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Spring in Germany arriving later and later every year. Also forsythia blossoms in Hamburg arriving later and later

By Josef Kowatsch und Stefan Kämpfe

[Translated/edited by P Gosselin]

This is an addendum to our earlier article on delayed spring blossoms here (and here at NTZ).

In our previous article linked above we showed that mean temperatures for the months of January, February and March have been cooling for almost the past three decades, this according to the German DWD National Weather Service. And this is the result without applying any urban heat island adjustments to the measured temperatures.

As a result we are seeing increasingly delayed spring starts – especially spring blossoms in open areas where the cooling is even more pronounced. We confirmed this with our own vegetation observations in the article, e.g. the blossoming of winter aconites out in the open.

Crocuses and winter aconites; Photo by J.Kowatsch/Stefan Kämpfe

Some readers from the over 100 comments left cast doubt on our observations, and pointed out that the official authorities such as the State Office for Environmental Protection in Karlsruhe or the DWD claimed the opposite was in fact occurring, i.e. spring was arriving earlier and earlier. However these readers failed to provide any measured data from these officials.

We took the time to look more deeply into the matter and found something astonishing. The State Environment Office in Karlsruhe itself does not even keep any such long-term observations. Instead it gets the results from the DWD. And the DWD appears to have the habit of regularly citing forsythia blossoms in the City of Hamburg as an example of spring arriving earlier. The blossoms are earlier and earlier, the DWD claims, at least those that the DWD always likes to invoke. This claimed early blossoming indeed must be evidence of climate warming, a few of the readers believed.

Well, a former DWD employee recently provided us with the following diagram of the forsythia blossoming data for the Hamburg Lombard Bridge from the DWD itself. The surprise is great:

Fig. 1 The left side vertical axis depicts the number of days after the start of the year. The higher the number, the later the start of forsythia blossoms. The chart shows they are arriving almost 20 days later than 25 years earlier.

Although the observation series were recorded right in the middle of heat island Hamburg, and thus did not even fulfill the conditions for an objective observation, the start of blossoms turns out to be precisely as those in the completely open exposed areas that we looked at in our previous article: Since 1988 spring has been arriving later and later. The start of springtime forsythia blossoms is also arriving later and later in the large urban heat island of Hamburg.

Result: Also the data on the City of Hamburg show that forsythia blossom have been arriving considerably later and later since 1988, indicating a increasingly delayed start of spring.

The constant claims that forsythia blossoms are coming earlier and earlier are false.

Another phenologist located in Seesen also sent us his observation data of forsythia blossoms, and these are shown in the following chart:

Fig. 2. Forsythia blossoms have been arriving later and later also in Seesen for the past 28 years. The observations are consistent with the data from the DWD in Hamburg.” Data source: Phenologist Georg v. Petersdorff-Campen

Result: Spring in Germany is beginning later and later. All March blossoms are delayed. We trace this back to the months of January, February and March becoming colder and colder over the past 28 years.