How do we communicate and warn about floods?

Flood warning systems turn forecasts into messages designed to reduce the negative impacts of floods. Warning systems should be accurate, timely and reliable. Prior community awareness of flood risk can make warnings more effective. Improving our warning systems could reduce social losses from floods.

Flood warning systems turn forecasts into messages designed to reduce losses

A warning system consists of a number of key steps: monitoring rainfall and river flow rate; making forecasts about river water levels and flood extent ; interpreting forecasts for their meaning in terms of impact on those at risk; composing and disseminating warning messages; response by those at risk and emergency services; and review and improvement (Figure 9).

In Australia, flood warning systems for rivers involve the Bureau of Meteorology (BoM), which provides forecasts of river water heights at specified locations to relevant authorities, and to the public via broadcast media and the BoM's website. Local government or State Emergency Services then interpret the BoM's forecasts to provide local information on areas likely to be affected, potential impacts and action advice to those at risk. Messages are also disseminated throughout the community, particularly by personal or informal networks. Social media (for example, Facebook, Twitter) will almost certainly play an increasingly important role in the future. This will also raise challenges due to the potential risk of mis-information.

Flash floods account for most flooding fatalities in Australia and currently present the most challenges due to the limited warning time. While the BoM provides severe weather warnings, which can include the risk of flash flooding, specific flash flood forecasts and warnings (i.e. including specific location and timing information) are not generally provided. However, some local governments have warning systems for these events.

Warning systems should satisfy a number of technical and communication attributes

They should be informative: Warning messages should indicate what the threat is, what action should be taken, by whom and when, in understandable, unambiguous and consistent language. A warning also needs to have personal meaning for those at risk (whether individuals, agencies or businesses). This means going well beyond a specified river height to indicating the area likely to be covered by the flood, its depth and speed in terms of locally relevant landmarks. In turn, this requires understanding of the relevant river systems.

They should be accurate: As warnings are predictions about the future, there is inevitably some uncertainty. Uncertainties can also arise from the construction and wording of warning messages themselves.Engaging with the community and business groups affected has been shown to improve understanding of the issues and reduce the chance that future warnings will be ignored.

They should be timely: Warnings need to allow enough time for appropriate action. This is particularly a challenge for flash floods.

They should be trustworthy: Warnings are more likely to be heeded if they come from multiple trusted sources.

They should reach the appropriate audiences: The audience for a warning will typically consist of many sub-groups, each with its own needs and expectations, preferred way of receiving warnings, and own ways of interpreting messages. No one warning source will reach, or be understood by, everyone. Warning systems work best when designed with the needs and expectations of the ultimate users in mind – something best achieved with their input. The capacity of individuals to receive or respond to warnings may be reduced because of disabilities, age, language, or other commitments.

They should be reliable: Warnings need to work under extreme conditions (for example, in inundated areas, in the absence of electricity), as this is when warnings are most needed. A variety of warning sources increases the likelihood that warnings will be maintained throughout a flood event.

Prior awareness of risk can make warnings more effective

For warnings to achieve their aims, people need to know about their community's flood risk, what actions will improve their safety, and how they will receive a warning to implement those actions. Prior awareness and preparation are key to success.

Those issuing warnings and advice need to know what sorts of actions are feasible for those who are being warned. This requires mutual learning between government agencies with formal responsibility for the warnings, and the people who need to respond to warnings. People need to see the personal relevance of the warnings to their situations – this is a major gap in many communities.

Community education programs can use a wide range of approaches, including community and industry facilitated climate, weather and flood workshops that identify community and industry risk and key management decisions. Another option is to run flood rehearsals or drills. A challenge is to maintain flood awareness and preparedness during the periods between floods.

Improving our warning systems could reduce losses

Improvements in warning systems, in particular in community response, is one of the most cost-effective means by which we could reduce the economic and social losses from floods and save lives.

Areas where current systems could be improved include:

  • Persuading people to take effective protective action once a warning has been issued. We know how to raise awareness, but not how to ensure action. This is a significant knowledge gap.
  • Using more locally relevant information so that people relate personally to warning messages, and know what to do for their own safety.
  • Reducing uncertainty in predictions while providing enough time for effective action, by harnessing the promise of advances in flood modelling and communication technologies. To date the advances in modelling and modern information and communication technologies have had limited impact on overall warning system effectiveness.
  • Communicating the uncertainties in warnings, possibly through a mix of verbal qualifiers like 'may', 'could', 'be at least' and probabilities. However, public appreciation of numerical probability statements is understandably limited.
  • Providing effective warnings for flash flooding. This is currently a major gap across Australia. Technical advances may now make flash flood warnings feasible, but the issues of rapid decision making by all the agencies involved and by those at risk would need to be addressed.
  • Improving methods to evaluate warning performance.

References and further reading