Article

Climate change and mountain water resources: overview and recommendations for research, management and politics

Viviroli D, D. R. Archer, Buytaert W, H. J. Fowler, G. B. Greenwood, A. F. Hamlet, Huang Y, Koboltschnig G, M. I. Litaor, J. I. López-Moreno, Lorentz S, Schädler B, Schwaiger K, Vuille M, Woods R

Hydrology and Earth System Sciences Discussions 01/2010; DOI:http://www.doaj.org/doaj?func=openurl&genre=article&issn=18122108&date=2010&volume=7&issue=3&spage=2829

Source: DOAJ

ABSTRACT Mountains are essential sources of freshwater for our world, but their role in global water resources could well be significantly altered from anticipated climate change. How well do we understand these changes today, and what are implications for water resources management and for policy? With these questions in mind, a dozen researchers – most of them with experience in collaborating with water managers – from around the world assembled for a workshop in Göschenen, Switzerland on 16–19 September 2009 by invitation of the Mountain Research Initiative (MRI). Their goal was to develop an up-to-date overview of mountain water resources and climate change and to identify pressing issues with relevance for science and society. This special issue of Hydrology and Earth System Sciences assembles contributions providing insight into climate change and water resources for selected case-study mountain regions from around the world. The present introductory article is based on analysis of these regions and on the workshop discussions. We will give a brief overview of the subject (Sect. 1), introduce the case-study regions (Sect. 2) and examine the state of knowledge regarding the importance of water supply from mountain areas for water resources in the adjacent lowlands and anticipated climate change impacts (Sect. 3). From there, we will identify research and monitoring needs (Sect. 4), make recommendations for research, water resources management and policy (Sect. 5) and finally draw conclusions (Sect. 6).

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Abstract
Mountains are essential sources of freshwater for our world, but their role in global
water resources could well be significantly altered from anticipated climate change.
How well do we understand these changes today, and what are implications for water
resources management and for policy?
With these questions in mind, a dozen researchers – most of them with experience in
collaborating with water managers – from around the world assembled for a workshop
in G¨ oschenen, Switzerland on 16–19 September 2009 by invitation of the Mountain
Research Initiative (MRI). Their goal was to develop an up-to-date overview of moun-
tain water resources and climate change and to identify pressing issues with relevance
for science and society.
This special issue of Hydrology and Earth System Sciences assembles contribu-
tions providing insight into climate change and water resources for selected case-
study mountain regions from around the world. The present introductory article is
based on analysis of these regions and on the workshop discussions. We will give
a brief overview of the subject (Sect. 1), introduce the case-study regions (Sect. 2)
and examine the state of knowledge regarding the importance of water supply from
mountain areas for water resources in the adjacent lowlands and anticipated climate
change impacts (Sect. 3). From there, we will identify research and monitoring needs
(Sect. 4), make recommendations for research, water resources management and pol-
icy (Sect. 5) and finally draw conclusions (Sect. 6).
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1 Introduction
On a global scale, mountains contribute disproportionately high runoff, provide a
favourable temporal redistribution of winter precipitation to spring and summer runoff
and reduce the variability of flows in the adjacent lowlands (Viviroli et al., 2003; Viviroli
and Weingartner, 2004). These mountain water resources are indispensable for irri-
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gation, industry and drinking water supply as well as for hydropower production both
upstream and downstream. The vital role of mountains has recently been touched
upon by several benchmark reports such as the Intergovernmental Panel on Climate
Change Fourth Assessment Report (IPCC AR4) (Solomon et al., 2007; Parry et al.,
2007) and the associated technical paper on climate change and water (Bates et al.,
2008), the Stern Review (Stern, 2007) and the Third United Nations World Water De-
velopment Report (UN WWDR3) (WWAP, 2009).
Although the IPCC AR4 projections suggest an increase in global average precipi-
tation, a decrease in precipitation and thus runoff is expected in most regions where
the relation of water supply to water demand is already critical today (Solomon et al.,
2007). This concerns especially the subtropical climate zone where both vulnerability
to water scarcity and dependence on mountain water resources are high (Viviroli et al.,
2007). Furthermore, the IPCC Technical Paper on Climate Change and Water (Bates
et al., 2008) states with high confidence that global warming will cause changes in the
seasonality of river flows where much winter precipitation currently falls as snow. This
notion is in agreement with trends already observed in mountain regions; most clearly
in the North American Cordillera (e.g. Stewart et al., 2005; Maurer et al., 2007, D´ ery
et al., 2009a, b; for a comprehensive overview see Stewart, 2009). Glacier-related
changes in runoff usually include increased runoff from enhanced ice melt, while water
yield will decrease in the long term. Such changes have recently been summarised by
Casassa et al. (2009) for the major mountain ranges of the world on basis of observa-
tions from recent decades.
The combination of shifts in seasonality and changes in total runoff are likely to have
consequences for future water availability, increasing the challenges for management
of water resources originating in mountains. Current management regimes based on
historic climate and hydrological variability will likely be inadequate, yet better methods
based on process understanding remain hampered by our limited understanding of
both projected climate change and hydrologic response.
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Coping with these anticipated changes requires effective and integrative water re-
sources management. As a prerequisite, it is necessary to determine reliably the
location, extent, dependability and quality of water resources, as well as the human
activities that affect those resources (cf. Young et al., 1994). At the same time, it is
essential that these findings be useful for water managers in order to pave the way for
their implementation in water resources management practice.
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2Introduction of case-study regions
This overview article is based on a number of case study regions that also make up the
contributions to this special issue. Although it is not possible to draw a complete picture
for all mountain regions of the world, we believe that our choice of case-studies forms a
solid basis for identifying typical problems concerning climate change and management
of water resources with focus on mountain areas.
The regions studied are listed in Table 1, and Fig. 1 indicates the location of the
regions on a world map. Also shown in Fig. 1 is the significance of mountain areas
for downstream water resources, which is quantified here by the index for Water Re-
sources Contribution (WRC) after Viviroli et al., 2007. WRC is the ratio of lowland
water availability (surplus or deficit) to water supply (only surplus is considered, see
below) from mountains and identifies the importance of a mountain raster cell for water
resources supply in the hydrologically related lowland area.
A more in-depth characterisation of the regions studied is provided in Fig. 2 on the
basis of the following metrics:
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– Water stress: Dynamic Water Stress Index (DWSI) as introduced by Wada et
al. (2010), averaged over cells of 0.5◦×0.5◦. DWSI is based on the well-known
Water Stress Index (WSI) which expresses how much of the available water is
taken up by the demand. DWSI extends WSI by considering duration, frequency
and severity of water stress over a period of 44 years (1958 to 2001). Values
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above 0.2 indicate medium water stress, and above 0.4 indicate high water stress.
The dot indicates the mean value for the entire region (including the lowland por-
tions), and the grey bars indicate the range of water stress observed in the entire
region.
– Water management capacity: capacity of the water management sector to adapt
to projected climate change. We judged 14 questions organised in four thematic
blocks: institutional capacity; political conditions; manager competence (educa-
tion, training and experience); and knowledge transfer with researchers. For each
block, a score of 1 means low capacity, and a score of 5 indicates high capacity.
The summary score is the average of the scores achieved in the four thematic
blocks. The grey bars indicate the range of scores observed in the four thematic
blocks.
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– Scientific capacity – national: scientific capacity in water resources and climate
change available in the respective nation. This is assessed through 11 ques-
tions organised in four thematic blocks: boundary conditions (e.g. funding, re-
search centres); competence in research; data availability and access; and state
of knowledge. A score of 1 means low capacity, and a score of 5 indicates high ca-
pacity. The grey bars indicate the range of capacity observed in the four thematic
blocks.
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– Scientific capacity – international: Similar to national scientific capacity, only that
here, the capacity available for the respective region at international level is as-
sessed.
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The main goal of this assessment is to illustrate the level of diversity in both likely
water stresses and the capacity to deal with water stress that occur in our case-study
regions, thus providing a framework for more detailed assessments and subsequent
recommendations. It should be borne in mind that the variation may be large even
within a single region, particularly with regard to water stress and water management
capacity.
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In part (a) of Fig. 2, the capacity of water management to adapt to climate change
is plotted against water stress for each region. In general, high physical water stress
is found together with low adaptation capacity, which is detrimental for the security
and reliability of water supply. Slight deviation from this general trend is found in the
Pyrenees (PYR) and the Drakensberg Mountains (DRM) where relatively high average
water stress is met by well-developed management capacity. It should be noted that
the value drawn for water stress refers to the mean of the entire case-study region,
which may mask smaller areas with high water stress. This applies, for example, to
Bolivia, Ecuador and Peru which were chosen to represent the Tropical Andes (ANT).
The average water stress computed for this region is 0.15, while the arid parts of the
region (the Andes themselves, including the Pacific slopes as well as the lowlands to
the west) show values well above 0.4. Similar reservations apply to the average water
stress value for the Karakoram Himalaya (0.29), especially because the Indus Plains –
where the majority of the population lives – suffer from even more severe water stress
(Archer et al., 2010), frequently with values well above 0.8. The average value for
the Pyrenees (0.22) also hides that stress is much higher in the adjacent River Ebro
Plain. It is therefore important to consider the value range indicated by the grey bars
in Fig. 2 and to bear in mind that the level of water stress is very diverse in some
regions. The top left of Fig. 2 shows the central and eastern part of the European Alps
(ALC and ALE). In these regions there is a very high level of management capacity and
generally low water stress, the latter occurring almost exclusively outside of the actual
mountainous region.
Part (b) of Fig. 2 assesses the scientific capacity to deal with climate change ques-
tions for our case-study regions. It shows that regions with low national scientific ca-
pacity can usually obtain slightly higher research capacity at the international level,
most notably in the Tropical Andes (ANT) and the Karakoram Himalaya (HIK). In prac-
tice, international scientific support will obviously require appropriate funding which will
usually also be of international origin. On the other hand, where there is high national
scientific capacity, international scientific capacity usually lags a little behind, although
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international projects (such as research funded by the EU in the case of the Euro-
pean Alps, ALC and ALE, and the Pyrenees, PYR) may still make the region attractive
for international research and lead to a relatively high level of international scientific
capacity. The Upper Changjiang region (UCJ) presents an outlier from the aforemen-
tioned connection as it has relatively high national scientific capacity but rather poor
international capacity. The emerging economic power of China has led to international
scientific aid becoming less available as the country is increasingly expected to rely on
its own scientific resources.
Part (c) of Fig. 2, finally, is a synthesis of parts (a) and (b) and compares maximum
scientific capacity available at national or international level with water management
capacity to adapt to climate change. It shows that for some regions, scientific capacity
(national or international or both) is clearly higher than water management capacity,
which points to a need for the better implementation of scientific findings into water
management practice. This is most prominent for the Pacific Northwest (PNW) but also
occurs in the East Mediterranean region (EM), the Upper Changjiang region (UCJ),
the Karakoram Himalaya (HIK), the Drakensberg Mountains (DRM) and the Pyrenees
(PYR). In the case of the Pacific Northwest (PNW), both high scientific capacity and
high water management capacity are actually present, but science is not integrated
with the management community. In spite of sophisticated infrastructure and manage-
ment systems, the capacity to deal with climate change impacts is limited as soon as it
exceeds the natural variability (see Hamlet et al., 2010). This illustrates that inflexibility
and resistance to change are even possible in highly developed and successful man-
agement systems and may become an obstacle to effective adaptation. In contrast, the
management systems that have resulted in areas of relatively high water stress may
be much better able to cope with droughts because they are already common events
(Hamlet et al., 2010).
The diversity of settings observed in our cross-section of regions calls for a region-
ally and sometimes even locally differentiated view to future management. At the same
time, the detrimental concurrence of high water stress and low management capac-
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ity seems to be a common problem that urgently calls for improvements in research,
monitoring, management and information exchange, which we will address in Sects. 4
and 5 of this article. For more subtle distinctions, several categories would need to
be separated, such as access to infrastructure, management capacity in the context of
climate variability, ability to assess future impacts and devise appropriate adaptation
strategies or capacity to implement change.
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3State of knowledge
As a basis for identifying research and monitoring needs (Sect. 4) and making recom-
mendations (Sect. 5), we first need to discuss the state of knowledge on provision of
runoff from mountains (supply), consumption of water in the lowlands (demand) and
options for balancing demand and supply. This will enable us to discuss what kind of
information is needed to answer the questions raised by water resources management
and planning and how it can be obtained and disseminated.
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3.1Water supply (runoff from mountains)
3.1.1Present state
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Viviroli et al. (2007) recently presented a comprehensive overview of the role of moun-
tains in water supply. On the basis of global runoff fields (Fekete et al., 2002), a moun-
tain typology (Meybeck et al., 2001) as well as further data on population distribution
and climate zones, they derived a set of global maps at a resolution of 0.5◦×0.5◦,
revealing that 23% of mountain areas world-wide are essential for downstream region
hydrology in the earth system context, while another 30% have a supportive role. When
the actual lowland water use is considered explicitly, 7% of the global mountain area
has an essential role in water resources, while another 37% provides important sup-
portive supply (Fig. 1). This is of special importance in arid and semiarid regions where
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the vulnerability to seasonal and regional water shortages is high. Moreover, moun-
tains in the arid zone clearly deliver a disproportionate share of total discharge (66.5%)
when compared to their share of total area (29.8%). Critically important mountain re-
gions are found in the Middle East, South Africa, parts of the Rocky Mountains and
the Andes. The importance of mountain water resources from the western part of the
Himalaya and from the Tibetan Plateau is particularly marked because these regions
partly compensate considerable lowland water deficits (Archer et al., 2010).
Snowmelt plays a major role in seasonal runoff patterns and water supply outside
of the humid tropics. This was recently shown by Barnett et al. (2005) who used the
output of a macro-scale hydrological model with a resolution of 0.5◦×0.5◦to assess
the ratio of accumulated annual snowfall to annual runoff. The authors also compared
the simulated annual runoff to the capacity of existing reservoirs, which served to iden-
tify cases where sufficient reservoir storage capacity is available to buffer seasonal
shifts in runoff caused by earlier snowmelt (see also Sect. 3.1.5). In their analysis,
Barnett et al. (2005) found that about one-sixth of the world’s population lives within
snowmelt-dominated catchments with low reservoir storage, this domain being poten-
tially vulnerable to shifts in runoff caused by climate change impacts on seasonal snow.
A critical region, for example, is the Western Himalaya where a modelling study for the
Satluj River basin (a tributary to the Indus River) by Singh and Jain (2003) suggests
that about 75% of the summer runoff is generated from snowmelt. On the neighbouring
Jhelum River basin, Archer and Fowler (2008) show a similar dependence of summer
runoff on preceding winter snowfall.
The significance of glaciers to water supply depends principally on the proportion of
catchments that they occupy (i.e. the greater the distance from glaciers, the smaller
their influence, cf. Zappa and Kan, 2007; Koboltschnig et al., 2008; Kaser et al., 2009;
Lambrecht and Mayer, 2009; Koboltschnig et al., 2010). Therefore, globally valid state-
ments about this significance are not possible. It is also often difficult to make a quan-
titative distinction between the contribution from melting of seasonal snow and from
glaciers, even though nival melt from lower elevations generally precedes the glacial
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contribution from higher elevations (Weingartner and Aschwanden, 1992). The recent
controversy on rates of melting of Himalayan glaciers (see IPCC, 2010 and Sect. 3.1.3)
is placed in perspective by preliminary results by Armstrong and Racoviteanu (2009)
who found that the annual contribution of glacier melt water to streamflow in the Nepal
Himalayas represents 2–3% of the total annual streamflow volume of the rivers of Nepal
and that seasonal contributions are not likely to exceed 2–13% of the total annual flow
volume measured at lower altitude hydrometric stations (see also Alford, 2008). For
the Indus River basin, situated in a drier climatological region, the glacial regime plays
an important role in the high-altitude catchments, but its influence decreases strongly
toward the margins of the mountains (Archer et al., 2010). In contrast, proportional
flow from glaciers over large areas in the tropical Andes is much higher because the
mitigatory influence of snow is limited (see Sect. 3.1.3).
Glaciers may provide a smoothing effect for water resources by complementing irreg-
ular runoff from highly variable summer precipitation with much more stable melt runoff
(see e.g. Hock et al., 2005). With reference to studies from the Cascade Mountains
(Fountain and Tangborn, 1985) and the Alps (Chen and Ohmura, 1990), Casassa et
al. (2009) conclude that a minimum coefficient of variation in summer runoff is reached
with a share in glaciated area of about 40%. In addition, glaciers reduce the interan-
nual variability of summer flows with their long-term buffering function (Zappa and Kan,
2007).
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3.1.2Past trends in mountain runoff
Trend analyses over the historic record are very difficult for both mountainous and
lowland areas. Results depend heavily on the methodology implemented and the time-
frame of the study (see e.g. Radziejewski and Kundzewicz, 2004), and the high vari-
ability of precipitation and temperature often lead to inconclusive findings. Particular
challenges are imposed by interannual and cyclic variations in precipitation and moun-
tain snowpacks that are caused by large-scale circulation modes such as the El Ni˜ no
– Southern Oscillation, the Eurasian Pattern, the North Atlantic Oscillation, the North
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Pacific Oscillation, the Pacific North American Pattern, the Pacific Decadal Oscillation
and the Indian Monsoon to name but a few. Some studies have removed interannual
variability due to natural climate modes from time series, allowing for more reliable
trend detection (Vuille and Milana, 2007), but the relatively short time span of most
data records (typically a few decades) remains a major impediment to the detection of
conclusive trends.
For mountain areas, trend detection is assumed to be easier due to the high climatic
sensitivity of these environments, although much depends on the particular frame of
a trend study (see also Sect. 4.1.7). For Switzerland, Birsan et al. (2005) identified
changes in streamflow since 1930, with increases in winter, spring and autumn, which
the authors attribute tentatively to a shift from snowfall to rainfall and increased and
earlier snow melt due to a rise in air temperature. These streamflow trends were found
to be positively correlated with mean basin elevation (and strongest for medium flows),
thus suggesting that mountain basins are among the most vulnerable environments in
terms of climate-induced streamflow changes. In summer, however, when most runoff
is provided on an annual basis, both decreasing and increasing trends are observed.
The heterogeneity of these trend signals is illustrated by the recent analysis by Barben
et al. (2010) for Switzerland. For the French part of the Alps, Renard et al. (2008)
detected a trend towards earlier snowmelt. For the western United States, a number
of studies found that more precipitation is falling as rain instead of snow in winter, and
that snow melt occurs earlier (e.g. Hamlet et al., 2005; Mote et al., 2005; Knowles et
al., 2006). As regards the associated changes in runoff (Dettinger et al., 1995; Cayan
et al., 2001; Regonda et al., 2005; Stewart et al., 2005), Barnett et al. (2008) were
successful in identifying an anthropogenic “fingerprint” by using a multivariable detec-
tion and attribution methodology (see also Hamlet et al., 2010). Particular difficulties
apply however to trend analyses in the mid-elevations of the semi-arid and arid climate
zones. In these critical regions, the natural runoff pattern of most of the large streams
has been altered, largely by dams or diversions (cf. D¨ oll et al., 2009), which makes it
difficult to assess changes in the natural response of amount and timing of streamflow
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(cf. Stewart, 2009).
Although changes in temperature and precipitation certainly have the biggest impact
on streamflow from a global viewpoint, it should be borne in mind that other factors can
also effect changes in streamflow in some regions. In Mediterranean mountains such
as the Pyrenees, for example, depopulation and subsequent land abandonment have
led to vegetation growth which has been the main driver for reduced runoff generation
and decreasing streamflow (Begueria et al., 2003; L´ opez-Moreno et al., 2008).
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3.1.3Climate change projections
Scenario projections for the impacts of climate change on precipitation and runoff are
subject to large uncertainties at the global scale. This is apparent from the results
of different GCMs which are not consistent everywhere in the sign of change – and
where they are, the magnitude of change is often very different (Bates et al., 2008;
Stewart, 2009; see also Buytaert et al., 2009). Climate change scenario projections
are particularly difficult for mountain areas owing to the difficulties in modelling regions
with marked topography (see Sects. 3.1.4 and 4).
Bates et al. (2008) ascertain the “very robust” finding that warming would lead to
change in the seasonality of snowmelt-dominated rivers and that snow-dominated re-
gions are particularly sensitive to changes in temperature. Depending on altitude, early
snowmelt may lead to more frequent spring flooding at the local scale, and summer irri-
gation water shortages may occur in regions that are dominated today by nival regimes.
Large changes are expected especially at low latitudes, e.g. in south-east and central
Asia (Parry et al., 2007). In regions where dependence on glacier runoff is high, shifts
in seasonality and decreases in the amount of glacial melt will cause a reduction in
water availability as well as reducing the buffering effect of glacier runoff during the dry
season (e.g. in the Tropical Andes, see Vuille et al., 2008; Coudrain et al., 2005, or
in central Asia, see Hagg and Braun, 2005). Owing to the limited research available
at present, projections regarding the future state of glaciers are however difficult and
subject to errors. This was recently shown by the controversy about the false IPCC
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statement that the Himalayan Glaciers could disappear by 2035 at present warming
rates (see Bagla, 2009; IPCC, 2010; Schiermeier, 2010; see also Sect. 3.1.1). In ad-
dition, research concerning the future state of glaciers must go beyond focusing on
surface air temperature and must also consider global shortwave radiation (Huss et al.,
2009) or, in the case of tropical glaciers, atmospheric moisture (M¨ olg et al., 2006).
Considering the present state and anticipated changes, a number of regions are
particularly vulnerable to changes in mountain runoff and subsequent deterioration of
water resources supply in the adjacent lowlands.
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– Viviroli et al. (2007) identify vulnerable regions where a high dependence on
mountain runoff in the lowlands coincides with anticipated decrease in precipi-
tation and growth in population. This applies mainly to river basins in the sub-
tropical and wet-dry tropical climate zones where the capacity to adapt to changes
is also low. Particularly vulnerable regions encompass great parts of the large Hi-
malayan river basins that are, according to recent population data (ORLN, 2002),
home to over 1.3 billion people today, but also the Middle East (e.g. Euphrates and
Tigris River basins), North, East and South Africa as well as the dry parts of the
Andes (in the central and northern Andes: the western side and the highlands; in
the southern Andes: the eastern side).
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– The UN WWDR3 (WWAP, 2009) mentions two mountain-related systems where
high vulnerability meets limited possibility of adaptation. The first are snow melt
systems such as the Indus River basin, the Ganges-Brahmaputra River basin and
Northern China. The second are the semi-arid and arid tropics with limited snow
melt and limited groundwater like parts of the Indian subcontinent, Sub-Saharan
Africa and Southern and Western Australia. The reasons for the vulnerability of
these systems vary strongly from region to region and encompass a number of
anticipated changes, such as unfavourable changes in the amount and timing of
runoff, rainfall variability, groundwater tables, population growth and food demand.
Similarly diverse are the factors that limit adaptability, such as limited capacity to
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7, 2829–2895, 2010
Climate change and
mountain water
resources
D. Viviroli et al.
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further extend the existing infrastructure, water resources that are already over-
allocated or a lack of public funds.
3.1.4Representation of mountains in climate and hydrological models
Climatological and hydrological modelling are important tools for laying the foundations
for successful and sustainable water management. Insight into important processes of
mountain areas is achieved through process-oriented hydrological modelling exercises
with focus on snow and glacier melt. A number of such studies have been conducted
for meso-scale catchments in the European Alps (e.g. Gurtz et al., 2003; Verbunt et al.,
2003; Zappa et al., 2003; Schaefli et al., 2005; Horton et al., 2006; Lehning et al., 2006;
Huss et al., 2008; Koboltschnig et al., 2008; Magnusson et al., 2010), the Scandina-
vian mountains (Hock, 1999; Hock and Holmgren, 2005), the Rocky Mountains (e.g.
Letsinger and Olyphant, 2007; Stahl et al., 2007; Comeau et al., 2009; DeBeer and
Pomeroy, 2009; see also overview by Bales et al., 2006) and the Western Himalaya
(e.g. Singh and Bengtsson, 2003; Singh and Jain, 2003; Rees and Collins, 2006; Konz
et al., 2007; Akthar et al., 2008). Global macro-scale studies (e.g. Barnett et al., 2005;
Adam et al., 2009) are equally important in providing the bigger picture.
Climatological and hydrological modelling is, however, particularly challenging in
mountain environments for two reasons. First, the pronounced spatial and temporal
heterogeneity of conditions in mountain areas calls for high model resolutions and thus
also for detailed physiographic information (e.g. soil and land use types). The latter is
usually only available for limited areas, which restricts the availability of reliable mod-
elling efforts mostly to case studies at the meso scale. Second, relevant processes in
mountain areas are not understood sufficiently. This concerns especially orographic
precipitation and snowfall, which are among the most difficult variables to simulate in
climate models, even at high spatial and temporal resolutions. Another area of un-
certainty concerns the magnitude of the feedback effects (see Sect. 4.1.6) and their
influence on the energy balance. Due to the limited process understanding, formula-
tion of such effects varies substantially between individual models. Furthermore, the
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case-study regions

climate change

climate change impacts

dozen researchers –

draw conclusions

Earth System Sciences assembles contributions

freshwater

global water resources

issues

mountain areas

Mountain Research Initiative

mountain water resources

present introductory article

special issue

up-to-date overview

water managers –

water resources

water resources management

water supply

Climate change and mountain water resources: overview and recommendations for research, management and politics

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