Description: This dataset accompanies the study "Locked in heat: present-day thermal constraints on Summer Olympic host cities and the limits of operational adaptation" (Defrance & Gadais). It provides Wet-Bulb Globe Temperature (WBGT) indicators characterising summer heat-stress constraints on Summer Olympic competition, derived from the ERA5-Land hourly reanalysis. Source data. All indicators are computed from the ERA5-Land hourly reanalysis (Muñoz-Sabater et al., 2021), 0.1° × 0.1° (~9 km) spatial resolution, distributed by the Copernicus Climate Change Service (C3S). Source variables: 2 m air temperature (t2m), 2 m dewpoint temperature (d2m), 10 m zonal and meridional wind components (u10, v10), and surface solar radiation downwards (ssrd, de-accumulated to instantaneous hourly mean flux). Temporal coverage: July and August only, 2006–2025 (20 years), the months encompassing the modern Summer Olympic Games. WBGT computation. WBGT is reconstructed using the Stull (2011) psychrometric approximation for the natural wet-bulb temperature and the Hajizadeh et al. (2017) empirical regression for the black-globe temperature. Two formulations are provided: outdoor (sun-exposed), WBGT = 0.7 Tw + 0.2 Tg + 0.1 Ta (Yaglou & Minard 1957 weighting), with full solar load; and indoor/shaded, following the ISO 7243 shade formulation with incoming shortwave radiation set to zero. Contents. Global gridded indicators (global_days_gt28_2006-2025.nc, NetCDF): mean number of July–August days per season with at least one hour exceeding WBGT thresholds, on the full ERA5-Land land grid. Variables: days_gt28_outdoor, days_gt28_indoor, days_gt32_outdoor, days_gt32_indoor. Thresholds: 28 °C (high heat-stress risk) and 32 °C (extreme risk), per international sport-federation guidelines. City-scale hourly series (hourly_<City>.parquet, 8 cities): hourly time series in mean local solar time, July–August 2006–2025, with WBGT (outdoor and indoor) and its components (Ta, RH, Tw, Tg_sun, ssrd). City-scale derived indicators (CSV): city_summary.csv (per-city constrained-day counts at both thresholds and formulations, peak-hour WBGT decomposition, 2006–2025 linear trends); diurnal_<City>.csv (percentage of hours exceeding each threshold by local hour); yearly_<City>.csv (annual constrained-day counts). Analysis code is archived together with the data and at [GitHub URL]. Study cities (nearest valid ERA5-Land land cell): Doha (QA), Ahmedabad (IN), Tokyo (JP), Los Angeles (US), Paris (FR), Rio de Janeiro (BR), Brisbane (AU), Cape Town (ZA). Scope. Present, observed climate only; no future projections. WBGT is a first-order indicator at the regional near-surface scale and does not resolve intra-urban or venue microclimates.