In HEC-FIA the warning issuance defines the moment a warning is issued to the population at risk. The issuance of warning can be generated as the result of a hydraulic event (e.g. the exceedance of a specified stage at a particular location or appearance of water on the interior side of a levee) or the passage of an amount of time in the model simulation (e.g. thirty minutes after the start of the simulation). A lag can be specified to simulate the time between the physical occurrence of the event and the human response of issuing a warning in response to that event. If the user defines a warning issuance relative to a rule that uses a specific location and threshold, the warning issuance is dependent upon a particular inundation configuration and hydraulic event. If the user defines a warning issuance relative to start time, the warning issuance works with any alternative, and is dependent upon the start time of the time window used in the simulation.
Warning issuance times are a critical component of the life loss computation, and can be a major source of uncertainty in the life loss results. For instance, if a house is located close to the river near a dam, inundation can occur quickly and the warning issuance may drive loss of life estimations. On the other hand, when inundation occurs hours after the occurrence of a particular event, warning issuance may not be the most important factor in the computation of loss of life risks.
Warning issuance times also impact economic losses through the evacuation of cars during loss of life computation. Each occupancy type has a car carrying capacity, and each structure has a number of cars and people associated with it. The number of people that evacuate safely determines how many cars are left in the floodplain to be damaged.