A new version of the Integrated Warning Service System in the Czech Republic

As of 1 January 2025, the Czech Republic has enacted a new Act on the Public Hydrometeorological Service, which, among other provisions, formally defines the Integrated Warning Service System (IWSS) and introduces the single‑voice principle for all warnings issued within this framework. The detailed structure of the warning system is specified in the implementing decree issued by the Ministry of the Environment of the Czech Republic. The new IWSS became fully operational on 1 July 2026.

The redesigned warning system, jointly operated by the Czech Hydrometeorological Institute (CHMI) and the Hydrometeorological Service of the Armed Forces of the Czech Republic, incorporates key elements of impact‑based warning approaches. Until now, the issuance of warnings relied on fixed mandatory criteria expressed as specific thresholds—such as precipitation totals over defined intervals, air‑temperature limits, probabilities of severe thunderstorms with a given hail diameter, or wind‑gust values. The decision‑making process was purely hazard‑oriented and based on a warning matrix evaluating the probability of occurrence and the forecast intensity of the hazardous phenomenon.

In the new warning system, threshold criteria serve only as indicative guidance, while the emphasis shifts from hazard to risk. The previous warning matrix has been replaced with a new one that jointly assesses the probability of occurrence (hazard level) and the expected impacts of the phenomenon (risk level).

Another major innovation in the CHMI warning system is the introduction of human thermal discomfort, represented by the newly established heat stress and cold stress warning groups. Further details on this embedded Heat Health Warning System are presented by the authors in a poster contribution in session OSA 2.4.

Acknowledgement: This work was supported by the Institutional Support for the Long-Term Conceptual Development of Research Organisation CHMI (DKRVO) 2023-2027 by the Ministry of the Environment of the Czech Republic.