Heat guidance

For riders

WBGT (Wet Bulb Globe Temperature) combines air temperature, humidity, wind, and solar radiation into a single heat-stress number — it's a better measure of real physiological load than air temperature alone, because it captures how much the body can actually cool itself by sweating in the given conditions.

Elite exertion changes the risk calculus: sustained high-power output generates substantial internal heat regardless of ambient conditions, and elite cyclists have recorded core temperatures of 39–41.5°C during hot races. Airflow at speed and downhill recovery sections provide some cooling that a stationary WBGT reading doesn't capture — which is part of why the UCI's 28°C threshold sits above general occupational safety limits (ISO 7243 uses 25°C for high-exertion work).

The UCI High Temperature Protocol maps WBGT to five risk tiers, each with escalating measures:

WBGT	Tier	Action
< 15°C	Very low-risk	No specific measures.
15–17.9°C	Low-risk	Warm-up in the shade with fans.
18–22.9°C	Moderate low-risk	Ice vests, wet towels, individualized hydration plans, ice socks.
23–27.9°C	Moderate high-risk	Shaded start areas, more drink/ice motorbikes, adapted hydration rules.
≥ 28°C	High-risk	Modified start/finish times or route, or cancellation.

Basic prevention — pre-cooling, staying ahead of fluid losses rather than drinking to thirst, and heat acclimatisation over 1-2 weeks before a hot event — is drawn from established sports-medicine guidance and the UCI protocol itself, not a substitute for advice from a team doctor or physiologist.

For roadside fans

Spain's AEMET (Agencia Estatal de Meteorología) uses a three-level colour code for heat — relevant for stages 5–21 of this edition, almost the entire route. Monaco and France (stages 1–3) fall under Météo-France's own vigilance system instead, and Andorra (stage 4) under its national service — neither is covered in detail here.

Aviso amarillo (yellow)— low risk to the general population, but a real risk for specific activities. AEMET's recommendation is simply to stay aware; thresholds vary by region's own climatology (roughly 34–36°C inland, lower on the coast and in the mountains).
Aviso naranja (orange) — a real danger for everyday activities. Unusual-intensity heat; avoid unnecessary travel in the affected area during peak hours.
Aviso rojo (red) — very high risk to the population, exceptional intensity, a direct threat to public safety. Travel is discouraged; prioritise shade and cool spaces.

No colour shown means AEMET has not issued an active warning for that area — it is not itself a fourth "safe" alert level, unlike France's four-level system.

What the protocol means

The UCI's Extreme Weather Protocol (2015, covering cold, wind, snow, and visibility as well as heat) was extended with a dedicated High Temperature Protocol in 2023–24, using the WBGT tiers above. At the red tier, the UCI can modify a stage's start or finish time, shorten or reroute it, or cancel it outright.

This edition saw both mechanisms used for real: stage 15 (Palma del Río → Córdoba) had its neutral start delayed and its route cut short under the Extreme Weather Protocol for forecast extreme heat, and stage 3 (Gruissan-Aude → Font Romeu) was cancelled mid-race — though for hail, not heat, a reminder that the UCI's wider Extreme Weather Protocol covers more than just high temperatures.