The Botany of Iceland - 01.12.1945, Blaðsíða 31

THE VEGETATION OF CENTRAL ICELAND
373
not go further into this question. The registrations from Stóri Núpur
give no idea of the conditions prevailing in the highland.
B. Precipitation.
It applies to the precipitation as to the temperature that we must
confine ourselves to considering the registrations made in Möðrudalur
or at Grímsstaðir. From the former locality I have found no records
of the rainfall, and the measurements from Grímsstaðir only comprise
the summer months; they show the following figures:
May June July August September
19 27 29 34 26 mm precipitation (M 0 1 h o 1 m
Hansen 1930, p. 9).
However, according to verbal reports from the inhabitants there is
less precipitation in Möðrudalur than at Grímsstaðir, and the same
applies to the southern region almost as far as the northem edge of
Vatnajökull. The rain-bearing wind as a rule blows from the north, and
experience has shown that it often rains at Grímsstaðir when it is dry
weather in Möðrudalur. On the other hand, it may happen that near
the jökull southerly winds carry some precipitation with them. It may
be established that throughout the whole Brúaröræfi the precipitation
is low, and perhaps also the considerable wind erosion in this region
is due to this fact. In the other areas investigated conditions are quite
different. The vegetation of Snæfell and Lónsöræfi bears distinct
evidence of a fairly abundant precipitation, and the precipitation is
especially abundant in the regions Landmannaafrjettur and Síðumanna-
afrjettur in the southern part of the country. Some conclusions may be
drawn from the precipitation at Kirkjubæjarklaustur, the station lying
nearest to Síðumannaafrjettur, which proved to be as follows (mean
precipation of the years 1931-1934 measured in millimetres) :
May June July August September
65.9 114.4 95.4 146.6 181.8
As a rule it rains more in the mountains than in the lowland; at
any rate this was our experience in the summer of 1937. As an example
of the violence of the rain in these regions I may mention that at Blágil
on Síðumannaafrjettur we once registered 96 mm of rain in 24 hours.