River temperature gradients and floods
a) Central and E Canadian Arctic, W Greenland
Generally the most severe spring floods in Northern Hemi-
sphere cold-region north-flowing rivers are the result of a strong
70-85° N
temperature gradient between the headwaters in the south and
60-70° N
the downstream river reaches in the north. In these cases, the
50-60° N
spring flood wave produced by snowmelt must ‘‘push’’ down-
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stream into colder conditions, and hence towards a relatively
intact ice cover that has experienced little melting. Changes in
b) Chukotka, Alaska, western Canadian Arctic
this north to south temperature gradient would alter the sever-
ity of break up and the associated flooding.
70-85° N
60-70° N
In the future, cold season (October to May) temperatures are
50-60° N
projected to warm more at higher latitudes as compared to
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lower latitudes (Figure 8.4). The largest north to south differ-
ences are evident in East Greenland, Scandinavia and north-
c) Siberia
west Russia (region d) and Chukotka, Alaska and the western
Canadian Arctic (region b), and become particularly magnified
70-85° N
in the 2080s. This warming pattern would lead to a reduced 60-70° N
temperature gradient along the course of some major Arctic
50-60° N
rivers. If such reductions prevail during particular parts of the
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cold season, they are likely to have major implications for hy-
drologic events such as the spring snowmelt period and ice
d) E Greenland, Scandinavia, NW Russia
break up. High-latitude temperature increases are likely to lead
to less severe ice break ups and flooding as the spring flood
70-85° N
wave pushes northward.
60-70° N
50-60° N
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Figure 8.4: Average projected changes in cold-season mean
b
temperatures over Arctic land regions. The changes are broken
into three latitudinal bands for each region, as shown on the Projected temperature
small map (which has an outer rim of 50° N). Error bars repre- changes
sent standard deviation from the mean. Where greater warm-
2020
ing is projected at higher latitudes than at lower latitudes, tem-
a c
perature gradients will be reduced along large north-flowing
2050
rivers and this will likely reduce break-up severity. The reverse
2080
is true for regions where warming is most pronounced in the
southern latitudes.
d
Source: Based on Prowse and others 2006
29
206 GLOBAL OUTLOOK FOR ICE AND SNOW