Jökull - 01.12.1991, Blaðsíða 16

Fig.16 : Annual temperature 1901-1990 at Reykjavík and Akureyri.
Mynd 16: Arshiti einstakra ára 1901-1990 í Reykjavík og á Akureyri.
erable during this century. Low temperatures were
prevailing the first two decades, then a sudden rise
was experienced and an unusually warm period
1926-1946 followed. After 1946 a gradual deteriora-
tion started, though with two distinctive cool periods
in some parts of the country as will be described in
some detail later.
Table 2 shows, for the 7 weather stations already
in operation 1901, the 5 highest and lowest annual
temperature values during the period 1901-1990.
According to Table 2 the amplitude of annual tem-
perature variations is quite variable, i.e. the warmest
and coldest years are not the same at all stations. It is
of interest to note that most of the warmest years
occur within the period 1933-1946 and it is also sur-
prising that in southwestern Iceland (Reykjavík,
Stórinúpur/Hæll) three of the five coldest years
occurred during the last decade, i.e. in 1979, 1981
and 1983. In northem Iceland most of the coldest
years were in the two first decades of the century.
Fig. 16 and Table 2 raise the question whether it is
possible to divide the period 1901-1990 into distinct
shorter periods, warm or cold. A sudden change
from coldness to warmth is for instance fairly clear
just after 1920. In some cases such changes are well-
marked in some parts of the country but rather vague
in others. Based on the annual temperature at the 32
selected stations the author proposes the following
division for further discussion:
1901-1925
1926-1946
1947-1952
1953-1964
1965-1971
1972-1990
It is a question whether the cool period 1947-1952
should be one of the chosen ones, as it is only distin-
guishable in some parts of the country and as a matter
of fact only in two of the four seasons as will be men-
tioned later. Secondly the cold period 1965-1971 is
most pronounced in northern and eastern Iceland
where sea ice or at least cold water appeared fre-
quently near the coast during those years.
The greatest difference is found in the contrast
between the very cold period 1901-1925 and the
unusually warm period 1926-1946, which probably
is, from a climatic view, the most favourable period
since the first centuries of the settlement of Iceland
(9th - 12th centuries). It is interesting how sudden
the change is from the cold one to the warm period.
A gradual decrease in temperature starting in 1947
has generally continued until present with the excep-
tion of the two cool, discernible periods already
mentioned, 1947-1952 and 1965-1971. This is clear-
ly seen in the curves showing overlapping means.
Figs.17-18 present 5-year and 15-year overlap-
ping means of annual temperature for the three
weather stations, Reykjavík, Akureyri and Teigar-
14 JÖKULL, No. 41, 1991