Heatwave Analysis: Methods for Recording Temperature Data
In the sweltering summer heat of 2025, France has once again been gripped by a relentless heatwave. The second wave of this year's extreme temperatures has resulted in several temperature records being broken, with the majority of these records being shattered since the historic heatwave of 2003.
Météo-France, the French national weather service, plays a crucial role in recording and verifying these temperature extremes. Their meteorological stations, located across the country, are equipped with standardized instruments designed to minimize external influences and ensure accurate temperature readings.
Temperature is recorded using meteorological sensors, often electronic temperature probes, housed in standardized shelters known as Stevenson screens. These stations operate continuously, recording temperature at regular intervals, including minimum and maximum daily temperatures and sometimes more frequent values.
The raw temperature data collected are subject to several automated and manual quality control steps. These include checks for sensor malfunctions, implausible sudden jumps or drops in temperature, comparison with nearby stations, and correction for known biases or errors.
To verify a temperature record, Météo-France compares the recorded values against historical data, verifies instrument calibration status, and cross-checks with nearby reference stations. This may involve reanalysis of sensor data and meteorological context confirmation, such as weather patterns. The verification ensures the record is not an artifact of instrumentation or recording error.
When a record is broken, the reliability of the measurement is controlled by comparing the collected data with that of the closest stations. Météo-France adheres to international standards for meteorological observations, including equipment calibration, siting standards (to avoid artificial warming), and data archiving protocols that permit long-term climate monitoring and reliable extreme value detection.
The temperature must be measured 1.50m above the ground and inside a shelter for a record to be registered. The shelter used for temperature measurement is painted white and ventilated, representing the shade temperature. Météo-France weather stations are installed above a vegetation cover for representative temperature measurement.
In cities, Météo-France stations are often located in parks, ensuring the sun's path is not hindered by hedges, tall trees, or tall buildings. The city of Bordeaux recorded a temperature of 41.6°C on Monday, August 11, while the city of Angoulême reached a staggering 42.3°C on the same day. The record temperature in Paris, 42.6°C, was recorded on July 25, 2019.
Six absolute temperature records were broken on Monday, August 11, and at least five on the following day. Almost all the temperature records in France date from the 21st century, according to climatologist Simon Mittelberger. The August 2025 heatwave is the 51st recorded since 1947, and half of them have occurred after 2011, signifying the acceleration of climate change linked to our greenhouse gas emissions.
Météo-France checks for any external events that could have skewed the measurement, such as a cut-down tree or a nearby fire. The temperature in Paris has been recorded at the Parc Montsouris since 1867, providing a long-term record of the city's climate.
Over 2,500 official meteorological stations measure temperature with real-time data transmission, ensuring that France remains well-informed about its changing climate.
