Our fellow Dutch climate blogger and friend Klimaatgek writes about how cold this spring has been in the Netherlands this year, namely April and May.
Not long ago I reported how Germany had seen its fourth coldest April since recordings began in 1881. May so far hasn’t been warm either as the DWD German weather service reported the first 15 days had been the 7th coldest since 1881. The forecast sees more cool and wet weather for the rest of the month.
Now our Dutch friends report on April and May temperatures in the Netherlands:
In the May 5, 2021 post, I wrote about the remarkably cold April month of 2021. The May 17 post was about how a weatherman tried to downplay that very cold April month with the help of a curious little map.
To show how remarkably cold the past April month was, I made three charts: (Tg = average 24 hrs; Tn = min.; Tx = max.):
Fig. 1 Data: KNMI
The graphs are based on 24-hour temperature data for De Bilt. As you probably know, these temperature data were homogenized between 1901 and September 1951. This homogenization is controversial, as has been written about here before. I used these corrected data to make the above graphs but will indicate further on how the raw measurement data differ from this.
Figure 1 shows the average Tg of the month of April from 1901 through 2021, Tg is the average 24-hour temperature. Tg of April 2021 is shown in red. I did the same in Figure 2 but with Tn, the minimum daily temperature, and in Figure 3 with Tx , the maximum daily temperature of April. In all three figures, the cold month of April 2021 can be clearly observed. It is striking that especially the average Tn (minimum temperature) of April 2021 is very low.
Because the current month of May is also very cold, I also made charts for the month. Since the temperature data for May 21 to May 31 are not yet known at the time of writing, I have used the KNMI forecasts for Tn and Tx and the Weerplaza forecasts for Tg.
It’s a similar story for May: May 2021 is remarkably cold in the series since 1901. The difference with April is that the May 2021’s average Tx (maximum daily temperature) is remarkably low.
To find out whether the homogenization applied by KNMI to the temperature data from De Bilt affects the above picture, I also examined the raw, uncorrected data for April and May. For both the homogenized and the raw data, I calculated the position of April and May in the total series of April and May from 1901 to 2021:
For Tg, Tn and Tx of April and May respectively, using the homogenized data on the left, I calculated how many years were colder than 2021 and how many were warmer than 2021. The picture is clear: April and May 2021 are remarkably cold for the 121-year period.
The right side of the table shows the figures after you apply the raw, uncorrected data from De Bilt. Based on raw data, both April and May 2021 rise a bit further in the ranking of coldest months.
Is all this a sign that we are at the beginning of a cooler period? Maybe so, but it’s hard to draw any firm statements about that I think.
In any case, it shows that the moment you think there is a real trend in the works after a few years of striking heat (and drought), you suddenly find yourself back to reality.
Except for alarmist weathermen, of course.