Geoscience Reference
In-Depth Information
Figure 6.15.
Number of gauges in the R-ArcticNET database through time and the
percentage of the drainage area monitored. Data are shown for North America, Eurasia,
and the Arctic drainage as a whole. Only gauges monitoring an area greater than 10,000
km
2
are used for the percentage of area monitored (adapted from Lammers et al.,
2001
,
by permission of AGU).
discharge to the Arctic Ocean on an annual basis. The Lena, the Ob, and the Yenisei
alone contribute on average 57 percent of the total discharge.
6.5.3
Surface of Mean Annual Runoff
Recall that runoff is discharge divided by the catchment area. It has units of water
depth. Gauge data can be used to construct surfaces of runoff.
Figure 6.16
is the
mean annual runoff surface over the January 1960 to December 1989 period for the
monitored part of the Arctic drainage. Following N. Arnell (
1995
), calculations of
runoff were made for all “interstation areas.” These were obtained by subtracting all
upstream discharge values from the discharge value at the next downstream gauge.
Runoff was then calculated by dividing the interstation discharge by the intersta-
tion drainage area. The monthly interstation runoff values for each gauge were then
distributed to the interstation regions to provide a gridded field.
The spatial resolution of the runoff surfaces that can be obtained depends on
the density of the gauge network, which varies greatly. For large interstation areas,
inconsistencies can be introduced because of the long transit time of water moving
downstream in the river system. Flow diversions and impoundments (dams and irri-
gation channels) can significantly alter the natural drainage. Known problem areas
include the Nelson/Churchill rivers in western Canada, the La Grande hydroelectric
