 15 (PPS15): Planning and Flood Risk. The guidelines are careful and suggest avoiding building in flood plains and places that have had floods before. In special cases, a Flood Risk Assessment (FRA) can be done to support building in flood-prone areas. The Rivers Agency, which is the official group responsible for managing water and flood protection in Northern Ireland, provides advice on flood risk assessments to the Planning Service.
Republic of Ireland
In 2009, the Environment, Heritage, and Local Government Department and the Office of Public Works released planning guidelines. These guidelines require local authorities to use a step-by-step method for managing flood risks. Any new development in areas at risk of flooding must take a test to explain why the development is needed. This test includes a flood risk assessment.
United States of America
FEMA provides an online tool called the "Flood Map Service Center." This tool lets people enter their location or coordinates to check if their area is in a high-risk flood zone. The Service Center also explains how flood damage can affect homes and which homeowners are protected by insurance. "If you live in an area with low or moderate flood risk, you are five times more likely to experience a flood than a fire in your home over the next 30 years." Flood maps help people understand the risks in their area. It is important to follow advice from government officials and local news during a flood.
If evacuation is needed, have a plan ready. Check local news and alerts for information about how to prepare. If you do not have a car, arrange to move to higher ground in advance. "Flooding is the most common natural disaster in the United States."
NASA uses satellites to predict flood severity and help communities prepare, respond, and recover. This helps create plans for future weather events. Preparing for flood risks is important to protect homes and lives.
The Global Flood Monitoring System (GFMS) is a NASA satellite tool that uses real-time data to predict rainfall amounts. People can use the GFMS website to zoom into any location and see flood intensity for the current day and the past 3 and 7 days. This model was created by scientists from the University of Washington and the University of Maryland. The maps at the bottom of the website show information about "streamflow, surface water storage, and inundation" for each location.
These visuals help track changes across the country as Earth's climate warms. Water covers most of Earth and is essential for all people. It is necessary for life, but can become dangerous without proper preparation.
Worst Year of Flooding in the United States
2019 was recorded as the worst year for flooding in the United States. Factors such as heavy rainfall, fast snowmelt, record flooding, very wet soil, and delayed planting caused flood levels to reach record highs across the country. Heavy snowfall during winter in farmland areas, combined with snow melting before spring when crops are planted, damaged crops and made the soil too wet for farming. Sentinel-1 satellite images compare permanent water sources with floodwater. Farmers had to wait patiently for the soil to dry, which reduced the amount of food available for consumption and affected their ability to sell crops for profit. Without crops, farmers could not operate their businesses and had no choice but to wait for the soil to become usable again.