The Heat Health Warning Systemi in the Czech Republic

In 2026, the Czech Republic completed a comprehensive reform of its national Impact‑Based Warning System (IWSS), driven by new legislation including the Act on the Public Hydrometeorological Service and its implementing decree issued by the Ministry of the Environment. A key innovation is the introduction of two new warning categories—Heat Stress and Cold Stress—which together form an embedded early warning subsystem targeting expected human thermal discomfort. This marks the first official establishment of a national Heat Health Warning System in the Czech Republic.

The core of this system is the assessment of anticipated thermal stress using the Universal Thermal Climate Index (UTCI), specifically its forecasted daily extreme values as well as daily means. The system therefore evaluates not only the peak stress represented by the relevant extreme (UTCI_max for heat stress and UTCI_min for cold stress), but also the duration of stressful conditions without sufficiently long recovery intervals for the human organism. Combining both perspectives enables the detection of expected heat waves and cold spells characterized by several consecutive days of elevated physiological burden.

The Czech Hydrometeorological Institute (CHMI) adopted this approach following the recent availability of UTCI outputs from numerical weather prediction models and the development of a UTCI climatology for the Czech Republic for 1991–2020 within the PERUN project, which provided an objective basis for defining warning criteria.

These warning products are intended primarily for the Integrated Rescue System of the Czech Republic, but also for national authorities (notably the Ministries of Health and Labour and Social Affairs) and regional and municipal administrations. With the operational launch of the system on 1 July 2026, the state now has a clearly defined, unified foundation for the long‑delayed development of a national Heat Health Action Plan, as well as for subsequent regional and municipal action plans, particularly in larger urban areas.

Acknowledgement: This research was founded by Technology Agency of the Czech Republic, grant number SS02030040, project name „Prediction, Evaluation and Research for Understanding National sensitivity and impacts of drought and climate change for Czechia“.