Flood-threat recognition systems may include flood forecasting using technology appropriate to
the situation as well as the capabilities for assessment and operational support. The value of the forecast
is derived from the additional lead time made available for the response effort to reduce impacts.
There are trade-offs between the accuracy and the timeliness of advanced warnings; typically, rapid
assessments are less accurate, but extended analyses can lengthen the time for threat recognition
and response. Warning dissemination is an additional key element in order to get messages to public
safety authorities in a timely manner and in understandable formats. Advanced warnings can be
used to motivate evacuations and guide deployment of assistance. With longer lead times, more
aggressive actions may be accomplished, such as drawing down reservoir levels to increase capture
capacities, moving vehicles and materials from low-lying areas, or initiating flood-fighting efforts.
Mathematically, warning time can be described as (USACE 1996)