Jökull - 01.01.2005, Page 123

Energy balance of Brúarjökull and the August 2004 floods in the river Jökla.
Figure 2. a) Discharge of Jökla observed at Brú á Jökuldal, 40 km north of the Brúarjökull terminus (Figure
1). b) Precipitation north and southeast of Brúarjökull. c) Temperature at Eyjabakkar 655 m. d) Measured
solar radiation on Brúarjökull compared to theoretically calculated clear-sky irradiance (Olseth et al., 1995).
The floods occurred in two events: from August 3–6 and 9–14. The daily values of precipitation in (b) are
accumulated from 9 am. GMT at day t to 9 am. GMT at day t+1, e.g. August 1–2 is from 9 am. on August 1
to 9 am on August 2 (see Table 1). Regular daily averages are used for the other parameters. – Rennsli í Jöklu,
úrkoma og lofthiti í veðurstöðvum utan Vatnajökuls og sólgeislun á Brúarjökli.
heavy rainfall reached the glaciated area of the water
drainage basin of Jökla (Einar Sveinbjörnsson, per-
sonal communication, 2005). The cyclonic weather
system advanced first from the south during August
1–2, passing the highest parts of Brúarjökull, and then
from the east during August 2–3, passing the entire
outlet area. A rain shadow is clearly seen at the low-
est elevations of Brúarjökull and north of the glacier
on August 1–2, and north and northeast of the outlet
on August 2–3. This can explain the low precipita-
tionmeasured at Kárahnjúkar August 1–3 (Figure 2b).
All this suggests that the rainfall peaked more or less
within the glaciated area of the water drainage basin
of Jökla (Figure 1). The second flood, from August
9–14, followed a period when exceptionally high air
temperatures were observed at and around the outlet
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