Geoscience Reference
In-Depth Information
scales. Meier (
1984
) was the first to recognize that these glaciers outside the two vast ice
sheets in Antarctic and Greenland—though only comprising \ 1 % of the Earth's total ice
volume—are major contributors to global sea-level rise due to worldwide glacier wastage
in response to global warming. Various studies have attempted to quantify the mass losses
of these ice bodies and their effect on rising sea level indicating that glaciers outside the ice
sheets have contributed between one-third and one-half of global sea-level rise during the
last decades (Dyurgerov and Meier
2005
; Kaser et al.
2006
; Cogley
2009a
,
b
; Gardner et al.
2013
). The glacier contribution to future sea-level rise is expected to remain significant as
the global temperature is expected to further increase (Lemke et al.
2007
).
On regional and local scales, glaciers are significant contributors to seasonal riverflow,
serving as frozen reservoirs of water that supplement runoff during warm and dry periods
of low riverflow. The ongoing glacier retreat has important implications for downstream
river flows, regional water supplies, sustainability of aquatic ecosystems, and hydropower
generation (e.g., Kaser et al.
2010
; Huss
2011
; Immerzeel et al.
2010
). Glacier runoff is
intrinsically linked to the glacier's mass balance, the latter defined as the sum of its total
accumulation (mostly due to snowfall, windblown snow, avalanches, and condensation)
and ablation (mostly due to melt, calving of icebergs, wind erosion, evaporation, subli-
mation) over a stated period of time (Cogley et al.
2011
). Note that mass loss is defined
negatively. Despite the importance of glaciers as modifiers of global and regional water
cycles, there are relatively few attempts to assess recent and project future glacier mass
changes and quantity their impacts on riverflow on global and regional scales.
Previous review-type publications have focused either on glacier mass changes and their
measurement (Braithwaite
2002
; Cogley
2011
) or on glacier runoff and its characteristics
(Jansson et al.
2003
; Hock et al.
2005
; Hock and Jansson
2005
) generally focusing on local
catchment or glacier scales. In contrast, here we combine both themes to highlight the links
between glaciers and river runoff focusing exclusively on regional and global scales. Our
goal is to provide a critical overview of studies that have attempted to quantify recent and
future glacier mass changes and to assess the importance of these mass changes in
streamflow on larger scales. We only consider glaciers distinct from the two ice sheets in
Greenland and Antarctica. First, we will provide an overview on global glacier mass
balances including assessment techniques (Sect.
2
) and modeling of recent and future
changes (Sect.
3
). Then, we will discuss the characteristics and definition of glacier runoff
(Sect.
4
) followed by a discussion of studies exploring the role of glaciers in regional and
global hydrology (Sect.
5
).
2 Assessing glacier mass balance on regional and global scales
Simulating glacier runoff requires accurate modeling of the components of the glacier mass
balance which in turn requires mass-balance measurements for calibration and validation
of mass-balance models (Konz and Seibert
2010
). Below, we will briefly introduce the
techniques for assessing glacier mass balance on global scales before reviewing the results
of assessments and projections.
2.1 Assessments by in situ mass-balance measurements
Until recently, all global assessments of the mass balance of glaciers relied on some form
of extrapolation of available glacier-wide mass-balance measurements. The most tradi-
tional of these techniques, the so-called glaciological method, is based on snow probings
