Jökull - 01.01.2013, Blaðsíða 81

Sensitivity of Icelandic river basins to recent climate variations
Table 5. Differences in the median or mean of various hydro-climate variables (Table 2) between wet and dry
years (∆ = Median[wet] – Median[dry] and θ = E[wet]/E[dry]). Statistically significant changes at the 10% and
5% levels are marked with a * and **, respectively. – Mismunur á milli votra og þurra ára (∆ = vott – þurrt, θ
= vott/þurrt). Tölfræðilegur marktækur mismunur miðað við 10% líkur er sýndur með * og miðað við 5% líkur
með **.
Indice / Gauging station VHM- VHM- VHM- VHM- VHM- VHM- VHM- VHM-
19 10 26 145 144 66 64 96
∆ (AT) (◦C) –0.3 –0.04 –0.5* 0.1 –0.3 0.3 0.1 0.5*
∆ (AP)/AP-dry (%) 45** 51** 41** 55** 45** 58** 41** 47**
∆ (AR)/AR-dry (%) 39** 37** 66** 34** 39** 59** 49** 58**
∆ (AWR)/AWR-dry (%) 42** 51** 41** 40** 29** 37** 35** 44**
∆ (AQ)/AQ-dry (%) 30** 35** 22** 23** 11* 23** 29** 12**
∆ (AMS)/AMS-dry (%) 62** 90** 72** 70** 70** 56** 49** 34**
∆ (DAMS) (days) 0 16 16 7 11 –6 1 –4
∆ (ASD) (days) 50** 35** 38 58** 58** 33** 38** 46**
∆ (ASR)/ASR-dry (%) 55** 66** 30** 81** 46** 59** 55** 32**
∆ (AGR)/AGR-dry (%) NA NA NA –28 –26 1 –8 –2
∆ (AGD) (days) NA NA NA –14 –14 5 6 16
∆ (CTS) (days) 14 7 22 7 14** 9 –14 –10
∆ (CTW) (days) 18 3 17 7 6* –11 –12 –20
∆ (CTQ) (days) 12 13 –7.5 14 21** 2 –5 –17
∆ (AMF)/AMF-dry (%) 0 4 16 17 10 44* 31** 44**
∆ (DAMF) (days) 102 –99 5 9 15* –39 –3 –35
∆ (SMF)/SMF-dry (%) 7 –8 12 17 10 15* 12* 44**
∆ (DSMF) (days) 11 –11 5 9 15 0 –59 –39*
θ (FOR): POT-3 1.6 1.9** 1.6* 1.8 * 1.2 2.2** 2.5** 3.1**
θ (FOR): POT-2 1.4 1.7 1.4 2* 1.9* 2.7** 3.9** 3.6**
creasing temperature in two partly-glacierized catch-
ments, one located in the south and one in the west.
A decrease was observed in the northeasternmost
catchment, while there was no change in the others.
The flood occurrence rate (FOR) above the moderate
threshold (POT -3) remained mainly unchanged be-
tween warm and cold years at most catchments, ex-
cept for two catchments in the west and south (VHM-
66 and VHM-96) where an increase was observed
in warm years. For the higher threshold (POT -2)
the increase in warm years extended to a third catch-
ment located in the southwest (VHM-64). The in-
crease of flood occurrence rate in warm years in these
basins is probably related to more abundant rainfall
and snowmelt events in winter and spring.
Hydrological response to precipitation variations
The hydrological response to precipitation variations
was examined by comparing wet and dry years. In
wet years, the median annual precipitation was ap-
proximately 40 to 60% larger than in dry years (Ta-
bles 3 and 5). As a consequence, a significant in-
crease of annual rain was observed for all catchments.
The annual snowpack peak magnitude (AMS) also in-
creased everywhere, but its timing (DAMS) remained
unchanged. A significant increase of annual snowmelt
runoff and an extension of the duration of the snow
cover period were also found. No significant differ-
ences in the annual glacier melt runoff nor in the du-
ration of the glacier melt period between wet and dry
years were found. Annual rain and snowmelt runoff
increases in wet years caused a significant increase of
annual mean total water input runoff (AWR) and an-
nual mean streamflow (AQ). Center of volume dates of
snowmelt (CTS), total water input (CTW) and stream-
flow (CTQ) did not differ much between wet and dry
years.
JÖKULL No. 63, 2013 81