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CLIMATE.
45
marked, if we compare the rainfall during the months of May and August;
in Gottland, for example, the average precipitation during May amounts
to only 25 mm, while in August it varies between 50 and 65 mm.
Winds. The cyclones arriving in Northern Europe from the seas to
the west pass, as a rule, right across Sweden or to the north of the country,
this explaining the predominance of south-westerly winds and the mild
winter climate of Sweden, as well as the somewhat frequent occurrence
of the storms that sweep over Swedish waters. According to the calculations
of wind-velocities made at the lighthouses, there occur yearly, on an
average, 20 storms on the west coast of Sweden, 11 on the south coast,
23 off Gottland, 8 in the Sea of Bothnia, but only 2 in the Gulf of
Bothnia. These storms, although a hindrance and a danger to navigation,
cannot, however, be compared with the hurricanes occurring in tropical
waters. In 1905, storm-warnings began to be sent from the Central
Meteorological Office to 28 stations on the west coast of Sweden. This
was a step taken in collaboration with the Board of Agriculture for the
assistance of the fisheries and, at the request of the fishermen, additional
stations were opened during the course of the next few years, and the
system was extended to the southwest coasts of the Kingdom. In 1913
the total number of storm-signalling stations amounted to 47, and in
the same year the Riksdag made a grant for the purpose of extending
the system to the east coast, too. The warnings in question are issued
both for high winds and gales (windvelocity at least 14 m per second,
or 7 Beaufort), the velocity now mentioned having occurred, on an average,
80—100 days yearly at one storm-signalling control-station on the west
and south coasts, while gales (windvelocity not less than 20 m per second,
or 10 Beaufort) have occurred there only some 10 days yearly per
station.
As regards the interesting but difficult question of the secular alterations in
our climate, it appears from botanical and geological investigations of the
plant-fossils occurring in the peat-mosses of Sweden, that the climate some thousands of
years ago was nearly 2° C. warmer than it is at the present day. But
historical evidence gained during the last thousand years seems to point to a change
of climate during that period, consisting of a gradual decline in the severity of
the winters. This seems to be confirmed by the descriptions given in the
mediaeval chronicles of the ice-conditions in the Scandinavian seas, and also by
the meteorological observations carried out by the famous Tycho Brahe in the
island of Yen, during the period 1582—97, as compared with those made at
later times down to the present day. It is remarkable that no severe winter has
occurred in Southern or Central Sweden since the hard winter of 1892—93.
In North Sweden, too, since the year last mentioned, the winters, as a rule,
have been less severe than those during the years 1859—93. In consequence,
the winters, on an average, have become somewhat shorter, and the mean
temperature higher than for the period 1859—93. As regards the summer, the
absence of thermometrical observations before the middle of the 18th century
leaves us in ignorance, but since that time, observations made at Lund,
Copenhagen, and Stockholm, point to the summers having become somewhat cooler.
Measurements of the rain- and snowfall commenced at the same time as obser-
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