Environment Agency - Home

What do we mean by 'flood risk'

Flood risk is not just the likelihood of flooding, but the possible damage a flood could do as well. Find out more about how we measure it here.

When we talk about flood risk we mean two things

  • The likelihood of a particular flood happening, best expressed as a chance or probability over a period of one year. For example, 'There is a 1 in 100 chance of flooding in any given year in this location'.
  • The impact or consequences that will result if the flood occurs.

We need to know both how high the probability is of a flood occurring and the severity of any impact (which may change depending on how extreme the flood is). Only by determining both for a range of flood events of different size can we assess what the risk is to a particular area.

What is a flood risk assessment?

Flood risk assessments are our way of compiling information about the hazards and types of risk a flood presents, and their likely social, environmental and economic impacts. They help us establish the nature and scale of the existing risk, and how this may change over time or as a result of any flood risk management measures we put in place.

As well as historical data from past floods, we continually monitor present water levels. We develop models from this data to predict the course and severity of future floods. All this information goes into our Flood risk assessments, which particularly focus on:

  • Source of a flood, eg river, waterway, or tidal or coastal water.
  • Paths that the water will take during floods, and how the severity of a flood affects its path.
  • Impact on the people, land and property affected by flooding. This includes physical, emotional, social or economic harm.