A summer of heatwaves and drought for many

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Summer 2018 in much of Europe was characterised by prolonged heatwaves, leading to droughts in some areas.

A summer of heatwaves and drought for many
Date & Time
May–September 2018
Satellites
Meteosat-9,10,11, Metop, Aqua
Instruments
SEVIRI, ASCAT, MODIS
Channels/Products
Natural Colour RGB, ASCAT Soil Moisture, Brightness Temperature, Sunshine Duration Anomaly, Daily Temperature Anomalies, LSA SAF FVC, True Color

By Mark Higgins, Jochen Kerkmann, Vesa Nietosvaara, Jose Prieto and Christine Träger-Chatterjee (EUMETSAT), Ivan Smiljanic (SCISYS) and Sancha Lancaster (Pactum)

Summer 2018, and in some cases late spring, saw exceptional hot and dry conditions in large parts of Europe — leading to droughts, heatwaves and wildfires.

Figure 2
 
Figure 2: Sunshine Duration Anomaly 2018 [%] (January to August) relative to the 35-year (1983-2017) climatology Source: CM SAF

Most of the areas affected by drought were across northern and central Europe, including Austria, Denmark, Finland, France, Germany, Ireland, Lithuania, Sweden, the northeastern part of Switzerland, and the UK. Because of the drought, farmers experienced a significantly reduced harvest, leading to concerns about food shortages in the coming months.

Wildfires were reported in Denmark, Finland, Germany, Greece, Latvia, Norway, Portugal, Sweden and the UK, severely damaging 100s of acres of scrubland, forests and moorland.

Maximum and mean temperature records were broken in many places, for instance in Lapland where 33.4 °C was recorded at Kevo on 18 July, an all-time record for that region.

Figure 2 provides the broad view of the sunshine duration anomaly for Europe, following analysis by Uwe Pfeifroth of the CM SAF. It shows that large parts of Central and northern Europe received significantly more sunshine hours than usual. This positive anomaly was around 25%, with more than 50% in parts of the UK and Scandinavia. However, southern Europe was slightly less sunny in 2018.

For the majority of Europe, long lasting heat and drought conditions ended with the passage of a cold front on 27 August 2018 (see case study on August snowfall in the Alps), only to regain vigour over the Alps and northern Italy, lasting until 30 September.

By using image statistics (averages, maxima and minima) we can compare the three-month period of May/June/July in 2018 with the same period in 2017.

On the averaged Meteosat solar channels scans at 14:00 UTC every day in the 92 day period (Figure 3), the presence of cloud can be seen as haziness. More haze means more cloud coverage over that period, therefore less sun which means less daily heating. Scandinavia and north western Europe, for instance, were significantly more sun-bathed than a year ago, however, Italy and Greece were less.

Solar image comparison
Image from May/June/July 2017 Image from May/June/July 2018
Figure 3: Comparison of Meteosat solar channels at 14:00 UTC every day in May/June/July in 2017 and 2018.
 

High temperatures

 
 
Figure 4: FMI anomalies of daily temperatures 1 June–22 August 2018.

The summer was exceptionally warm in many places, even up to the northernmost regions in continental Europe. Figure 4 shows the daily maximum temperature anomalies in Finland; some of the most pronounced anomalies, up to 2.7 °C higher than average, can be seen in the northernmost part of the country.

Maximum temperatures

  • The Met Office reported the summer had been the warmest on record in England, with a provisional average figure of 17.1 °C.
  • In Ireland Met Eireann reported that 32 °C was recorded at Shannon Airport, County Clare on 28 June, the highest temperature ever recorded in the country.
  • The Austrian met service ZAMG reported that the summer had been the fourth warmest on record, with two to three times as many heat days (at least 30 °C) as in an average year.
  • In France Meteo France reported the country had the second warmest summer on record, with above 30 °C daily maximum for 26 days in Paris-Montsouris.
  • The highest summer temperature in Finland was 33.7 °C, record in Vaasa.
  • Svanhovd environmental centre in the Pasvik valley, Norway, measured 33.3 °C on 18 July, beating the previous record of 33 °C at Banak airport on 22 July 1988.
  • Uppsala, southern Sweden, hit 34.4 °C, its highest temperature since 1975.

Figure 5 shows the maximum infrared 10.8µm brightness temperatures during the day at the end July 2017 and 2018. It emphasises the sea temperature of around 15 °C, as compared with the previous summer (values are from 10 °C (blue) to 20 °C (red)). The surface water temperatures are a good reflection of how warm the atmosphere has been. The Baltic Sea shows a positive anomaly of about five degrees above the previous year. North of Spain, however, the sea waters were colder this year.

Note: 10.8µm brightness temperatures (BT10.8) are several degrees below actual sea surface temperature, due to water vapour absorption, especially near limb areas of the Meteosat field of view, like Scandinavia.

Infrared image comparison
Image from July 2017 Image from July 2018
Figure 5: Comparison of maximum infrared 10.8µm brightness temperatures from July 2017 and 2018.

Drought

The animation (Figure 6) shows the soil moisture across Europe from the beginning of May to the beginning of September. The blue areas have more soil moisture and the red areas less.

The source data is from ASCAT on board EUMETSAT's Metop satellites, which is then assimilated into a model that estimates the moisture at different levels for different plant root depths — the animation shows the soil moisture from 7–28 cm depth. The data is from EUMETSAT's Hydrology SAF


Figure 6: Metop ASCAT Soil Moisture Product, 1 May to 5 Sept 2018. Download animation (MP4, 1 MB)
 
 
Figure 7: The soil to 1.80 m depth was the driest (dark red), especially in the northwest, in the middle and in the extreme south. Orange colours depict a moderate drought. Credit: UFZ

Germany received only about half its normal yearly rainfall. In many parts of the country the water level in rivers reached their lowest levels for a century. The water level on the Oder River in Frankfurt dropped to 93 cm (three feet), the lowest level since records began.

Figure 7 shows the situation in Germany, as reported on 17 August by the Helmholtz Center for Environmental Research (UFZ).

At that time half of Germany was affected by extreme drought and almost 90% had dry soil, especially from Schleswig-Holstein to North Rhine-Westphalia, in Saxony, in southern Baden-Württemberg and in eastern Bavaria.

Impacts of drought on vegetation

These dry and hot conditions had a devastating, cumulative effect on vegetation. This is apparent when looking at the shades of green ‘vegetation colour’ from Natural Colour RGB product. The lack of the rain and the constant sun and heat stress had an impact on the photosynthetic processes in the plants, with reduced chlorophyll concentrations — the substance responsible for absorption in the 'green' component of this RGB.

Using Meteosat Natural Colour RGB imagery to do an analysis of Europe on the same day for the past 10 years, clearly illustrates the change in the state of the vegetation.

Figures 8 and 9 are animations of the Meteosat Natural Colour RGBs, over the whole of Europe, and zoomed in on Central Europe, for 22 August at 12:00 UTC, from 2008 to 2018.


Figure 8: Meteosat Natural Colour RGB animation over Europe, 22 Aug 2008 12:00 UTC–22 Aug 2018 12:00 UTC, time step one year. Download animation (MP4, 2 MB).

Looking at Figure 8 one can conclude that many regions were under drought conditions (brown coloured areas). The most affected area was the northern belt of Europe, stretching from the northern half of France all the way to the Black Sea. Regions along the Mediterranean Sea suffered less droughts this summer, as relatively frequent convection episodes brought precipitation and cooled off the atmospheric boundary layer.

Zooming in on the central parts of the Europe (Figure 9), it becomes apparent that 2018 had the worst vegetation conditions at the end of August.


Figure 9: Meteosat Natural Colour RGB animation, zoomed in over Central Europe, 22 Aug 2008 12:00 UTC–22 Aug 2018 12:00 UTC. Download animation (MP4, 2 MB).

Plenty of brown shades reveal dry or no vegetation in areas. The green areas correspond with mostly forest areas, where vegetation managed to withstand the stress from the sun, heat and lack of rain.

Crops, grass, bushes and other types of vegetation could not withstand such long-lasting conditions. Higher terrains like southern Germany, Austria and Slovakia, which mostly correspond to forest areas, had a bit more rainfall and less evapotranspiration, i.e. better conditions for the health of the vegetation.

The Land Surface Analysis (LSA) SAF Fraction of Vegetation Cover (FVC) products from 16 June and 16 August 2018 (Figure 10), show the period when, generally, the drought was more pronounced. The black tones are fractions close to zero (less vegetation), and the white tone as close to 100% (more vegetation). The image from 16 August shows a fast drop in the levels of vegetation cover compared with 16 June.

Land SAF image comparison
Image from June 2018 Image from August 2018
Figure 10: Comparison of Land SAF Surface Analysis Fraction of Vegetation Cover (FVC) products from 16 June and 16 August 2018.

The status of vegetation health can also be assessed by comparing the Meteosat-11 Natural Colour RGB with the Fraction of Vegetation Cover product (Figure 11), which shows good overlapping of soil and vegetated surfaces. The MSG Daily Fraction of Vegetation Cover (MDFVC) product discriminates between soil and vegetation surfaces, presented in Figure 11 using intuitive colours (shades of green and brown).

Land SAF image comparison
LSA SAF FVC product, 22 Aug, 00:00 UTC Natural Colour RGB, 22 Aug, 12:00 UTC
Figure 11: Comparison of Natural Colour RGB and the Land SAF Surface Analysis Fraction of Vegetation Cover (FVC) product 22 August.

Vegetation degradation continued in the month of September. Comparing Meteosat-11 enhanced Natural Colour RGB data for similar dates in August and September (Figure 12) it becomes obvious that this was true for most of Europe, with extreme vegetation loss in areas that until September had relatively good vegetation health — south and south-east Europe. Loss of vegetation in September is, as expected, enhanced by the natural yearly vegetation lifecycle.

Natural Colour RGB image comparison
Image from 22 August 2018 Image from 20 September 2018
Figure 12: Comparison of enhanced Meteosat-11 Natural Colour RGBs from 21 August and 20 September 2018.

Wildfires

Portugal

Figure 13
 
Figure 13: Aqua MODIS True Color RGB, 7 August 2018, 13:45 UTC

The Aqua MODIS True Color RGB image shows, enclosed in red rectangles, areas of active fires in the Algarve, Portugal. The smoke is visible in the grey/blue shades (even more apparent over sea surfaces). The area in-between is burnt vegetation.

By the time of this Aqua satellite overpass (7 August) the fires in the area had already been burning for several days. Wildfires in this popular tourist area of southern Portugal lead to major evacuations, many injuries and material loss.

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