How do heatwave alert levels work in Lyon?
If the Rhône department, like a large part of France, is on orange heatwave alert this Tuesday, July 1st, how do the different alert levels implemented by Météo France work?
Météo France uses a heatwave warning system to inform about the dangers associated with heat waves. This system is based on colored warning levels (green, yellow, orange, and red).
- Green Vigilance :
- No particular danger. Temperatures remain within seasonal norms.
- Yellow Alert :
- Corresponds to a heat peak, either a short period (1 to 2 days) of intense heat, or a persistent heat episode (more than 3 days). This level indicates a risk for vulnerable populations and those exposed to difficult working conditions.
- Orange Alert :
- Indicates a heatwave, i.e., a period of intense heat lasting at least 3 consecutive days and nights. This alert level indicates a health risk for the entire exposed population.
- Red Alert :
- Refers to an extreme heatwave, exceptional in its duration, intensity, or geographic extent. It has a significant health impact on the population and can have significant societal consequences (drought, water supply, business interruption).
Alertness levels are determined based on several criteria:
- Maximum and Minimum Temperatures : Temperature thresholds vary by department to reflect local climate differences. In Lyon, for example, the heatwave threshold is triggered when at least three consecutive days are forecast with nighttime temperatures above 20°C and daytime temperatures above 34°C.
- Duration of the Episode : An episode is considered a heatwave if it lasts at least 3 days.
- Health Impacts : The thresholds take into account epidemiological studies on the health impacts of extreme heat (headaches, nausea, cramps, dehydration, heat stroke). Hospital saturation may also be a factor in a department's move to red alert.
- Aggravating or Mitigating Factors : Elements such as the duration of the episode, precocity, pollution, and humidity are also taken into account.
Météo France evaluates weather forecasts by comparing them with benchmarks established by Public Health France. It is by comparing them to past events that it estimates the appropriate level of vigilance ( Meteo France ).
Lyon Capitale
