Forest fires and heat wave: a particularly intense summer observed by AERIS

An extreme heat wave is currently affecting Portugal, Spain and France. Major fires have also broken out in these three countries, notably in the south-west of France where more than 2,700 hectares of forest went up in smoke on 12 July. Since Saturday, Greece has been hit by a heat wave expected to last ten days, with temperatures of 42 degrees expected in some areas, raising fears of more fires.
New absolute heat records were also recorded on Tuesday along the north-western coast, such as in Dieppe (Seine-Maritime), where the station, opened in 1949, recorded 40.4°C, compared with a previous record of 40.1°C on 25 July 2019. Another absolute record in the Pas-de-Calais, with 39.6 °C in Boulogne-sur-Mer (37.9 °C on 31 July 2020). According to Météo-France, this is the 45th heatwave in mainland France since 1947 and their pace is accelerating. Over the last 35 years, there have been three times as many heat waves as in the previous 35 years.

Temperature anomalies observed with the Atmospheric Infrared Sounding Interferometer (IASI) instrument from the EUMETSAT METOP satellites. This instrument was designed for operational meteorology and atmospheric chemistry and climate monitoring. The animation and images below show the temperature anomalies measured in June compared to the June temperatures of the last 14 years.

The violent forest fires in south-western France can be seen in the Sentinel3, VIRRS and geostationary satellite images collected by our ICARE data centre. The progression of forest fires in the Landes region can be clearly seen on these two images taken between 14 and 18 July.

The heat wave in France has also been observed thanks to the various measurement campaigns in the Ile de France region which took place within the framework of PANAME where AERIS is involved. After 50 hours of flight of a research aircraft in the Paris region, 48 launched meteorological balloons and 28 mini-balloons, 15 state-of-the-art atmospheric remote sensing instruments spread over 5 urban and peri-urban sites, the PANAME research initiative, which studies air quality and urban climate in the Paris region, delivers its first results.

The ACROSS measurement campaign was able to provide airborne measurements (nearly two tons of instruments were installed on board the SAFIRE aircraft to directly measure the chemical composition in the atmosphere, both the gases (ozones, nitrogen oxides, volatile organic compounds, etc.) and the particles found there) and thus sample the same pollution plume several times at different distances from Paris in order to identify the sources and transformations of these chemical compounds. An exceptional episode of high heat occurred in mid-June. During this period, higher concentrations of secondary pollutants and more intense forestry emissions were observed. The end of the campaign was marked by the return of intense heat conditions and the transport of the Parisian plume towards the project’s measurement sites.

Measurements from weather balloons and ground-based instruments (48 conventional weather balloon releases took place in Paris and 28 mini-balloons in several areas of the Paris region) documented strong contrasts in the temperature profile above the surface, and in particular measured the “thickness” of the urban heat island at night during the heat peak in mid-June. Thus, it was observed that the cooling effect of the Vincennes park extends over a height of about 150 m, and is more intense at sunset (of the order of 5 to 7°C on certain nights compared to the quays of Bercy) than later in the night, of the order of 3°C.

Finally, during the hot spells of 16 to 18 June, automatic lidar profiles and balloon probes revealed a gradual descent of very hot air loaded with aerosols from North Africa. The temperature profiles show this very warm air (> 36 degrees – in red in the figure) moving over the region between 2000 and 4000 m, then entering abruptly into the urban atmospheric mixing layer (outlined by the white triangles) on 18 June, causing temperatures to rise by a further 5 degrees. Desert dust aerosols carried aloft also entered the urban mixed layer and produced a surface pollution peak on the night of 18 June.

Other results are expected and will be available on the Paname portal developed by AERIS to facilitate the cross-use of this data set and its dissemination to the scientific community.

It is important to remember that the multiplication of these phenomena is a direct consequence of climate change, with greenhouse gas emissions increasing both their intensity, duration and frequency.