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Global-scale hydrological response to future glacier mass loss

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Worldwide glacier retreat and associated future runoff changes raise major concerns over the sustainability of global water resources, but global-scale assessments of glacier decline and the resulting hydrological consequences are scarce. Here we compute global glacier runoff changes for 56 large-scale glacierized drainage basins to 2100 and analyse the glacial impact on streamflow. In roughly half of the investigated basins, the modelled annual glacier runoff continues to rise until a maximum (‘peak water’) is reached, beyond which runoff steadily declines. In the remaining basins, this tipping point has already been passed. Peak water occurs later in basins with larger glaciers and higher ice-cover fractions. Typically, future glacier runoff increases in early summer but decreases in late summer. Although most of the 56 basins have less than 2% ice coverage, by 2100 one-third of them might experience runoff decreases greater than 10% due to glacier mass loss in at least one month of the melt season, with the largest reductions in central Asia and the Andes. We conclude that, even in large-scale basins with minimal ice-cover fraction, the downstream hydrological effects of continued glacier wastage can be substantial, but the magnitudes vary greatly among basins and throughout the melt season.
Contribution of future glacier runoff changes (between 2000 and 2090) to the macroscale basin runoff in all 56 investigated basins The ratio of glacier runoff change to basin runoff, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta Q{^{\prime} }_{{\rm{g}}}/{Q}_{{\rm{basin}}}$$\end{document}, is evaluated for the period July to October (January to April for the southern hemisphere, and throughout the year in the tropics). For basins with substantial glacier runoff decreases (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta Q{^{\prime} }_{{\rm{g}}}/{Q}_{{\rm{basin}}} < -$$\end{document}5%) in at least one month, the ratio refers to the month (given in brackets below the basin names) with the largest reduction in glacier runoff. Basins with negligible glacier impact (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$|\Delta Q{^{\prime}}_{{\rm{g}}}/{Q}_{{\rm{basin}}}|<$$\end{document} 5%) are shown in grey, and the remaining basins, which show glacier runoff increases that exceed 5% in at least one month, in dark blue. The results refer to multi-GCM means and RCP4.5. Small dots refer to population density \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$>$$\end{document} 100 km⁻² on a 0.5 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times$$\end{document} 0.5° grid as an indicator for potential downstream socio-environmental impacts.
Projected glacier runoff changes and contribution to basin-scale runoff The results are based on glacier runoff changes over 2000–2090 (multi-GCM mean, RCP4.5) for July to October (January to April for the southern hemisphere). For the Santa basin (inner tropics) the results refer to the months July to October as the largest glacier runoff reductions are found in the austral winter (dry season). a, Relative runoff changes from the initially glacierized area (adjusted by basin-specific water-transit times to the basin’s mouth), \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta Q{^{\prime} }_{{\rm{g}}}$$\end{document}. b, Glacier runoff changes relative to the macroscale basin runoff, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta Q{^{\prime} }_{{\rm{g}}}/{Q}_{{\rm{basin}}}$$\end{document}. Vertical lines connect the minimum and maximum changes. c, Glacierization as a function of geographic latitude. The results are shown for each continent in the order of decreasing \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta Q{^{\prime} }_{{\rm{g}}}/{Q}_{{\rm{basin}}}$$\end{document}. Only the 28 basins in which \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$| \Delta Q{^{\prime} }_{{\rm{g}}}/{Q}_{{\rm{basin}}}|$$\end{document} exceeds 5% for at least one of the four months are shown.
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1Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, Zurich, Switzerland. 2Department of Geosciences, University of Fribourg,
Fribourg, Switzerland. 3Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA. 4Department of Earth Sciences, Uppsala University,
Uppsala, Sweden. *e-mail:
Worldwide glacier retreat and associated future runoff
changes raise major concerns over the sustainability of
global water resources14, but global-scale assessments of
glacier decline and the resulting hydrological consequences
are scarce5,6. Here we compute global glacier runoff changes
for 56 large-scale glacierized drainage basins to 2100 and
analyse the glacial impact on streamflow. In roughly half of
the investigated basins, the modelled annual glacier runoff
continues to rise until a maximum (‘peak water’) is reached,
beyond which runoff steadily declines. In the remaining
basins, this tipping point has already been passed. Peak water
occurs later in basins with larger glaciers and higher ice-cover
fractions. Typically, future glacier runoff increases in early
summer but decreases in late summer. Although most of the
56 basins have less than 2% ice coverage, by 2100 one-third
of them might experience runoff decreases greater than 10%
due to glacier mass loss in at least one month of the melt sea-
son, with the largest reductions in central Asia and the Andes.
We conclude that, even in large-scale basins with minimal ice-
cover fraction, the downstream hydrological effects of contin-
ued glacier wastage can be substantial, but the magnitudes
vary greatly among basins and throughout the melt season.
Glacierized large-scale drainage basins cover 26% of the global
land surface outside Greenland and Antarctica and are populated
by almost one-third of the world’s population7. Melt waters from
glaciers contribute to and modulate downglacier streamflow, which
affects freshwater availability, hydropower operations, sediment
transport and aquatic ecosystems2,3,8. Glacier runoff typically shows
a distinct seasonality with a minimum in the snow-accumulation
season (or dry season in the tropics) and a pronounced maximum
in the melt season (or wet season) compared with ice-free basins.
Thus, glacier melt water can compensate for seasons and years of
otherwise low flow or droughts in lowland areas downstream of gla-
cierized mountain regions1,6.
Mountain glaciers around the globe have responded strongly
to recent climate change and are expected to experience continued
mass loss and retreat throughout the twenty-first century911. As gla-
ciers recede, water is released from long-term glacial storage. Thus,
annual glacier runoff volume typically increases until a maximum
is reached, often referred to as ‘peak water’12, beyond which runoff
decreases because the reduced glacier area cannot support rising
meltwater volumes anymore13. As a glacier retreats and disappears,
or reaches a new equilibrium (balanced mass budget), annual run-
off from the initially glacierized area may return to its initial value
prior to glacier retreat (Fig. 1). In contrast, runoff during the melt
season is expected to fall below the initial value, because the glacier
provides less and less melt water from long-term storage, which
impacts seasonal freshwater availability14,15.
Many studies have investigated the effects of climate change on
glacier runoff using observations or modelling, with a recent focus
on High Mountain Asia14,16,17 and the Andes1820. The degree to
which glacier runoff contributes to downglacier river runoff var-
ies greatly from basin to basin2123 and throughout the year, with
glacier contributions in individual months that reach > 25%, even
in catchments with < 1% glacierization24,25. Most studies find that
peak water has already been reached or passed19,20,26 or is expected
to occur in the coming two or three decades14,15,17,27,28. However,
it remains unclear how representative these results are globally,
as most glacio-hydrological studies have been local in scale, typi-
cally focused on highly glacierized headwaters1416,19,20,2628 or indi-
vidual regions4,23,24. Notable exceptions are the large-scale studies by
Kaser et al3. and Schaner et al.25, but they do not provide any future
projections or analyse peak water. Another study projected runoff
from all glaciers on Earth until 2100, but did not consider changes
Global-scale hydrological response to future
glacier mass loss
Matthias Huss 1,2* and Regine Hock3,4
Basin runoff (km3 yr–1)
ΔM = 0 ΔM < 0
Glacier net mass loss
Air temperature
Time (yr)
ΔM = 0
(or glacier
Melt-season runoff
Annual runoff
"Peak water"
Fig. 1 | Schematic illustration of the changes in runoff from a glacierized
basin in response to continuous atmospheric warming. The glacier is
initially in balance, that is, the annual glacier mass budget Δ M=  0, and
it is assumed that all the components of the water balance, except for
glacier-storage change, remain unaltered. The changes in melt-season
runoff illustrated here are typical of glaciers in climates with a pronounced
melt and accumulation season. See Supplementary Material for more
information on the concept of peak water.
© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
NATURE CLIMATE CHANGE | VOL 8 | FEBRUARY 2018 | 135–140 | 135
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... The increase in the negative glacier mass balance trends during the first decades of the 21 st century highlighted by several studies (e.g. Braun et al., 2019;Dussaillant et al., 2019;Seehaus et al., 2019), raises concerns about the future runoff and water availability (Radic and Hock, 2013;Huss and Hock, 2018). For the coming years, an increase in glacier melt and runoff is expected with the maximum contribution of glacier runoff to the streamflow ("peak water") to be reached in the next decades for many Andean regions Huss and Hock, 2018;IPCC, 2019;Ayala et al., 2020). ...
... Braun et al., 2019;Dussaillant et al., 2019;Seehaus et al., 2019), raises concerns about the future runoff and water availability (Radic and Hock, 2013;Huss and Hock, 2018). For the coming years, an increase in glacier melt and runoff is expected with the maximum contribution of glacier runoff to the streamflow ("peak water") to be reached in the next decades for many Andean regions Huss and Hock, 2018;IPCC, 2019;Ayala et al., 2020). However, in many glacierized areas of the Andes there is a lack of ground truth data and hence model projections still require better calibration and validation, either by long-term meteorological records or glacier mass balance measurements. ...
... Under this scenario, for many glacierized areas as their glaciers recede the glacier runoff (defined as the sum of rain, snowmelt, and ice melt) will also increase until its long-term maximum has been reached, process termed as "peak water". Figure 4-15a displays the peak water scheme presented by Huss and Hock (2018), which indicate that as glaciers adjust their size in response to climate variations (increase of temperature), long-term changes in meltwater production can be expected. Hence, this may affect the local availability of water resources. ...
Glaciers on Earth along other components of the cryosphere are important for the climate system. However, it is widely known that the vast majority of glaciers are retreating and thinning since the early part of the 20th century. Additionally, future projections have highlighted that at the end of the 21st century, glaciers are going to lose a considerable part of their remaining mass. These glacier changes have several implications for physical, biological and human systems, affecting the water availability for downstream communities and contribute to sea level rise. Unlike other regions, where glaciers are less relevant for the overall hydrology, glaciers in South America constitute a critical resource since minimum flow levels in headwaters of the Andean mountains are usually sustained by ice melt, especially during late summer and droughts, when the contribution from the seasonal snow cover is depleted. In the last decades, the number of studies has increased considerable, however, in the Southern Andes and the surrounding sub-Antarctic islands glaciers still are less studied in comparison with their counterparts in the Northern Hemisphere. The few studies on glacier mass balance in this region suggest a risk of water scarcity for many Andean cities which freshwater supply depends on glacial meltwater. Additionally, glaciers on sub-Antarctic islands have not been completely assessed and their contribution to the sea level rise has been roughly estimated. Hence, the monitoring of glaciers is critical to provide baseline information for regional climate change adaptation policies and facilitate potential hazard assessments. Close and long-range remote sensing techniques offer the potential for repeated measurements of glacier variables (e.g. glacier mass balance, area changes). In the last decades, the number of sensors and methods has increased considerably, allowing time series analysis as well as new and more precise measurements of glacier changes. The main goal of this thesis is to investigate and provide a detailed quantification of glacier elevation and mass changes of the Southern Andes with strong focus on the Central Andes of Chile and South Georgia. Six comprehensive studies were performed to provide a better understanding of the development and current status of glaciers in this region. Overall, the glacier changes were estimated by means of various remote sensing techniques. For the Andes as a whole, the first continent-wide glacier elevation and mass balance was conducted for 85% of the total glacierized area of South America. A detailed estimation of mass changes using the bi-static synthetic aperture radar interferometry (Shuttle Radar Topography Mission -SRTM- and TerraSAR-X add-on for Digital Elevation Measurements -TanDEM-X- DEMs) over the years 2000 to 2011/2015 was computed. A total mass loss rate of 19.43 ± 0.60 Gt a-1 (0.054 ± 0.002 mm a-1 sea level rise contribution) from elevation changes above ground, sea or lake level was calculated, with an extra 3.06 ± 1.24 Gt a-1 derived from subaqueous ice mass loss. The results indicated that about 83% of the total mass loss observed in this study was contributed by the Patagonian icefields (Northern and Southern), which can largely be explained by the dynamic adjustments of large glaciers. For the Central Andes of Chile, four studies were conducted where detailed times series of glacier area, mass and runoff changes were performed on individual glaciers and at a region level (Maipo River basin). Glaciers in the central Andes of Chile are a fundamental natural resources since they provide freshwater for ecosystems and for the densely populated Metropolitan Region of Chile. The first study was conducted in the Maipo River basin to obtain time series of basin-wide glacier mass balance estimates. The estimations were obtained using historical topographic maps, SRTM, TanDEM-X, and airborne Light Detection and Ranging (LiDAR) digital elevation models. The results showed spatially heterogeneous glacier elevation and mass changes between 1955 and 2000, with more negative values between 2000 and 2013. A mean basin-wide glacier mass balance of −0.12 ± 0.06 m w.e. a-1 , with a total mass loss of 2.43 ± 0.26 Gt between 1955–2013 was calculated. For this region, a 20% reduction in glacier ice volume since 1955 was observed with associated consequences for the meltwater contribution to the local river system. Individual glacier studies were performed for the Echaurren Norte and El Morado glaciers. Echaurren Norte Glacier is a reference glacier for the World Glacier Monitoring Service. An ensemble of different data sets was used to derive a complete time series of elevation, mass and area changes. For El Morado Glacier, a continuous thinning and retreat since the 20th century was found. Overall, highly negative elevation and mass changes rates were observed from 2010 onwards. This coincides with the severe drought in Chile in this period. Moreover, the evolution of a proglacial lake was traced. If drained, the water volume poses an important risk to down-valley infrastructure. The glacier mass balance for the Central Andes of Chile has been observed to be highly correlated with precipitation (ENSO). All these changes have provoked a glacier volume reduction of one-fifth between 1955 and 2016 and decrease in the glacier runoff contribution in the Maipo basin. The thesis closes with the first island-wide glacier elevation and mass change study for South Georgia glaciers, one of the largest sub-Antarctic islands. There, glaciers changes were inferred by bi-static synthetic aperture radar interferometry between 2000 and 2013. Frontal area changes were mapped between 2003 and 2016 to roughly estimate the subaqueous mass loss. Special focus was given to Szielasko Glacier where repeated GNSS measurements were available from 2012 and 2017. The results showed an average glacier mass balance of −1.04 ± 0.09 m w.e. a-1 and a mass loss rate of 2.28 ± 0.19 Gt a-1 (equivalent to 0.006 ± 0.001 mm a-1 sea level rise) in the period 2000-2013. An extra 0.77 ± 0.04 Gt a-1 was estimated for subaqueous mass loss. The concurrent area change rate of the marine and lake-terminating glaciers amounts to −6.58 ± 0.33 km2 a-1 (2003–2016). Overall, the highest thinning and retreat rates were observed for the large outlet glaciers located at the north-east coast. Neumayer Glacier showed the highest thinning rates with the disintegration of some tributaries. Our comparison between InSAR data and GNSS measurements showed good agreement, demonstrating consistency in the glacier elevation change rates from two different methods. Our glacier elevation and mass changes assessment provides a baseline for further comparison and calibration of model projection in a sparsely investigated region. Future field measurements, long-term climate reanalysis, and glacier system modelling including ice-dynamic changes are required to understand and identify the key forcing factors of the glacier retreat and thinning.
... H igh Mountain Asia (HMA), the Earth's most important and vulnerable water tower 1,2 , is warming at a rate that is double the global average (0.32 °C per decade compared with the global average of 0.16 °C per decade (refs. 3,4 )) and is characterized by a rapidly changing cryosphere 5,6 and related changes in the hydrological and sedimentary regimes of mountain rivers [7][8][9] . The projected declining meltwater supply from HMA's glaciers and snow packs in the near future (for example, slightly before or after 2050) coupled with population growth will probably exacerbate water stress and social instability in the region [10][11][12] . ...
... Future research in the region must target less-studied landscape responses to climate change 91 , including paraglacial adjustments, slope instability, hazard cascades and glacial/permafrost erosion and related sediment yields rather than focusing solely on cryosphere reduction and changes to freshwater supply 1,2,7,8,[10][11][12]15 . Recently, glacier status and glacial lakes in HMA have been mapped [34][35][36][79][80][81][108][109][110] , and knowledge regarding glacial lake evolution in relation to glacier changes has improved 79,111 . ...
Global warming-induced melting and thawing of the cryosphere are severely altering the volume and timing of water supplied from High Mountain Asia, adversely affecting downstream food and energy systems that are relied on by billions of people. The construction of more reservoirs designed to regulate streamflow and produce hydropower is a critical part of strategies for adapting to these changes. However, these projects are vulnerable to a complex set of interacting processes that are destabilizing landscapes throughout the region. Ranging in severity and the pace of change, these processes include glacial retreat and detachments, permafrost thaw and associated landslides, rock–ice avalanches, debris flows and outburst floods from glacial lakes and landslide-dammed lakes. The result is large amounts of sediment being mobilized that can fill up reservoirs, cause dam failure and degrade power turbines. Here we recommend forward-looking design and maintenance measures and sustainable sediment management solutions that can help transition towards climate change-resilient dams and reservoirs in High Mountain Asia, in large part based on improved monitoring and prediction of compound and cascading hazards.
... Estimating snowmelt and glacier-melt streamflow is vital for effective planning and management of surface water in the UIB. The changes in glaciers under the influence of climate change will strongly impact river flow and hydrological regimes in the UIB (Huss and Hock, 2018). However, the precise estimation of streamflow in a basin characterized by mountains covered with permanent snow and glacier is considered an unsolved problem, which deserves the attention of hydrology community (Lettenmaier et al. 2015). ...
... However, the in-situ gauges/stations are sparsely distributed, especially in developing countries like Pakistan , particularly across the complex topographic and diverse climatic regions of UIB. There are several factors associated with the relatively poor performance of different hydrological models in the glacial regions; including the unavailability of enough in-situ observations for calibration and validation of hydrological models (Rahman et al. 2020a), complex topography, the seasonal impact of snow, and glaciers on streamflow and river discharge (Tuo et al. 2018), and climate change (Huss and Hock, 2018;Lettenmaier et al. 2015). ...
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This study appraised and compared the performance of process-based hydrological SWAT (soil and water assessment tool) with a machine learning-based multi-layer perceptron (MLP) models for simulating streamflow in the Upper Indus Basin. The study period ranges from 1998 to 2013, where SWAT and MLP models were calibrated/trained and validated/tested for multiple sites during 1998–2005 and 2006–2013, respectively. The performance of both models was evaluated using nash–sutcliffe efficiency (NSE), coefficient of determination (R2), Percent BIAS (PBIAS), and mean absolute percentage error (MAPE). Results illustrated the relatively poor performance of the SWAT model as compared with the MLP model. NSE, PBIAS, R2, and MAPE for SWAT (MLP) models during calibration ranged from the minimum of 0.81 (0.90), 3.49 (0.02), 0.80 (0.25) and 7.61 (0.01) to the maximum of 0.86 (0.99), 9.84 (0.12), 0.87 (0.99), and 15.71 (0.267), respectively. The poor performance of SWAT compared with MLP might be influenced by several factors, including the selection of sensitive parameters, selection of snow specific sensitive parameters that might not represent actual snow conditions, potential limitations of the SCS-CN method used to simulate streamflow, and lack of SWAT ability to capture the hydropeaking in Indus River sub-basins (at Shatial bridge and Bisham Qila). Based on the robust performance of the MLP model, the current study recommends to develop and assess machine learning models and merging the SWAT model with machine learning models.
... The timing of the delta system's formation was very likely related to the phase of intensive deglaciation between 3000-9000 BP [29]. The greatest sediment transport period occurred during "peak water" when meltwater production was highest [30]. After this point, runoff has steadily declined and so has the transport capacity of glacier-fed rivers. ...
... This, together with relatively intense glacial isostatic uplift after deglaciation, also promoted the progradation of delta systems. A similar trend of delta progradation in recent conditions was observed by Bendixen et al. [32] in western Greenland, where the glaciers are generally much larger and are still on the rising limb of "peak water" [30]. ...
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Glacier-fed hydrological systems in high latitude regions experience high seasonal variation in meltwater runoff. The peak in runoff usually coincides with the highest air temperatures which drive meltwater production. This process is often accompanied by the release of sediments from within the glacier system that are transported and suspended in high concentrations as they reach the proglacial realm. Sediment-laden meltwater is later transported to the marine environment and is expressed on the surface of fjords and coastal waters as sediment plumes. Direct monitoring of these processes requires complex and time-intensive fieldwork, meaning studies of these processes are rare. This paper demonstrates the seasonal dynamics of the Trebrevatnet lake complex and evolution of suspended sediment in the lake and sediment plumes in the adjacent Ekmanfjorden. We use the Normalized Difference Suspended Sediment Index (NDSSI) derived from multi-temporalSentinel-2 images for the period between 2016–2021. We propose a new SSL index combining the areal extent of the sediment plume with the NDSSI for quantification of the sediment influx to the marine environment. The largest observed sediment plume was recorded on 30 July 2018 and extended to more than 40 km2 and a SSL index of 10.4. We identified the greatest sediment concentrations in the lake in the beginning of August, whereas the highest activity of the sediment plumes is concentrated at the end of July. The temporal pattern of these processes stays relatively stable throughout all ablation seasons studied. Sediment plumes observed with the use of optical satellite remote sensing data may be used as a proxy for meltwater runoff from the glacier-fed Trebrevatnet system. We have shown that remote-sensing-derived suspended sediment indexes can (after proper in situ calibration)serve for large scale quantification of sediment flux to fjord and coastal environments.
... Studies on the Indus Basin treat the basin or its upper part as a whole (e.g., Akhtar et al., 2008;Lutz et al., 2016;Wijngaard et al., 2017), many comparing the Indus with other river basins (e.g., Kaser et al., 2010;Savoskul and Smakhtin, 2013;Lutz et al., 2014;Huss and Hock, 2018). Exploring the cryospheric contribution to river flow though physically-based models has been largely limited to studies on individual subbasins or glaciers. ...
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Pakistan is the most glaciated country on the planet but faces increasing water scarcity due to the vulnerability of its primary water source, the Indus River, to changes in climate and demand. Glacier melt constitutes over one-third of the Indus River’s discharge, but the impacts of glacier shrinkage from anthropogenic climate change are not equal across all eleven subbasins of the Upper Indus. We present an exploration of glacier melt contribution to Indus River flow at the subbasin scale using a distributed surface energy and mass balance model run 2001–2013 and calibrated with geodetic mass balance data. We find that the northern subbasins, the three in the Karakoram Range, contribute more glacier meltwater than the other basins combined. While glacier melt discharge tends to be large where there are more glaciers, our modeling study reveals that glacier melt does not scale directly with glaciated area. The largest volume of glacier melt comes from the Gilgit/Hunza subbasin, whose glaciers are at lower elevations than the other Karakoram subbasins. Regional application of the model allows an assessment of the dominant drivers of melt and their spatial distributions. Melt energy in the Nubra/Shyok and neighboring Zaskar subbasins is dominated by radiative fluxes, while turbulent fluxes dominate the melt signal in the west and south. This study provides a theoretical exploration of the spatial patterns to glacier melt in the Upper Indus Basin, a critical foundation for understanding when glaciers melt, information that can inform projections of water supply and scarcity in Pakistan.
... Glacier mass balance evolution in Central Asia is a key variable to determining the impact of climate change on water availability [1][2][3][4][5]. Glaciers store water and act as water towers; this water can be used for irrigation and hydropower [6][7][8]. Tien Shan glaciers, as with most mountain glaciers globally, currently present a negative mass balance [9][10][11]. Recent studies on glacier mass balance reconstruction in Tien Shan and Pamir suggest an overall continuous mass loss for the past two decades [10][11][12][13][14][15][16][17]. ...
Mass balance measurements for Golubin glacier in Northern Tien Shan, Kyrgyzstan, have been discontinuous over the last century, with significant data gaps. We provide a unique over 100-year-long mass balance series on daily resolution. We applied a temperature index model calibrated with glaciological measurements and validated with secular mass balances derived from independent length change observations. A comparison with other recent geodetic studies reveals good agreement. Golubin lost −0.16 ± 0.45 m w.e. a−1 from 1900/1901 to 2020/2021. From the long-term mass balance time series, we identify a shift to a more negative/less positive regime with time, with a steepening of the ablation and accumulation gradients, especially for the past two decades. We observe a parallel shift of the mass balance gradient accompanied by a rotation of the ablation gradient due to increased ablation at the glacier tongue and accumulation above the equilibrium line altitude. This tendency is believed to intensify in the future, affecting glaciers’ mass balance sensitivity to changes in atmospheric conditions and year-to-year variability and resulting in irregular melt water release feeding the rivers that provide water to Bishkek. These kinds of datasets are sparse for Tien Shan and, yet, indispensable to enhancing our understanding of glacier changes in High Mountain Asia.
... Since the previous few decades, the cryospheric regime has undergone dramatic changes, which are mostly related to rising temperatures (Liu and Chen, 2000;Radi et al, 2013;Shea et al., 2015;Bolch et al., 2019). Huss and Hock (2018) analyzed global scale hydrological response to glacier mass loss in 56 large-scale glacierized river basins until 2100 using Global Glacier Evolution Model (GloGEM). GloGEM was used to estimate glacial runoff for each glacierized basin by incorporating all important glaciological processes such as mass accumulation and ablation, as well as variations in glacier extent and surface elevation. ...
... The changing connection between glaciology and hydrology with warming will further contribute to divergent hydrological responses between the endorheic and exorheic basins of the AWT. Under the RCP4.5 scenario, annual glacier run-off in all glacier-fed rivers of the AWT (except the Indus River 118 ) is projected to reach a maximum in the middle of this century and to decline thereafter 118,135 . However, these changes can also influence run-off in endorheic rivers, such as the Amu Darya River, which is highly dependent upon glacier melt 136,137 . ...
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The Hindu Kush–Karakoram–Himalayan system, named the Third Pole because it is the largest global store of frozen water after the polar regions, provides a reliable water supply to almost 2 billion people. Marked atmospheric warming has changed the balance of this so-called Asian water tower and altered water resources in downstream countries. In this Review, we synthesize observational evidence and model projections that describe an imbalance in the Asian water tower caused by accelerated transformation of ice and snow into liquid water. This phase change is associated with a south–north disparity due to the spatio-temporal interaction between the westerlies and the Indian monsoon. A corresponding spatial imbalance is exhibited by alterations in freshwater resources in endorheic or exorheic basins. Global warming is expected to amplify this imbalance, alleviating water scarcity in the Yellow and Yangtze River basins and increasing scarcity in the Indus and Amu Darya River basins. However, the future of the Asian water tower remains highly uncertain. Accurate predictions of future water supply require the establishment of comprehensive monitoring stations in data-scarce regions and the development of advanced coupled atmosphere–cryosphere–hydrology models. Such models are needed to inform the development of actionable policies for sustainable water resource management. Atmospheric warming has imbalanced the Hindu Kush–Karakoram–Himalayan system (the Asian water tower (AWT)). Yao et al. review observed changes in atmospheric water and freshwater AWT constituents, focusing on their future consequences for freshwater resources and vulnerable societies across downstream basins. During 1980–2018, warming of the Asian Water Tower (AWT) was 0.42 °C per decade, twice the global average rate.Annual precipitation in the AWT increased by 11 mm per decade in endorheic basins and 12 mm per decade in exorheic basins, despite decreased precipitation in some large river basins.From 2000 to 2018, total glacier mass in the AWT decreased by about 340 Gt whereas total water mass in lakes increased by 166 Gt.Changes in the westerlies and the Indian monsoon led the AWT to develop an imbalance characterized by water gains in endorheic basins and water losses in exorheic basins.Ubiquitous increases in precipitation and river run-off are projected in the future of the AWT; however, these changes cannot meet the accelerating water demands of downstream regions and countries.Comprehensive monitoring systems, advanced modelling capacity and sustainable water management are needed to develop adaptation policies for the AWT through collaboration between upstream and downstream regions and countries. During 1980–2018, warming of the Asian Water Tower (AWT) was 0.42 °C per decade, twice the global average rate. Annual precipitation in the AWT increased by 11 mm per decade in endorheic basins and 12 mm per decade in exorheic basins, despite decreased precipitation in some large river basins. From 2000 to 2018, total glacier mass in the AWT decreased by about 340 Gt whereas total water mass in lakes increased by 166 Gt. Changes in the westerlies and the Indian monsoon led the AWT to develop an imbalance characterized by water gains in endorheic basins and water losses in exorheic basins. Ubiquitous increases in precipitation and river run-off are projected in the future of the AWT; however, these changes cannot meet the accelerating water demands of downstream regions and countries. Comprehensive monitoring systems, advanced modelling capacity and sustainable water management are needed to develop adaptation policies for the AWT through collaboration between upstream and downstream regions and countries.
The simulation and prediction of glacially derived runoff are significant for water resource management and sustainable development in water-stressed arid regions. However, the application of a hydrological model in such regions is typically limited by the intricate runoff production mechanism, which is associated with snow and ice melting, and sparse monitoring data over glacierized headwaters. To address these limitations, this study develops a set of mathematical models with a certain physical significance and an efficient particle swarm optimization algorithm by applying long- and short-term memory networks on the glacierized Muzati River basin. First, the trends in the runoff, precipitation, and air temperature are analyzed from 1990 to 2015, and differences in their correlations in this period are exposed. Then, Particle Swarm Optimization–Long Short-Term Memory (PSO-LSTM) and Bi-directional Long Short-Term Memory (BiLSTM) models are combined and applied to the precipitation and air temperature data to predict the glacially derived runoff. The prediction accuracy is validated by the observed runoff at the river outlet at the Pochengzi hydrological station. Finally, two other types of models, the RF (Random Forest) and LSTM (Long Short-Term Memory) models, are constructed to verify the prediction results. The results indicate that the glacially derived runoff is strongly correlated with air temperature and precipitation. However, in the study region over the past 26 years, the air temperature was not obviously increasing, and the precipitation and glacially derived runoff were significantly decreasing. The test results show that the PSO-LSTM and BiLSTM runoff prediction models perform better than the RF and LSTM models in the glacierized Muzati River basin. In the validation period, among all models, the PSO-LSTM model has the smallest mean absolute error and root-mean-square error and the largest coefficient of determination of 6.082, 8.034, and 0.973, respectively. It is followed by the BiLSTM model having a mean absolute error, root-mean-square error, and coefficient of determination of 6.751, 9.083, and 0.972, respectively. These results imply that both the particle swarm optimization algorithm and the bi-directional structure can effectively enhance the prediction accuracy of the baseline LSTM model. The results presented in this study can provide a deeper understanding and a more appropriate method of predicting the glacially derived runoff in glacier-fed river basins.
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Understanding the effects of snowmelt in terms of large slope deformation in high mountainous areas could come from the use of Interferometric Synthetic Aperture Radar (InSAR) techniques. In this work, we investigate a slow moving, extremely large landslide (~20 km2) in the Chitral region in Northern Pakistan, which threatens several villages. Our InSAR analyses, using Sentinel-1 data which span a period of six years, allowed us to retrieve the spatio-temporal pattern of downslope deformation for both ascending and descending orbits. The results highlight a worrying situation where the crown of the landslide is moving relatively fast (from 36 to 80 mm/yr). Several sackung-type of movements and other signs of instability were observed in many locations over the crown. As for the toe of the large landslide, a western sliding sector offers a different mechanism than its eastern counterpart where the deformation appears to accumulate through time. This brief description has two implications. One from the most practical perspective, as it calls for further studies and attention from local administrations. And, it also scientifically highlights the strength of InSAR when it comes to unveiling slow deformation regimes, which may be invisible through the eye of other techniques, although they may still lead to catastrophic failures. Such considerations can be even framed beyond the scale explored in this manuscript. In ither words, the same mechanism and threat to local communities can be present across the whole Hindukush-Himalayan-Karakoram range, where the water release may not just come through snowmelt but it is the result of glacier receding due to climate change.
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Knowledge of the ice thickness distribution of glaciers and ice caps is an important prerequisite for many glaciological and hydrological investigations. A wealth of approaches has recently been presented for inferring ice thickness from characteristics of the surface. With the Ice Thickness Models Intercomparison eXperiment (ITMIX) we performed the first coordinated assessment quantifying individual model performance. A set of 17 different models showed that individual ice thickness estimates can differ considerably – locally by a spread comparable to the observed thickness. Averaging the results of multiple models, however, significantly improved the results: on average over the 21 considered test cases, comparison against direct ice thickness measurements revealed deviations on the order of 10 ± 24 % of the mean ice thickness (1σ estimate). Models relying on multiple data sets – such as surface ice velocity fields, surface mass balance, or rates of ice thickness change – showed high sensitivity to input data quality. Together with the requirement of being able to handle large regions in an automated fashion, the capacity of better accounting for uncertainties in the input data will be a key for an improved next generation of ice thickness estimation approaches.
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Glacierized mountains are often referred to as our world's water towers because glaciers both store water over time and regulate seasonal stream flow, releasing runoff during dry seasons when societies most need water. Ice loss thus has the potential to affect human societies in diverse ways, including irrigation, agriculture, hydropower, potable water, livelihoods, recreation, spirituality, and demography. Unfortunately, research focusing on the human impacts of glacier runoff variability in mountain regions remains limited, and studies often rely on assumptions rather than concrete evidence about the effects of shrinking glaciers on mountain hydrology and societies. This article provides a systematic review of international research on human impacts of glacier meltwater variability in mountain ranges worldwide, including the Andes, Alps, greater Himalayan region, Cascades, and Alaska. It identifies four main areas of existing research: (1) socioeconomic impacts; (2) hydropower; (3) agriculture, irrigation, and food security; and (4) cultural impacts. The article also suggests paths forward for social sciences, humanities, and natural sciences research that could more accurately detect and attribute glacier runoff and human impacts, grapple with complex and intersecting spatial and temporal scales, and implement transdisciplinary research approaches to study glacier runoff. The objective is ultimately to redefine and reorient the glacier-water problem around human societies rather than simply around ice and climate. By systematically evaluating human impacts in different mountain regions, the article strives to stimulate cross-regional thinking and inspire new studies on glaciers, hydrology, risk, adaptation, and human–environment interactions in mountain regions.
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Global warming is expected to significantly affect the runoff regime of mountainous catchments. Simple methods for calculating future glacier change in hydrological models are required in order to reliably assess economic impacts of changes in the water cycle over the next decades. Models for temporal and spatial glacier evolution need to describe the climate forcing acting on the glacier, and ice flow dynamics. Flow models, however, demand considerable computational resources and field data input and are moreover not applicable on the regional scale. Here, we propose a simple parameterization for calculating the change in glacier surface elevation and area, which is mass conserving and suited for hydrological modelling. The Δ h -parameterization is an empirical glacier-specific function derived from observations in the past that can easily be applied to large samples of glaciers. We compare the Δ h -parameterization to results of a 3-D finite-element ice flow model. As case studies, the evolution of two Alpine glaciers of different size over the period 2008–2100 is investigated using regional climate scenarios. The parameterization closely reproduces the distributed ice thickness change, as well as glacier area and length predicted by the ice flow model. This indicates that for the purpose of transient runoff forecasts, future glacier geometry change can be approximated using a simple parameterization instead of complex ice flow modelling. Furthermore, we analyse alpine glacier response to 21st century climate change and consequent shifts in the runoff regime of a highly glacierized catchment using the proposed methods.
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Water availability on the continents is important for human health, economic activity, ecosystem function and geophysical processes. Because the saturation vapour pressure of water in air is highly sensitive to temperature, perturbations in the global water cycle are expected to accompany climate warming. Regional patterns of warming-induced changes in surface hydroclimate are complex and less certain than those in temperature, however, with both regional increases and decreases expected in precipitation and runoff. Here we show that an ensemble of 12 climate models exhibits qualitative and statistically significant skill in simulating observed regional patterns of twentieth-century multidecadal changes in streamflow. These models project 10-40% increases in runoff in eastern equatorial Africa, the La Plata basin and high-latitude North America and Eurasia, and 10-30% decreases in runoff in southern Africa, southern Europe, the Middle East and mid-latitude western North America by the year 2050. Such changes in sustainable water availability would have considerable regional-scale consequences for economies as well as ecosystems.
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Mountain ranges are the world's natural water towers and provide water resources for millions of people. However, their hydrological balance and possible future changes in river flow remain poorly understood because of high meteorological variability, physical inaccessibility, and the complex interplay between climate, cryosphere, and hydrological processes. Here, we use a state-of-the art glacio-hydrological model informed by data from high-altitude observations and the latest climate change scenarios to quantify the climate change impact on water resources of two contrasting catchments vulnerable to changes in the cryosphere. The two study catchments are located in the Central Andes of Chile and in the Nepalese Himalaya in close vicinity of densely populated areas. Although both sites reveal a strong decrease in glacier area, they show a remarkably different hydrological response to projected climate change. In the Juncal catchment in Chile, runoff is likely to sharply decrease in the future and the runoff seasonality is sensitive to projected climatic changes. In the Langtang catchment in Nepal, future water availability is on the rise for decades to come with limited shifts between seasons. Owing to the high spatiotemporal resolution of the simulations and process complexity included in the modeling, the response times and the mechanisms underlying the variations in glacier area and river flow can be well constrained. The projections indicate that climate change adaptation in Central Chile should focus on dealing with a reduction in water availability, whereas in Nepal preparedness for flood extremes should be the policy priority.
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In the Tarim River Basin, water resources from the mountain areas play a key role due to the extremely arid climate of the lowlands. This study presents an analysis of future climate change impacts on glaciers and surface water availability for headwater catchments of the Aksu River, the most important tributary to the Tarim River. We applied a glacio-hydrological model that underwent a comprehensive multivariable and multiobjective model calibration and evaluation, based on daily and interannual discharge variations and glacier mass changes. Transient glacier geometry changes are simulated using the Δh-approach. For the ensemble-based projections, we considered three different emission scenarios, nine global climate models (GCMs) and two regional climate models, and different hydrological model parameters derived from the multiobjective calibration. The results show a decline in glacier area of −90% to −32% until 2099 (reference ~2008) (based on the 5–95 percentile range of the ensemble). Glacier melt is anticipated to further increase or stay at a high level during the first decades of the 21st century, but then declines because of decreased glacier extents. Overall discharge in the Aksu headwaters is expected to be increased in the period 2010–2039 (reference 1971–2000), but decreased in 2070–2099. Seasonally, projections show an increase in discharge in spring and early summer throughout the 21st century. Discharge changes in mid to late summer are more variable, with increases or decreases depending on the considered period and GCM. Uncertainties are largely caused by differences between the different GCMs, with further important contributions from different emission scenarios in the second half of the 21st century. Contributions from the hydrological model parameters to the ensemble uncertainty were generally found to be small.
The high mountains of Asia—encompassing the Himalayas, the Hindu Kush, Karakoram, Pamir Alai, Kunlun Shan, and Tian Shan mountains—have the highest concentration of glaciers globally, and 800 million people depend in part on meltwater from them. Water stress makes this region vulnerable economically and socially to drought, but glaciers are a uniquely drought-resilient source of water. Here I show that these glaciers provide summer meltwater to rivers and aquifers that is sufficient for the basic needs of 136 million people, or most of the annual municipal and industrial needs of Pakistan, Tajikistan, Turkmenistan, Uzbekistan and Kyrgyzstan. During drought summers, meltwater dominates water inputs to the upper Indus and Aral river basins. Uncertainties in mountain precipitation are poorly known, but, given the magnitude of this water supply, predicted glacier loss would add considerably to drought-related water stress. Such additional water stress increases the risk of social instability, conflict and sudden, uncontrolled population migrations triggered by water scarcity, which is already associated with the large and rapidly growing populations and hydro-economies of these basins.
In glacier-fed rivers, melting of glacier ice sustains streamflow during the driest times of the year, especially during drought years. Anthropogenic and ecologic systems that rely on this glacial buffering of low flows are vulnerable to glacier recession as temperatures rise. We demonstrate the evolution of glacier melt contribution in watershed hydrology over the course of a 184-year period from 1916 to 2099 through the application of a coupled hydrological and glacier dynamics model to the Hood River basin in Northwest Oregon, USA. We performed continuous simulations of glaciological processes (mass accumulation and ablation, lateral flow of ice and heat conduction through supra-glacial debris), which are directly linked with seasonal snow dynamics as well as other key hydrologic processes (e.g. evapotranspiration and subsurface flow). Our simulations show that historically, the contribution of glacier melt to basin water supply was up to 79% at upland water management locations. We also show that supraglacial debris cover on the Hood River glaciers modulates the rate of glacier recession and progression of dry season flow at upland stream locations with debris-covered glaciers. Our model results indicate that dry season (July to September) discharge sourced from glacier melt started to decline early in the 21st century following glacier recession that started early in the 20th century. Changes in climate over the course of the current century will lead to 14-63% (18-78%) reductions in dry season discharge across the basin for IPCC emission pathway RCP4.5 (RCP8.5). The largest losses will be at upland drainage locations of water diversions that were dominated historically by glacier melt and seasonal snowmelt. The contribution of glacier melt varies greatly not only in space but also in time. It displays a strong decadal scale fluctuations that are super-imposed on the effects of a long-term climatic warming trend. This decadal variability results in reversals in trends in glacier melt, which underscore the importance of long-time series of glacio-hydrologic analyses for evaluating the hydrological response to glacier recession.
This paper demonstrates the potential of combining observed river discharge information with climate-driven water balance model (WBM) outputs to develop composite runoff fields. Such combined runoff fields simultaneously reflect the numerical accuracy of the discharge measurements and preserve the spatial and temporal distribution of simulated runoff. Selected gauging stations from the World Meteorological Organization Global Runoff Data Centre (GRDC) data archive were geographically coregistered to a gridded simulated topological network at 30′ (longitude × latitude) spatial resolution (STN-30p). Interstation regions between gauging stations along the STN-30p network were identified, and annual interstation runoff was calculated. The annual interstation runoff was compared with outputs from WBM calculations, which were performed using long-term mean monthly climate forcings (air temperature and precipitation). The simulated runoff for each cell was multiplied by the ratio of observed to simulated runoff of the corresponding interstation region from the GRDC data set to create spatially distributed runoff fields at 30′ resolution. The resulting composite runoff fields (UNH/GRDC Composite Runoff Fields V1.0) are released to the scientific community along with intermediate data sets, such as station attributes and long-term monthly regimes of the selected gauging stations, the simulated topological network (STN-30p), STN-30p derived attributes for the selected stations, and gridded fields of the interstation regions along STN-30p. These data sets represent high-resolution fields that are of value to a broad range of water-related research, including terrestrial modeling, climate-atmosphere interactions, and global water resource assessments.