Operational cycle of multi-hazard early warning systems
Multi-hazard early warning systems structure their operation around four distinct operational phases: detection, prediction, warning issuance, and response coordination. In the detection phase, the integration of heterogeneous sources — in situ sensors, Earth observation imagery, pluviometric data, and hydrological models — enables characterisation of the initial state of the hazard. For phenomena such as flash floods or coastal storms, the latency between data acquisition and processing directly conditions the operational utility of the system. The continuous coverage provided by satellite segments is particularly relevant in areas with limited ground-based observation infrastructure. The prediction phase introduces the greatest technical complexity in the cycle. Numerical meteorological and hydrological prediction models operate with temporal horizons and uncertainty levels that vary according to the hazard under consideration. In the case of droughts, the prediction horizon may extend to weeks or months, whereas for flash-flood catchments the working window is a matter of a few hours. The fusion of observation data with outputs from prediction models requires robust assimilation frameworks and well-calibrated threshold criteria for each event type and geographical area. The management of false positives constitutes one of the principal operational challenges of these systems. An excessively conservative alert threshold generates frequent warnings that reduce the credibility of the system in the eyes of authorities and the public, a phenomenon known as alert fatigue. An excessively high threshold, by contrast, increases the risk of missing real events. The calibration of these parameters requires ongoing statistical analysis of the system's historical performance and cross-validation against records of documented events, a process that must be reviewed periodically in view of the variability of climatic conditions. The issuance of the warning and its communication to the public and to operators of critical infrastructure require differentiated protocols according to the recipient. Administrations and infrastructure managers require structured technical information — severity level, affected area, estimated temporal horizon — that enables the activation of specific contingency plans. Public communication, by contrast, must prioritise the clarity and actionability of the message, avoiding ambiguities that hinder individual response. Coordination between both channels, under regulatory frameworks such as those established by the European Flood Risk Management Directive, largely determines the actual effectiveness of the system at the critical moment.
NASSAT - Network Satellite Systems