Heat stress along the 2026 Tour de France: a spatiotemporal reconstruction of exposure across race stages

Anthropogenic climate change is amplifying the intensity and frequency of extreme summer heat across Europe, posing critical thermal challenges for major outdoor endurance events. However, existing sports heat protocols typically rely on static weather measurements, failing to capture the microclimatic variability encountered by a moving event. Here, we present a high-resolution spatiotemporal reconstruction of environmental heat stress across all 21 stages (~ 3,323 km) of the 2026 Tour de France. By integrating ERA5 reanalysis and WRF mesoscale modeling (~ 1 km resolution) corrected with ground station networks, modeled the Universal Thermal Climate Index (UTCI) and the Wet-Bulb Globe Temperature (WBGT) paired with estimated peloton passage times. Strong to very strong heat stress (UTCI ≥ 32°C) accounted for 60.5% (2,009 km) of the total route distance and 57.8% (2,991 min) of estimated riding time, peaking at 44.5°C in Stage 4. Although no segment exceeded the Union Cycliste Internationale (UCI) threshold for stage suspension (WBGT ≥ 32.2°C), 175.9 km fell within high-risk Red band conditions (WBGT ≥ 28°C). This index divergence reveals that while dynamic athlete movement can mitigate immediate regulatory breaches, static roadside spectators endure prolonged exposure under dangerous radiant loads. These findings underscore the need for mobile, spatiotemporally resolved biometeorological frameworks in sports safety protocols and event scheduling.