Understanding and shedding
light on climate

Network dedicated to the study of the urban ‘heat island’ effect in Toulouse

Îlot de chaleur mesuré lors de la campagne expérimentale CAPITOUL du CNRM. © J. Hidalgo.
Heat island measured during the experimental CAPITOUL campaign by CNRM. © J. Hidalgo.


Temperatures are generally higher in cities than in rural areas, regardless of the season. During hot summer temperatures, such as summer 2017, this effect is particularly evident: significant temperature differences between cities and less urbanised surrounding areas are observed, particularly at night.

Detailed knowledge of urban climates and notably spatiotemporal characterisation of this phenomenon, referred to as ‘urban heat island’ (UHI) effect, across various districts is one of the major challenges involved in adapting cities to climate change. This subject has also been added to the institutional agenda with development of the new Plans climat air énergie territoriaux (PCAET - Territorial Climate-Air-Energy Action Plans) underway, in which the objective is to fight against climate change and adapt the territory to the latter.

Research conducted by Météo-France’s research centre on the subject for over 10 years, notably on air in the Toulouse area, resulted in the city’s urban community calling upon Météo-France to implement a UHI monitoring device. This network, owned by the urban community of Toulouse, will soon be made up of 60 measurement stations covering the entire city.

During the heatwave of June 2017, the first 9 stations already installed helped to characterise the UHI in the Toulouse conurbation in real-time. Prominent values were measured during the day in the city centre, with up to 39.8°C recorded on 22nd June, and a minimum temperature of 24.1°C overnight.

An UHI intensity indicator was defined, based simply on the temperature difference between the city centre (two measurement stations) and a town within the second ‘belt’ of the Toulouse conurbation. This indicator, which sits around an average of +1°C, often exceeded +2°C to +3°C at night during the episode (between 21:00 and 7:00 the next morning), with a record +4.5°C recorded on 22nd June at 22:15, the peak of the heatwave.

From a spatial perspective, there are significant differences between the various municipalities and districts of the city of Toulouse, in coherence with UHI mapping established during the CAPITOUL campaign in 2004.

Digital climate archives management tool

Visuel d'archives.

Météo-France holds approximately 10 linear kilometres of climate archives (meteorological observation records since the creation of the French meteorological service), which have been in the process of being logged across the agency’s various sites since 2015. Météo-France have also digitalised close to 2 million images of meteorological records.

These elements notably enable scientists to reconstruct past climates and provide data that feeds into climatic reanalysis carried out using climate change models.

In order to manage logs and images using a tool accessible by all, the ArClim project was launched in 2015 in response to a call for projects by the Secrétariat général à la modernisation de l’action publique (SGMAP - The Secretariat-General for Government Modernisation) entitled “Future audiences: innovating to modernise public action”. The project was selected, which helped fund the purchase and adaptation of archive management software, Seisan, developed by the company Naoned.

The software will be made available to all agents at Méteo-France for research purposes during the first quarter of 2018: it already contains over 60,000 logs and 660,000 images.


Extreme rainfall of increasing intensity in French Mediterranean regions

Le pont du Gard lors de la crue des 8 et 9 septembre 2002.
The Pont du Gard during the floods of 8th and 9th September 2002.


Episodes of heavy rainfall observed in Mediterranean regions feature amongst the most extreme weather events in mainland France. Many studies have sought to assess the evolution of these events in response to anthropogenic climate change using numerical modelling. The current study focused on the evolution observed for these events, using 55 years of available data.

A regional relative annual maximum daily rainfall intensity indicator was built by combining observations from 70 stations displaying good levels of temporal homogeneity. Changes in intensity based on this indicator were later assessed.

The results indicate significant intensification (for over 15 years) of extreme rainfall, estimated at +22% between 1961 and 2015, but with relatively significant uncertainty (intensification is between +7% and 39%). The wide range of values reflects the difficulty involved in precisely quantifying climate change in the series observed due to the natural variability of climate, which is particularly strong for heavy rainfall events. The observed intensification is consistent, albeit somewhat higher than intensification simulated by climate models. The study of other indicators such as the number of events, size of impacted areas, or volume of rainfall beyond a given threshold, result in the same conclusions concerning the recent evolution of these events.

These studies support the view that extreme events will become more intense in warmer climates; an especially useful diagnosis in terms of adaptation. They could be extended to other regions, or used for monitoring climates in Mediterranean events.

Website dedicated to storms in mainland France

Carte extraite du site tempête : vent instantané maximal lors de la tempête Zeus qui a balayé la France les 6 et 7 mars 2017, avec de violentes rafales atteignant jusqu’à 190 km/h à Ouessant dans le Finistère. © Météo-France.
Map extracted from storm site: maximum instantaneous wind during the Zeus storm that swept across France on 6th and 7th March 2017, with severe gusts reaching up to 190 km/h at Ouessant, in Finistère. © Météo-France.

In 2017, Météo-France launched a website dedicated exclusively to storms in mainland France: http://tempetes.meteofrance.fr/.

The website groups scientific explanations and various unpublished climatological databases in order to understand the meteorological phenomenon. As such, over 300 storms have been identified and analysed since 1980. Ninety historical events since 1703 are detailed on fact sheets, whilst statistics on strong winds from 70 professional weather stations have also been made available.

Articles on storm origins as well as the tools and methods used to analyse them and identify their climatological characteristics in relation to climate change can also be accessed.

The website incorporates data from recent storms to date, including Zeus, which occurred on 6th and 7th March 2017 and ranked amongst the 15 most severe events since 1980.

Discover the other chapters of the current part