Heat Force: A new operational 0–10 scale for environmental heat stress

As national meteorological services adopt thermal indices that account for more than air temperature alone, a key challenge is making these indices understandable and useful to professional users and the general public. In June 2026, the Royal Netherlands Meteorological Institute launched Heat Force, a new public-facing 0–10 scale for environmental heat stress based on the Wet-Bulb Globe Temperature (WBGT). It forms part of a broader conceptual framework that distinguishes environmental heat stress (Heat Force) from individual heat susceptibility (Heat Fitness). We examine its interdisciplinary co-design between 2024 and 2026, which drew on WBGT climatology (1991–2020), existing WBGT-based guidelines, testing alternative configurations, and expert input from meteorology, climatology, public health and thermal physiology. Several configurations were considered feasible, with the final design balancing multiple sources of evidence with operational and communication considerations. The final scale consists of uniform 2°C WBGT intervals, ranging from 0 (<14°C) to 10 (≥32°C). To assess initial operational interest, we conducted a survey with professional users (n = 46), of whom 78% expressed interest in using Heat Force. In addition, we analysed news-media coverage following the introduction of Heat Force in 2026, identifying 366 articles mentioning Heat Force, with substantial media attention both around its launch and during exceptional heat shortly thereafter. Heat Force provides a common framework for communicating WBGT to a broad audience, with potential to support decision-making across sectors. Separating the public-facing scale from the underlying index also allows future updates to the metric while retaining a familiar communication concept.