A flood warning turns a prediction or forecast into information on which many actions are dependent. The fundamental purpose of the warning is to enable individuals and communities to respond appropriately to a major flood threat to reduce the risk of death, injury and property loss. The ultimate end-user of a flood warning is the public, which faces impacts on its housing, possessions, land, livestock and transport. The basic requirement is for people to have time to take necessary actions and make arrangements, which can range from putting protection or proofing arrangements in place, to evacuation, along with basic possessions and livestock, to a place of safety. Flood warnings, therefore, are required to inform those at risk on the timing and extent of the flood, so that they know how long they have in which to act, which areas will be affected by the flood, and, most importantly, which escape routes or accesses to shelter are available (WMO N° 1072).
The type of flood warning service available varies greatly from country to country. An also do their names, their positions in government structures, their legal framework, etc.
To keep their observational and modelling capabilities fit for purpose and adequate for responding to evolving user demands, NMHSs could ask for the cooperation of academic institutions and private companies.
Examples of different types of national flood forecasting and warning systems are presented in the following sections.