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and between each scenario and observations. However, in terms of the geographical dis-
tribution of relative change or deviation intensity, divergence is not necessarily expected; if
such divergence in relative intensity prevails, it presents a main challenge for geographical
monitoring prioritization, as discussed further in Sect.
6.3
.
2.2 Arctic Hydro-Climatic Change
Precipitation output from GCMs is used to further model other hydro-climatic changes,
most importantly runoff changes, at regional and finer scales. The usefulness of precipi-
tation projections for adaptation planning, such as dimensioning of infrastructure and
drainage systems, depends on this modeling and understanding of how the precipitation
changes are (and have previously) transferred to runoff and other hydro-climatic changes
in the landscape. We therefore here investigate how recently observed precipitation
deviation has related to runoff deviation for 13 major basins where runoff data are
accessible for 1961-1990 and 1991-2002, and compare these data on runoff deviation with
corresponding observations of precipitation deviation from the CRU TS 2.1 database.
To gain a more comprehensive understanding of total freshwater flux changes in the
Arctic system, we also perform an integrated assessment of freshwater inflow from both
rivers and glaciers to the Arctic Ocean. Separation of the freshwater flux contributions
from rivers and glaciers is here possible because the glaciated area of the major Arctic river
basins is very small. Instead, glaciers and ice caps mostly contribute their melt water
directly to the coast or through smaller watersheds. For the river component in this ana-
lysis, we therefore consider only major basins with negligible glacier area that drain to the
proper Arctic Ocean with a discharge of at least 10 km
3
/year. This drainage is a subset of
the whole PADB and includes 17 basins, of which 11 (green basins in Fig.
1
) are in
common with the 14 major basins (green and blue basins in Fig.
1
) in the GCM com-
parison discussed above, and the remainder are additional smaller river basins (red basins
in Fig.
1
). We specifically investigate the periods 1961-1992 and 1993-2006, with the
period break coinciding with a marked increase in glacier mass loss. We combined dis-
charge data from the R-ArcticNET (Lammers et al.
2001
), ArcticRIMS (
http://rims.unh.
data consist of data on annual direct mass balance observations carried out for mountain
glaciers and ice caps (MG⁣ marked with crosses in Fig.
1
; Dyurgerov and Meier
2005
;
Glazovsky and Macheret
2006
; Fluctuations of Glaciers (FoG)
2008
), and of several recent
modeling studies for the Greenland ice sheet (GRIS; light blue in Fig.
1
; Rignot et al.
2008
;
Hanna et al.
2008
,
2009
; Box et al.
2006
; Mernild et al.
2009
).
2.3 Pan-Arctic Drainage Basin Monitoring
Observations of discharge on various scales allow testing of water budgets, both for
different landscape types and for the land surface area in general, which is useful in
evaluating model assumptions and parameterizations. Water chemistry observations give
information on upstream sources, sinks and hydrological transport pathways of biogeo-
chemical constituents, and their changes. We therefore also synthesize and evaluate all
accessible discharge and water chemistry data for the PADB. The extent of accessible data
is presented in map form, illustrating the maximum length of time series and latest data
year for the PADB. We further summarize the characteristics of monitored and unmoni-
tored areas in North America, Europe and Asia and compare the differences between them.
