Jökull - 01.01.2013, Síða 79

Sensitivity of Icelandic river basins to recent climate variations
Table 3. Median annual temperature, AT (◦C), precipitation, AP (mm/year) and streamflow, AQ (m3/s), for the
various subsets. – Miðgildi árshita, AT (◦C), ársúrkomu, AP (mm/ár), og ársrennslis, AQ (m3/s), fyrir mismun-
andi áraflokka.
Variable / Gauging station VHM- VHM- VHM- VHM- VHM- VHM- VHM- VHM-
19 10 26 145 144 66 64 96
AT (1971–2000) –0.1 0.2 0.6 –1.2 –1.8 –0.8 0.9 –0.6
AT-warm 0.5 0.7 1.2 –0.6 –1.2 –0.2 1.6 0.2
AT-cold –0.9 –0.5 0. –1.7 –2.4 –1.4 0.3 –1.0
AT-wet –0.2 0.4 0.5 –1.1 –1.8 –0.5 1. –0.3
AT-dry 0.1 0.4 0.9 –1.3 –1.5 –0.8 0.9 –0.8
AP (1971-2000) 2996 798 1291 851 1061 1634 1978 1683
AP-warm 3227 845 1269 774 956 1943 2283 1894
AP-cold 3035 826 1316 875 1147 1645 1975 1560
AP-wet 3672 996 1488 1056 1248 2141 2477 2246
AP-dry 2539 658 1059 680 861 1358 1763 1530
AQ (1971–2000) 3.0 10.5 13.6 20.6 38.3 79.6 369.5 80.2
AQ-warm 3.4 9.5 12.8 22.9 40.4 88.0 404.8 86.2
AQ-cold 3.0 10.2 14.4 21.1 38.9 74.4 364.6 76.7
AQ-wet 3.6 11.9 14.4 22.8 41.4 88.0 433.8 87.8
AQ-dry 2.7 8.8 11.8 18.6 37.4 71.3 336.1 78.4
ical variable between warm and cold years. The me-
dian annual temperature increase of 1.1–1.4 ◦C was
accompanied by a significant increase in rainfall in
west and northwest Iceland due to a change in the
fraction of liquid and solid precipitation while precip-
itation remained unchanged. Rainfall also increased
in the south, in association with both temperature
and precipitation increases but remained unchanged
in the northern and northeastern catchments. The an-
nual snowpack peak magnitude (AMS) was reduced in
warm years in the majority of catchments and its tim-
ing (DAMS) was shifted several weeks earlier, for five
catchments.
In response to higher temperatures, the annual
snow cover duration (ASD) was shortened by several
weeks in all catchments but one. Annual snowmelt
runoff (ASR) was significantly lower in warm years
at three elevated catchments for which the magni-
tude of the annual snowpack peak decreased, but
remained unchanged for the other watersheds, even
for those where the magnitude of the annual snow-
pack peak decreased. The annual glacier melt runoff
(AGR) in the warm years was 20 to 40% larger than in
the cold years for all the glacier-covered catchments.
Where annual precipitation remained unchanged, the
increased glacial melt indicates loss of mass through
ice melting from glacier ablation areas and/or firn
melting from glacier accumulation areas. Increased
glacier melting was associated with longer glacier
melt period (AGD) by several weeks in all glacierized
catchments.
Annual total water input runoff (AWR) was not
affected by temperature variations in the northern
and northeastern glacier-free basins, because rain and
snowmelt remained unchanged. A significant AWR
increase was observed in warmer years in the north-
western catchment VHM-19, most likely because of
increased rain. The increase in AWR with higher tem-
peratures in the western and southern glacier-covered
catchments (VHM-66, VHM-64 and VHM-96), was
probably due to a rainfall increase, re-enforced by
a larger glacier melt runoff. For the two northern
glacier-covered catchments (VHM-144 and VHM-
145), AWR did not change, although glacier melt
runoff increased, indicating that the increased glacial
melting was not large enough to compensate for the
decrease of runoff on the glacier-free part of these
watersheds. Annual mean streamflow (AQ) increased
JÖKULL No. 63, 2013 79