Geoscience Reference
In-Depth Information
1 Introduction
A multitude of global changes, including climate change, are currently transforming the
Earth system. This is clearly evident in the Arctic, where surface temperatures over the last
half-century have increased at a rate of 50 % higher than the Northern Hemisphere average
(McBean et al.
2005
), and where future climate change is expected to be the most pro-
nounced (Kattsov et al.
2005
). Coupled to the changes in the physical environment, the
Arctic is also increasingly becoming a focal point of economic and geopolitical interest.
These transformations present a considerable challenge. The critical role of the Arctic in
the global climate system implies that Arctic changes will have far-reaching consequences
for, and feedbacks to, the entire Earth system (McGuire et al.
2006
). For the Arctic region,
in turn, global-scale changes, regional and local environmental changes, and geopolitical
and economic changes all contribute to the societal need for adaptation, and to the need for
information and monitoring to guide that adaptation (Azc´rate et al.
2013
).
As an integrating, propagating and regulating factor, water plays a central role in the
changing Arctic and the wider global climate system. It is a shared component in the most
recognized Arctic indications of global change. These indications include rapidly dimin-
ishing extent of sea ice (Comiso et al.
2008
; Stroeve et al.
2012a
), increased mass loss from
glaciers (Kaser et al.
2006
; Gardner et al.
2011
), increasing river flows (Peterson et al.
2002
,
2006
; McClelland et al.
2006
; Shiklomanov and Lammers
2009
; Overeem and
Syvitski
2010
) and increasing groundwater contribution to those flows (Smith et al.
2007
),
permafrost degradation (Hinzman et al.
2005
; White et al.
2007
; Lyon and Destouni
2010
;
Brutsaert and Hiyama
2012
), ecosystem regime shifts (Smol et al.
2005
; Karlsson et al.
2011
), and shorter extent of snow cover season (Brown et al.
2010
; Callaghan et al.
2011
).
All these constitute water changes, some of which are fundamentally caused by the
overarching driving force of climate change. Some water changes, however, may also arise
due to direct human interference, for example, through freshwater abstractions for or losses
by food and energy production (Destouni et al.
2013
), or clear-cutting of forests (Seitz
et al.
2013
). Whether the driving forces are local or global, water changes require local
adaptation, for example, of infrastructure for energy, transport and buildings, of agricul-
tural and forestry practices, and of measures for food and water security (Nilsson et al.
2013
).
A primary information basis for projections of large-scale climate change is the
ensemble of general circulation models (GCMs) that underlie the assessment reports of the
Intergovernmental Panel on Climate Change (IPCC). The two most recent full reports are
the Third Assessment Report (TAR; 2001) and the Fourth Assessment Report (AR4; 2007).
The fifth IPCC report (AR5) is currently being released, with the first working group
contribution published in September 2013.
The performance of GCMs in the Arctic has been the subject of extensive discussion.
Assessments of TAR and AR4 model performance have shown improvements between
successive generations of models, but also indicated that significant shortcomings remain
in simulating observed climate parameters (Christensen et al.
2007
). There have been
several assessments of simulations of sea ice processes (Zhang and Walsh
2006
; Overland
and Wang
2007
; Stroeve et al.
2007
; Eisenman et al.
2007
; Holland et al.
2010
; Stroeve
et al.
2012b
), the surface radiation budget (Sorteberg et al.
2007
; Bo´ et al.
2009
) and
surface temperature (Lui et al.
2008
) over the Arctic Ocean, but fewer studies of GCM
performance related to the continental part of the Arctic hydrological cycle on drainage
basin scales. Kattsov et al. (
2007
) analyzed the output of the AR4 model ensemble for four
major basins in the Pan-Arctic Drainage Region (PADB), and Roesch (
2006
) evaluated
