Weather in Ghent

Wednesday 5 October: Did we have a heatwave in Gent during summer 2016?

Summer is really over now, time to look back. Both in July, August, and September the temperature sometimes peaked at tropical values over 30°C. Belgium registered an offical heatwave from 23/08 till 27/08. But did we experience a heatwave in Gent based on our measurements?

Temperature summer 2016 — Temperature evolution (10-min averages) during July, August, and September 2016. We recognize 3 warm periods (around 20/07, 24/08, and 13/09). The warmest outliers are measured at the Provinciehuis (red), Sint Bavo (yellow), and Honda (green). The lowest nighttime temperatures are registered in Melle (black), Wondelgem (blue), and the botanical garden (purple). The vertical ligns are caused by some missing data.

Each country is using different heatwave criteria. This does not come as a surprise, a hot period in Brussels may be classified as normal in Sevilla. The RMI defines a heatwave for Belgium as a period of at least 5 consecutive days with temperatures peaking over 25°C including at least 3 days over 30°C, measured in Ukkel. The KNMI is using the same definition but with the De Bilt data. In what follows we apply these criteria for the Gent data of the 2016 summer.

For the period 23/08-27/08 the Ukkel measurements fulfilled the criteria for a Belgian heatwave. This is exceptionally late in the summer season. Below the measurements of the Gent stations for the period 22/08-28/08 are shown. For 5 out of the 6 stations the criteria for a heatwave are met, only for the Melle station no heatwave is registered. On 5 days the temperature exceeded 25°C in Melle, but there were only 2 tropical days. With a maximum temperature of 29.6°C on 27/08 in Melle, it was however a near miss.
For the botanical garden, Honda, and Sint Bavo the heatwave lasted for 5 days (23/08-27/08). The botanical garden was an edge case with a third tropical day peaking at only 30.2°C on 27/08. For Wondelgem the heatwave continued till 28/08 and at the Provinciehuis it started already on 22/08 making it a 7-day event. The highest temperature measured during the event (and during the whole 2016 summer) was 34.5°C on 25/08 in the port at the Honda location.

Temperature heatwave august 2016 — Temperature evolution (based on 10-min averages) for the 22/08-28/08 period. At the 5 urban locations a heat wave was registered whereas in Melle the criteria for a heat wave were not satisfied (maximal temperature of only 29.6°C on 27/08)

It is important to realize the limitations of such a definition, details can make or break a heat wave. As an example consider the following maximum temperature series in Melle and the botanical garden:

23/08 : Melle = 29°C --- Botanical garden = 28.6°C
24/08 : Melle = 32.7°C --- Botanical garden = 32.7°C
25/08 : Melle = 33.1°C --- Botanical garden = 32.9°C
26/08 : Melle = 27.1°C --- Botanical garden = 26.3°C
27/08 : Melle = 29.6°C --- Botanical garden = 30.2°C

Although Melle is on 4 out of the 5 days at least as warm as the botanical garden and its average maximal temperature is higher, we do register a heatwave in the botanical garden while there is none in Melle.

Conclusion
The 5 weather stations situated at the urbanized locations did register 1 heatwave during summer 2016. For the rural Melle location the criteria were not met.