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