Elements for Life

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HERE HAVE BEEN

many recent studies suggesting that

losses due to flooding have increased over the past

twenty years. Some studies claim that these losses have

been increasing at a faster rate than growth in population and

economic development. This in turn suggests that the number

of people in danger, the amount of property at risk and the

frequency of severe events may also be growing.

Flood forecasting and warning systems are an integral part

of emergency and floodplain management. Effective flood

warning systems maximize the opportunity for the imple-

mentation of response strategies aimed at securing the safety

of people and property, and reducing avoidable flood damage.

The total flood warning system concept has been promoted to

represent all of the elements of a system that need to work

together to provide effective forecasts and warnings. The total

system includes elements of monitoring, prediction, interpre-

tation, message construction, communication and protective

behaviour. For flood warning systems to be effective, they must

provide information for emergency service groups and the

public, that is timely, accurate, easy to understand and clear in

its practical application.

Specific requirements will depend on local conditions,

including the scale of the problem and the level of access to

information. However, as a general principle, initial require-

ments are:

• Advance warning of when a river will reach a specified

height that will cause flooding

• Sufficient warning lead-time for appropriate protective

action to be taken

• Awareness of the potential future level of flooding

• Assure awareness of the flood risk in the threatened

community.

Basic hydrological information, river height and flow, catch-

ment modelling capabilities and any additional weather

information that will contribute to the warning lead-time are

essential factors to the forecast and warning agency.

Concerns of information providers and user expectations

The primary issues and concerns for information providers

include the operation and maintenance of monitoring systems,

the quality of modelling capabilities, the accuracy (measure of

uncertainty) of the forecast and the amount of warning lead-

time that can be provided. In particular, key steps undertaken by

information providers include the operation of in-situ monitor-

ing and measuring devices (both rainfall and river level) and the

Disaster mitigation and preparedness:

flood forecasting and warning

Mr Bruce Stewart, President, WMO Technical Commission for Hydrology

Flood impact is usually widespread