Decision-making with probabilistic flood forecasts

This report describes a practical framework for using probabilistic flood forecasts to support decision-making in flood incident management.

Decision-making with probabilistic flood forecasts
Decision-making with probabilistic flood forecasts

Who wrote this?

Main Authors Murray Dale and Jon Wicks of Halcrow Group Ltd, with collaboration from Kings College London, Met Office, and Florian Pappenberger.


It was first published in April 2013.


This guide illustrates a number of simple methods which could be used to support clear, consistent, and objective decisions. The methods have been developed and tested on a range of flood locations and types in Environment Agency R&D project Applying probabilistic flood forecasting in flood incident management (SC090032). This aims to remove the subjectivity of the decisions made from probabilistic flood forecasts.

Who should read this?

For any engineers concerned with operational flood management and anyone involved in making decisions before a flood event when probabilistic flood forecasts are available. Flood Forecasting Centre operational hydrometeorologists and Environment Agency Regional Flood Forecasting duty staff.


This paper includes three decision-support methods:

  • Basic method – use a probability threshold for a specific FIM action based on judgement and local knowledge (e.g. 20, 40, 60 per cent)
  • Simplified method – use a probability threshold based on the ratio of FIM action cost and the monetised benefit of that action (a cost-benefit approach in the widest sense)
  • Detailed method – establish a water level-impact relationship for use in real time and, in real time, determine whether average flood impact of the forecast water levels (if no FIM action is taken) is greater than the FIM action cost

For more information and questions

Please contact Charles Jensen (

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