Climate

Heligoland has the mildest climate of Central Europe, almost subtropical or almost mediterrean. Within the last 40 years the average water temperature of the North Sea has increased around about 1.98°F. In the average Heligoland has the USDA zone 9a. Comparisons between Heligoland (USDA zone 9a), Hamburg (USDA zone 8a) and London (USDA zone 8b/9a) are listed in tables below. However, the data are expressed only a little roughly, inaccuracies aren't excluded, since it's difficulty to get exact weather data of the past 20 years. However, differences are really clear. Only 2 times within the last 20 years Heligoland had "exotic endangering" extreme winters, that were the winters 1985/86 and 1995/96. Not only the minimum temperature is decisive for the winter hardiness of the "exotics", rather the duration of the black frost periods and ground freezing depth (Frost dryness risk, at all at the eucalypts and other evergreens!!!), this have years of my experiences with exotics in my garden in Hamburg/Germany shown. For example, Musa 'Orinoco' has survived 16°F in Texas, while the same variety didn't survive 14°F in Hamburg/Germany despite of the winter protection method of Musa basjoo. Only one night for some hours -16°F and 2 weeks black frost without snow cover at lowest temperatures of to 14°F, this is already a big difference! I have therefore also indicated the number of black frost periods and their respective duration of at least 3 days also besides the number of ice days. Data are red labeled if they are "exotic endangering". More than 60 frost days per winter could also endanger "exotics" and cause frost damages at them. Late frosts are also dangerous in April and May and damage the new growth and also the bark of the "exotics" by the freezing of the sap. And London doesn't know any "exotic endangering" black frost periods although the lowest temperature of 16°F, you see proofs of it in the Kew Gardens. Large old eucalyptus trees stand there, a more than 33 feet tall Eucalyptus dalrympleana stands there. The many camelias and holm oaks (Quercus ilex) are conspicuous and at the subway embankments the many Viburnum tinus, also trachys stand there unprotected and never see any winter protection, occasionally tentative even Phoenix canariensis. Jubaea chilensis and Butia capitata wouldn't have any problems there either. But the winter minimum temperatures show astonishing differences between London and Heligoland, the minimum temperatures of mildest winters are in London between 27°F and 25°F and on Heligoland however even between 30°F and 28°F. But under reservation since there also are extreme winters on Heligoland with black frost periods, if also rarer and in weakened form than in Hamburg/Germany. The difference between the winter minimum temperatures in Hamburg/Germany and on Heligoland can be between 5 and 10 degrees or more, since the North Sea being warm weakens the Sibirian cold snaps from the east.

The North Sea is an extensive heat accumulator, the water doesn't warm up in spring so fast and holds but the warmth till far into the late fall or winter and hands in it only slowly. The springs on Heligoland are cooler than on the mainland, for this the falls are warmer and longer than on the mainland. Another favoring factor is the Gulf Stream, as is well known to also warm Great Britain and Ireland, no wonder that palms also thrive there in Ireland and Great Britain, primarily in Southern Ireland, in Cornwall and on the Scilly islands.

The average precipitation sets of the winters 1996/97 to 2002/03 (respectively from Oct. 31st to March 31st) are 280 mm on Heligoland in Hamburg 299 mm and in London 260 mm. However, the details are a little inaccurately and also a little incomplete, primarily the precipitation data from London of the winters 1982/83 to 1995/96 are missing. However, it is obvious that the amounts of precipitation on Heligoland are a little smaller than this one in Hamburg. Although London shall proverbially have a lot of fog and rain, but the amounts of precipitation seem to be smaller on Heligoland anyway. The climate on Heligoland is a little drier than in Hamburg. Heligoland shows a little smaller precipitation quantities than Hamburg, it lies that Hamburg has a town climate and the air is warming faster and more strongly in the town and rises and condenses to clouds with precipitation. Also on the mainland the air is warming faster and more strongly than over the water surface of the North Sea and rises and condense to clouds. This has also explained its higher number of sun hours in Heligoland than on the mainland, this is connected with the condensation of the air and cloud formation, the sun hours aren't indicated on the table below, more infos about that under http://www.wetteronline.de.

It is often strong windy on Heligoland. 43,000 trees and shrubs were planted from 1953 to 1955, in fall 1956 were 99 percents damaged by wind! 2000 shrubs were planted again in spring 1956, these 2000 shrubs were also destroyed in fall 1958! Not only by the salty strong sea winds but also by the dryness and the low precipitations according to Mr. Neulen, the retired island gardener of Heligoland. Mr. Neulen compares the climate of Heligoland with the rock coasts of Norway, Scotland, West Ireland or Brittany.

However, the situation seems to have changed, there are right large trees and shrubs on Heligoland at places sheltered from the wind on the Upper Land and on the Lower Land now. A little deciduous wood exists on the 3000 square meters large yard of the ornithological station in a hollow on the Upper Land, exotics also could theoretically be grown there. At last I had been on Heligoland on a class journey in 1976, I still remember the old mulberry tree (Morus nigra) in the parish priest garden on the upper land, the tree should be over 180 years old and have survived all, self the bombardments in the World War II. and the BIG BANG in 1947. But right large trees and shrubs which I have seen on August 25th and 26th in 2003? However, I still remember tamarisks on Heligoland and I didn't see any single windmill palm at that time there, too. All others were planted only from the eighties, under these also "exotics", at all of them on the yard of the Mielck House.

The summer on Heligoland are similar to the in Southern Ireland. They are in moderate warm, but in Southern Ireland also are growing palms of different species and subtropical exotics, which are not sufficient hardy on the German mainland. Also Arbutus unedo (Strawberry Tree) is indigenous in Southern Ireland and might also completely hardy on Heligoland and get well with the climate there! On sunny and wind sheltered places on Heligoland in the Lower City and in the Upper City like I could feel it, the temperatures can get higher than on windy places, 86°F might be possible. The maximum temperatures given below were measured in terms of the south beach over the water. The temperatures could be higher on the island even, for example on the Upper Land or on the northeast area over the ground at sunny places sheltered from the wind, such as in the atria.

Below the more exact climate data of Heligoland of the German meteorological service from the time period 1995 to 2003, more factors have been taken into account here. We cordially thank the German meteorological service for the provision of the data. The winter minimum temperatures in the above tables only refer to the air temperatures. Ground level temperatures aren't like the air temperatures, it is in the winter always colder on the ground. The temperatures in Hamburg on the ground are at all events considerably lower than on Heligoland in the comparison.

Author: Joachim Jaeck

Updated April, 4th, 2004