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Which Dutch city centers suffer the most from heat islands on hot summer days? This series tries to find an answer to this question with the help of the ECOSTRESS data provided by NASA, where ground temperature data in areas measuring 70 by 70 meters can be sought. Recently, these super-local measurements are also available for the Netherlands. A new episode is published every Tuesday and Friday, with three new city maps every time. Read the other episodes of this series here.

Where are the heat islands in Dutch inner cities? With this question and a whole heap of cartographic fireworks, the editor on duty first set to work on this column late last August. Two months later, 26 Dutch inner cities have been put under the microscope and this series has come to an end for this calendar year. Of course, a summer column like this does not match up very well with the chilly weather ahead of us this November. But either way, that the city of Maastricht had the least inner city heat stress of all of the Netherlands is pretty clear.

In this final episode, we look back through some of the rankings and classifications. We will begin with the two city centers that were the best of all in terms of withstanding the heat, according to the ECOSTRESS satellite data. Then comes the coolest residential areas and the hottest environments that we came across. And finally, the fence-sitters of the Dutch heat stress test. All analyses used the very sunny and hot weekend of Aug. 12 and 13 as the benchmark. This is what the KNMI weather maps looked like at that time.

Why specifically this particular weekend? Because NASA’s antennae were pointed in just the right direction on this sun-drenched afternoon and it was tropically hot throughout the Netherlands, even as far as the coast. Ideal conditions for these kinds of measurement, also for cross comparisons and rankings. At the end of this coloumn, we have listed all 26 cities in the final ranking. But first, the outliers, starting with the two inner cities that withstood the sweltering summer heat the best.

Heatproof capital city

Despite the crowded streets, our capital city is superbly shielded against the scorching sun. Thanks to its monumental ring of canals, it hardly gets more than 45℃ anywhere on the ground surface in Amsterdam. Only one other inner city managed to stay below the median temperature of 40.8℃ on the surface of this historic tourist attraction.

Here, extreme heat only ever occurs on flat roofs of large complexes such as the Ziggo Dome. In episode 9 & 10 the entire city is mapped out with the help of six such high-resolution visualizations. How does 020 (the telephone prefix for Amsterdam) stay relatively fresh during tropical periods? Water. Lots and lots of water. Not only thanks to the canals, but thanks to the adjoining IJ as well. This is not just the case in the center, by the way.

Due to its location in the western part of the country, it gets far less hot here than further inland. If this were a game, then Amsterdam would be playing this heat stress test at level easy. Still, the No. 1 ranking shows that this need not be a problem at all.

The coolest in all the country

Anyone eager to visit heat islands would do best to avoid downtown Maastricht. The Limburg capital kept its head cool. Nowhere in the center did it get hotter than 43.6℃ on the cobblestones of the Markt, according to NASA. This is more than the freshest locations of the stragglers in the rankings featured at the end of this story.

Maastricht, like Amsterdam, also benefits from a fair amount of water. Except here, it’s not so much canals. This is where the meandering Meuse River acts as a natural air conditioning system for the surrounding areas. When the editor on duty had a look at this city’s data, his first thought was that he had made a mathematical error, or that the algorithm was having an off day. This turned out not to be the case after checking it three times.

While the KNMI station down the road was reporting 31.9 ℃ at a meter-and-a-half above a grass field, the modal ground temperature in downtown was about 8.8℃ higher. This sounds steep, but is actually fairly modest. Elsewhere, this figure easily rises toward 12-13℃. Relatively many green areas can be spotted on the map. Thanks to the numerous public green spaces, no one at all has to sweat themselves to a frazzle during an outdoor concert of André Rieu at the Vrijthof.

Bastion Bergkwartier

When subjected to heat stress, things typically heat up about five to ten degrees more inside built-up areas than outside them. Yet there are also several residential neighborhoods where the ground warms up only a few degrees more than the air. The map above shows Amersfoort’s Bergkwartier district, a very green pre-war neighborhood, located a stone’s throw from the train station and the city center, where the convenience of the city and the comfort of the countryside converge.

Amidst the many trees on the ‘Berg’, it barely gets hotter than 38 ℃. That’s only seven degrees more than the meteorologists in De Bilt reported at a meter-and-a-half above a grass field. The mystery of that remarkable blue spot on the map of Amersfoort is unraveled rather quickly after a quick peek at Google Street View. Now and then a huge mansion of a home with a huge patch of land. But mostly trees. Lots and lots of trees.

Other examples of residential neighborhoods where the ground surface remains wonderfully cool under the bright sun are Berg & Bos (Apeldoorn), IJburg (Amsterdam), Noordereiland (Rotterdam) and Zuiderburen (Leeuwarden)

A completely different situation is found at the back of Utrecht Central Station…

Hot, hotter, hottest

You won’t get a clearer picture of heat islands in the Netherlands. The Jaarbeurs and adjacent parking lots form a bright red oil slick on the map of Utrecht. Readings of 50℃ or higher usually only show up on furniture boulevards and industrial areas.

Yet the hottest spot of all has been held firmly since the third episode in the mournful Jaarbeursplein, where – on a flat dark roof – it got up to 55.5 ℃ on Aug. 13. Temperatures are also slightly higher in the surrounding residential areas owing to the influence of this heat magnet of stature, where, to compensate, ample parking can be found. This is what the national Top Ten looks like:

Four business parks with warehouses and business premises in concrete blocks, three indoor event halls, two factory complexes and a furniture boulevard. It is striking how prominently Breda is represented in this list, while the West Brabant city scores rather unremarkably in other areas.

#03 - De Krogten (side of hell), Breda

Blisteringly hot city center

Apeldoorn, perhaps the most village-like big city in the Netherlands. You would not think it, but almost 180,000 people live in this sleepy town, which is beautifully located by the Hoge Veluwe. Julianatoren (36℃), Paleis 't Loo (37℃), the Apenheul (33℃). Conditions here remain pleasant even on the hottest days of the year. However, this is not the case everywhere.

As the previous paragraph did make clear, the very highest values are measured in barren business parks on the outskirts of the city. However, this is not the case in Apeldoorn. In fact, the big red spot in the middle is the city center and in particular the shopping streets. Does the municipality sometimes think that trees or city parks are not needed anywhere with the largest park in the Netherlands so close by?

With a median of 44.8℃ and 48.5℃ in the narrow shopping streets, it is on average 4℃ warmer here than in Maastricht. The difference from the walking trails of the Apenheul in the far west of the map runs as high as 15 ℃. Nevertheless, it is not quite enough to snare the dubious title.

Hot spot Hengelo

Enschede has proudly led the hot spot rankings since the beginning of this column. Yet after the Twente episode - which used another measurement point in time of a more qualitative nature - this turned out to be a bit off. The most sweltering city center in the Netherlands is about 10 kilometers away in Hengelo, where a hot summer seems to have almost free rein. Is 50℃ only possible in tucked-away business parks? Not at all. Shopping center Thiemsburg is proof to the contrary.

With 45.3 ℃ as median ground temperature and 48-49℃ in a number of shopping streets, humble Hengelo has managed to establish a more serious city center heat island than any of the major cities that we covered earlier. That serious work needs to be done on this, by the way, has been known for some time.

With large-scale renovation, a revamped town square and more space for art and greenery, the municipality aims to once again become the metaphorical hot spot of the Eastern Netherlands. Whether this will cost them the trophy as a literal hot spot, time will tell. Unfortunately, they won't be able to take advantage here of a wide river or a 17th century network of canals to keep heat stress under control. At any rate, the marketplace needs to be a lot greener

The spine-chilling final score

Has your favorite city not yet been featured in this article? If so, chances are it's a middle-of-the-pack city. Here are some rankings that examine inner-city heat stress in different ways, i.e.: median, highest outlier and the difference with maximum temperatures

The median indicates the temperature that is exactly in the middle in terms of altitude. The choice was made for this to avoid high peaks and troughs in the totals. District and neighborhood data from CBS made it possible to link the NASA figures to a specific area. The most right-hand column shows the hottest 70-by-70-meter patch within this boundary.

Mediaan of verschil KNMI?

While the median already says quite a lot, the above table is still a bit like comparing apples to oranges. After all, it was not exactly the same temperature everywhere in the Netherlands. This has been taken into account in this second ranking, so a number of eastern cities where it was slightly warmer on those days do appear in the upper regions.