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Ghent University studies urban micro-climatic differences within Ghent

Tuesday 22 November: Discussion of a windy Sunday: significantly less wind in the city


After a hesitating start (with a Summerlike September) Autumn now started for real. This was highlighted by the very windy Sunday of 20/11. Let us look back to this day.

On Sunday 20/11 a small low pressure system moved from the French Northsea coast over the Channel towards Denmark. Although we merely received any precipitation from the system, we definitely experienced its wind field. Below the evolution of the average wind speed (averages over 10 minutes) is shown for this day. We clearly see an increasing southern wind during the morning hours, reaching its maximum around 10 UT in the Gent region.

The differences in the average wind speed between the measurement locations are striking. In Melle the 10-minute average value peaked above 40 km/h whereas the stations in the city did not exceed 20 km/h. At the Provinciehuis it is even difficult to see any wind speed increase at all. Same conclusion for the wind gusts. Melle registered a wind gust of 80 km/h, the botanical garden peaked at 62 km/h but the stations Wondelgem and Provinciehuis did maximally reach 38 km/h and 28 km/h respectively.

Average wind speed 10/11/2016 Average wind speed 10/11/2016
Average wind speed (over 10 minutes) measured on Sunday 20/11/2016 (from midnight till midnight). Remark the significant differences in wind speed between the rural location of Melle and the urban measurement stations.
The surface roughness is responsible for this difference in wind speed. In the city there are many obstacles, e.g. buildings, reducing the wind speed close to the surface. In Melle we have an open surface with far less friction, permitting the wind to reach higher values. The precise location of the station with respect to the buildings will have an influence on the wind speed, but the trend is clear. In general the average wind speed and the wind gusts are strongly reduced in an urban environment. Similar conclusions were found in earlier studies.

Finally one should realize that these wind measurements are done at 2 meter height whereas WMO prescribes 10 meter height. At a height of 10 meter somewhat higher wind speeds will be measured but the observation height would not change the urban-rural contrast.