Editing IPCC:AR6/SROCC/Chapter-2 (section)

== Box 2.3 Local Responses to Water Shortage in northwest India ==

<div id="section-2-3-1-3key-impacts-and-vulnerability-block-1"></div>

Agriculture in Ladakh, a cold arid mountain region (~100,000 km 2 ) in the western Himalaya of India with median elevation of 3,350 m a.s.l. and mean annual precipitation of less than 100 mm, is highly dependent on streams for irrigation in the agricultural season in the spring and summer (Nüsser et al., 2012 <sup>[[#fn:r389|389]]</sup> ; Barrett and Bosak, 2018 <sup>[[#fn:r390|390]]</sup> ). Glaciers in Ladakh, largely located at 5,000 – 6,000 m a.s.l. and small in size have retreated at least since the late 1960s although less pronounced than in many other Himalayan regions (Chudley et al., 2017 <sup>[[#fn:r391|391]]</sup> ; Schmidt and Nüsser, 2017 <sup>[[#fn:r392|392]]</sup> ). However, the effect of glaciers on streamflow in Ladakh is poorly constrained, and measurements on changes in runoff and snow cover are lacking (Nüsser et al., 2018 <sup>[[#fn:r394|394]]</sup> ).

To cope with seasonal water scarcity at critical times for irrigation, villagers in the region have developed four types of artificial ice reservoirs: basins, cascades, diversions and a form known locally as ice stupas. All these types of ice reservoirs capture water in the autumn and winter, allowing it to freeze, and hold it until spring, when it melts and flows down to fields (Clouse et al., 2017 <sup>[[#fn:r394|394]]</sup> ; Nüsser et al., 2018 <sup>[[#fn:r395|395]]</sup> ). In this way, they retain a previously unused portion of the annual flow and facilitate its use to supplement the decreased flow in the following spring (Vince, 2009 <sup>[[#fn:r396|396]]</sup> ; Shaheen, 2016 <sup>[[#fn:r397|397]]</sup> ). Frozen basins are formed from water which is conveyed across a slope through channels and check dams to shaded surface depressions near the villages. Cascades and diversions direct water to pass over stone walls, slowing its movement and allowing it to freeze. Ice stupas direct water through pipes into fountains, where it freezes into conical shapes (Box 2.3 Figure 1). These techniques use local materials and draw on local knowledge (Nüsser and Baghel, 2016 <sup>[[#fn:r398|398]]</sup> ).

A study examined 14 ice reservoirs, including ice stupas, and concluded that they serve as ‘site-specific water conservation strategies; and that they can be regarded as appropriate local technologies to reduce seasonal water scarcity at critical times (Nüsser et al., 2018 <sup>[[#fn:r399|399]]</sup> ). It listed the benefits of ice reservoirs as improved water availability in spring, reduction of seasonal water scarcity and resulting crop failure risks, and the possibility of growing cash crops. However, the study questioned their usefulness as a long-term adaptation strategy, because their operation depends on winter runoff and freeze-thaw cycles, both of which are sensitive to interannual variability, and often deviate from the optimum range required for effective functioning of the reservoirs. It also raised questions about the financial costs and labour requirements, which vary across the four types of ice reservoirs.

<div id="section-2-3-1-3key-impacts-and-vulnerability-block-2"></div>

<span id="box-2.3-figure-1"></span>
<!-- START IMG -->
<!-- IMG TITLE -->
'''Box 2.3, Figure 1'''

<span id="box-2.3-figure-1-ice-stupas-in-ladakh-india-photo-padma-rigzin"></span>
<!-- IMG CAPTION -->
'''Box 2.3, Figure 1 Ice stupas in Ladakh, India (Photo: Padma Rigzin)'''
<!-- IMG FILE -->
[[File:e42ad17bfae42aba8464d847f9707e30 IPCC-SROCC-CB_2_3_one_column_wide-3000x1750.jpg]]

Box 2.3, Figure 1 Ice stupas in Ladakh, India (Photo: Padma Rigzin)

<!-- END IMG -->
<div id="section-2-3-1-3key-impacts-and-vulnerability-block-4">
</div>

<span id="drinking-water-supply"></span>
===== 2.3.1.3.3 Drinking water supply =====

Only a few studies provide detailed empirical assessments of the effects of cryosphere change on the amounts of drinking water supply. Decreases in drinking water supplies due to reduced glacier and snowmelt water have been reported for rural areas in the Nepal Himalaya (McDowell et al., 2013 <sup>[[#fn:r400|400]]</sup> ; Dangi et al., 2018 <sup>[[#fn:r401|401]]</sup> ), but the tropical Andes have received the most attention, including both urban conglomerates and some rural areas, where water resources are especially vulnerable to climate change due to water scarcity and increased demands (Chevallier et al., 2011 <sup>[[#fn:r402|402]]</sup> ; Somers et al., 2018 <sup>[[#fn:r403|403]]</sup> ), amidst rapidly retreating glaciers (Burns and Nolin, 2014 <sup>[[#fn:r404|404]]</sup> ).

The contribution of glacier water to the water supply of La Paz, Bolivia, between 1963–2006 was assessed at 15% annually and 27% during the dry season (Soruco et al., 2015 <sup>[[#fn:r405|405]]</sup> ), though rising as high as 86% during extreme drought months (Buytaert and De Bièvre, 2012 <sup>[[#fn:r406|406]]</sup> ). Despite a 50% area loss, the glacier retreat has not contributed to reduced water supplies for the city, because increased melt rates have compensated for reductions in glacier volume. However, for a complete disappearance of the glaciers, assuming no change in precipitation, a reduction in annual runoff by 12% and 24% in the dry season was projected (Soruco et al., 2015 <sup>[[#fn:r407|407]]</sup> ) similar to reductions projected by 2050 under a RCP8.5 scenario for a basin in southern Peru (Drenkhan et al., 2019 <sup>[[#fn:r408|408]]</sup> ). Huaraz and Huancayo in Peru are other cities with high average contribution of melt water to surface water resources (up to ~20%; Buytaert et al., 2017 <sup>[[#fn:r409|409]]</sup> ) and rapid glacier retreat in their headwaters (Rabatel et al., 2013 <sup>[[#fn:r410|410]]</sup> ).

Overall, risks to water security and related vulnerabilities are highly heterogeneous varying even at small spatial scales with populations closer to the glaciers being more vulnerable, especially during dry months and droughts (Buytaert et al., 2017 <sup>[[#fn:r411|411]]</sup> ; Mark et al., 2017 <sup>[[#fn:r412|412]]</sup> ). A regional-scale modelling study including all of Bolivia, Ecuador and Peru (Buytaert et al., 2017 <sup>[[#fn:r413|413]]</sup> ) estimated that roughly 390,000 domestic water users, mostly in Peru, rely on a high (&gt;25%) long-term average contribution from glacier melt, with this number rising to almost 4 million in the driest month of a drought year. Despite ''high confidence'' in declining longer-term melt water contributions from glaciers in the tropical Andes (Figure CB6.1), major uncertainties remain how these will affect future human water use. Regional-scale water balance simulations forced by multi-model climate projections (Buytaert and De Bièvre, 2012 <sup>[[#fn:r414|414]]</sup> ), suggest a relatively limited effect of glacier retreat on water supply in four major cities (Bogota, La Paz, Lima, Quito) due to the dominance of human factors influencing water supply (Carey et al., 2014 <sup>[[#fn:r415|415]]</sup> ; Mark et al., 2017 <sup>[[#fn:r416|416]]</sup> ; Vuille et al., 2018 <sup>[[#fn:r417|417]]</sup> ), though uncertainties are large. Population growth and limited funding for infrastructure maintenance exacerbate water scarcity, though water managers have established programs in Quito and in Huancayo and the Santa and Vilcanota basins (Peru) to improve water management through innovations in grey infrastructure and ecosystem-based adaptations (Buytaert and De Bièvre, 2012 <sup>[[#fn:r418|418]]</sup> ; Buytaert et al., 2017 <sup>[[#fn:r419|419]]</sup> ; Somers et al., 2018 <sup>[[#fn:r420|420]]</sup> ).

In summary, there is ''limited evidence'' ( ''medium agreement'' ) that glacier decline places increased risks to drinking water supply. In the Andes, future increases in water demand due to population growth and other socioeconomic stressors are expected to outpace the impact of climate change induced changes on water availability regardless the emission scenario.

<div id="section-2-3-1-4water-governance-and-response-measures"></div>

<span id="water-governance-and-response-measures"></span>
==== 2.3.1.4 Water Governance and Response Measures ====

<div id="section-2-3-1-4water-governance-and-response-measures-block-1"></div>

Cryospheric changes induced by climate change, and their effects on hydrological regime and water availability, bear relevance for the management and governance of water as a resource for communities and ecosystems (Hill, 2013 <sup>[[#fn:r421|421]]</sup> ; Beniston and Stoffel, 2014 <sup>[[#fn:r422|422]]</sup> ; Carey et al., 2017 <sup>[[#fn:r423|423]]</sup> ), particularly in areas where snow and ice contribute significantly to river runoff ( ''medium confidence'' ) (Section 2.3.1.1). However, water availability is one aspect relevant for water management and governance, given that multiple and diverse decision making contexts and governance approaches and strategies can influence how the water resource is accessed and distributed ( ''medium confidence'' ) (De Stefano et al., 2010; Beniston and Stoffel, 2014 <sup>[[#fn:r424|424]]</sup> ).

A key risk factor that influences how water is managed and governed, rests on existing and unresolved conflicts that may or may not necessarily arise exclusively from demands over shared water resources, raising tensions within and across borders in river basins influenced by snow and glacier melt (Valdés-Pineda et al., 2014 <sup>[[#fn:r425|425]]</sup> ; Bocchiola et al., 2017 <sup>[[#fn:r426|426]]</sup> ). For example, in Central Asia, competing demand for water for hydropower and irrigation between upstream and downstream countries has raised tensions (Bernauer and Siegfried, 2012 <sup>[[#fn:r427|427]]</sup> ; Bocchiola et al., 2017 <sup>[[#fn:r428|428]]</sup> ). Similarly, competing demand for water is also reported in Chile (Valdés-Pineda et al., 2014 <sup>[[#fn:r429|429]]</sup> ) and in Peru (Vuille, 2013 <sup>[[#fn:r430|430]]</sup> ; Drenkhan et al., 2015 <sup>[[#fn:r431|431]]</sup> ). Since AR5, some studies have examined the impacts and risks related to projections of cryosphere-related changes in streamflow in transboundary basins in the 21 st century, and suggest that these changes create barriers in effectively managing water in some settings ( ''medium confidence'' ) ''.'' For instance, within the transnational Indus River basin, climate change impacts may reduce streamflow by the end of this century, thus putting pressure on established water sharing arrangements between nations (Jamir, 2016 <sup>[[#fn:r432|432]]</sup> ) and subnational administrative units (Yang et al., 2014b <sup>[[#fn:r433|433]]</sup> ). In this basin, management efforts may be hampered by current legal and regulatory frameworks for evaluating new dams, which do not take into account changes in streamflow that may result from climate change (Raman, 2018 <sup>[[#fn:r434|434]]</sup> ). Within the transnational Syr Darya and Amu Darya basins in Central Asia, competition for water between multiple uses, exacerbated by reductions in flow later in this century, may hamper future coordination (Reyer et al., 2017 <sup>[[#fn:r435|435]]</sup> ; Yu et al., 2019 <sup>[[#fn:r436|436]]</sup> ). However, other evidence from Central Asia suggests that relative water scarcity may not be the only factor to exacerbate conflict in this region (Hummel, 2017 <sup>[[#fn:r437|437]]</sup> ). Overall, there is ''medium confidence'' in the ability to meet future water demands in some mountain regions, given the combined uncertainties associated with accurate projections of water supply in terms of availability and the diverse sociocultural and political contexts in which decisions on water access and distribution are taken.

Since AR5, several studies highlight that integrated water management approaches, focused on the multipurpose use of water that includes water released from the cryosphere, which are important as adaptation measures, particularly for sectors reliant on this water source to sustain energy production, agriculture, ecosystems and drinking water supply (Figure 2.9). These measures, backed by effective governance arrangements to support them, demonstrate an ability to address increasing challenges to water availability arising from climate change in the mountain cryosphere, providing co-benefits through the optimisation of storage and the release of water from high mountain reservoirs ( ''medium confidence'' ). Studies in Switzerland (e.g., Haeberli et al., 2016; Brunner et al., 2019 <sup>[[#fn:r438|438]]</sup> ), Peru (e.g., Barriga Delgado et al., 2018; Drenkhan et al., 2019 <sup>[[#fn:r439|439]]</sup> ), Central Asia (Jalilov et al., 2018 <sup>[[#fn:r440|440]]</sup> ) and Himalaya (Molden et al., 2014 <sup>[[#fn:r441|441]]</sup> ; Biemans et al., 2019 <sup>[[#fn:r442|442]]</sup> ) highlight the potential of water reservoirs in high mountains, including new reservoirs located in former glacier beds, alleviating seasonal water scarcity for multiple water usages. However, concerns are also raised in the environmental literature about their actual and potential negative impacts on local ecosystems and biodiversity hotspots, such as wetlands and peat bogs, which have been reported for small high mountain reservoirs, for example, in the European Alps (Evette et al., 2011 <sup>[[#fn:r443|443]]</sup> ) and for large dam construction projects in High Mountain Asia (e.g., Dharmadhikary, 2008).

Transboundary cooperation at regional scales are reported to further support efforts that address the potential risks to water resources in terms of its availability and its access and distribution governance (Dinar et al., 2016 <sup>[[#fn:r444|444]]</sup> ). Furthermore, the UN 2030 Agenda and its Sustainable Development Goals (SDGs) (UN, 2015) may offer additional prospects to strengthen water governance under a changing cryosphere, given that monitoring and reporting on key water-related targets and indicators, and their interaction across other SDGs, direct attention to the provision of water as a key condition for development (Section 2.4). However, there is ''limited evidence'' to date to assess their effectiveness on an evidentiary basis.

<span id="landslide-avalanche-and-flood-hazards"></span>
=== 2.3.2 Landslide, Avalanche and Flood Hazards ===

<div id="section-2-3-2landslide-avalanche-and-flood-hazards-block-1"></div>

High mountains are particularly prone to hazards related to snow, ice and permafrost as these elements exert key controls on mountain slope stability (Haeberli and Whiteman, 2015 <sup>[[#fn:r445|445]]</sup> ). This section assesses knowledge gained since previous IPCC reports, in particular SREX (e.g., Seneviratne et al., 2012), and AR5 Working Group II (Cramer et al., 2014 <sup>[[#fn:r446|446]]</sup> ). In this section, observed and projected changes in hazards are covered first, followed by exposure, vulnerability and resulting impacts and risks, and finally disaster risk reduction and adaptation. Cryospheric hazards that constitute tipping points are also listed in Table 6.1 in Chapter 6.

Hazards assessed in this section range from localised effects on mountain slopes and adjacent valley floors (distance reach of up to several kilometres) to events reaching far into major valleys and even surrounding lowlands (reach of tens to hundreds of kilometres), and include cascading events. Changes in the cryosphere due to climate change influence the frequency and magnitude of hazards, the processes involved, and the locations exposed to the hazards (Figure 2.7). Natural hazards and associated disasters are sporadic by nature, and vulnerability and exposure exhibit strong geographic variations. Assessments of change are based not only on direct evidence, but also on laboratory experiments, theoretical considerations and calculations, and numerical modelling.

<div id="section-2-3-2-1observed-and-projected-changes"></div>

<span id="observed-and-projected-changes"></span>
==== 2.3.2.1 Observed and Projected Changes ====

<div id="section-2-3-2-1observed-and-projected-changes-block-1"></div>

<span id="unstable-slopes-landslides-and-glacier-instabilities"></span>
===== 2.3.2.1.1 Unstable slopes, landslides and glacier instabilities =====

Permafrost degradation and thaw as well as increased water flow into frozen slopes can increase the rate of movement of frozen debris bodies and lower their surface due to loss of ground ice (subsidence). Such processes affected engineered structures such as buildings, hazard protection structures, roads, or rail lines in all high mountains during recent decades (Section 2.3.4). Movement of frozen slopes and ground subsidence/heave are strongly related to ground temperature, ice content, and water input (Wirz et al., 2016 <sup>[[#fn:r447|447]]</sup> ; Kenner et al., 2017 <sup>[[#fn:r448|448]]</sup> ). Where massive ground ice gets exposed, retrogressive thaw erosion develops (Niu et al., 2012 <sup>[[#fn:r449|449]]</sup> ). The creep of rock glaciers (frozen debris tongues that slowly deform under gravity) is in principle expected to accelerate in response to rising ground temperatures, until substantial volumetric ice contents have melted out (Kääb et al., 2007 <sup>[[#fn:r450|450]]</sup> ; Arenson et al., 2015a <sup>[[#fn:r451|451]]</sup> ). As documented for instance for sites in the European Alps and Scandinavia for recent years to decades, rock glaciers replenished debris flow starting zones at their fronts, so that the intensified material supply associated with accelerated movement (Section 2.2.4) contributed to increased debris flow activity (higher frequency, larger magnitudes) or slope destabilisation (Stoffel and Graf, 2015 <sup>[[#fn:r452|452]]</sup> ; Wirz et al., 2016 <sup>[[#fn:r453|453]]</sup> ; Kummert et al., 2017 <sup>[[#fn:r454|454]]</sup> ; Eriksen et al., 2018 <sup>[[#fn:r455|455]]</sup> ).

There is ''high confidence'' that the frequency of rocks detaching and falling from steep slopes (rock fall) has increased within zones of degrading permafrost over the past half-century, for instance in high mountains in North America, New Zealand, and Europe (Allen et al., 2011 <sup>[[#fn:r456|456]]</sup> ; Ravanel and Deline, 2011 <sup>[[#fn:r457|457]]</sup> ; Fischer et al., 2012 <sup>[[#fn:r458|458]]</sup> ; Coe et al., 2017 <sup>[[#fn:r459|459]]</sup> ). Compared to the SREX and AR5 reports, the confidence in this finding increased. Available field evidence agrees with theoretical considerations and calculations that permafrost thaw increases the likelihood of rock fall (and also rock avalanches, which have larger volumes compared to rock falls) (Gruber and Haeberli, 2007 <sup>[[#fn:r460|460]]</sup> ; Krautblatter et al., 2013 <sup>[[#fn:r461|461]]</sup> ). These conclusions are also supported by observed ice in the detachment zone of previous events in North America, Iceland and Europe (Geertsema et al., 2006 <sup>[[#fn:r462|462]]</sup> ; Phillips et al., 2017 <sup>[[#fn:r463|463]]</sup> ; Sæmundsson et al., 2018 <sup>[[#fn:r464|464]]</sup> ). Summer heat waves have in recent years triggered rock instability with delays of only a few days or weeks in the European Alps (Allen and Huggel, 2013 <sup>[[#fn:r465|465]]</sup> ; Ravanel et al., 2017 <sup>[[#fn:r466|466]]</sup> ). This is in line with theoretical considerations about fast thaw of ice filled frozen fractures in bedrock (Hasler et al., 2011 <sup>[[#fn:r467|467]]</sup> ) and other climate impacts on rock stability, such as from large temperature variations (Luethi et al., 2015 <sup>[[#fn:r468|468]]</sup> ). Similarly, permafrost thaw increased the frequency and volumes of landslides from frozen sediments in many mountain regions in recent decades (Wei et al., 2006 <sup>[[#fn:r469|469]]</sup> ; Ravanel et al., 2010 <sup>[[#fn:r470|470]]</sup> ; Lacelle et al., 2015 <sup>[[#fn:r471|471]]</sup> ). At lower elevations in the French Alps, though, climate driven changes such as a reduction in number of freezing days are projected to lead to a reduction in debris flows (Jomelli et al., 2009 <sup>[[#fn:r472|472]]</sup> ).

A range of slope instability types was found to be connected to glacier retreat (Allen et al., 2011 <sup>[[#fn:r473|473]]</sup> ; Evans and Delaney, 2015 <sup>[[#fn:r474|474]]</sup> ). Debris left behind by retreating glaciers (moraines) slid or collapsed, or formed fast flowing water-debris mixtures (debris flows) in recent decades, for instance in the European and New Zealand Alps (Zimmermann and Haeberli, 1992 <sup>[[#fn:r475|475]]</sup> ; Blair, 1994 <sup>[[#fn:r476|476]]</sup> ; Curry et al., 2006 <sup>[[#fn:r477|477]]</sup> ; Eichel et al., 2018 <sup>[[#fn:r478|478]]</sup> ). Over decades to millennia, or even longer, rock slopes adjacent to or formerly covered glaciers, became unstable and in some cases, eventually collapsed. Related landslide activity increased in recently deglacierised zones in most high mountains (Korup et al., 2012 <sup>[[#fn:r479|479]]</sup> ; McColl, 2012 <sup>[[#fn:r480|480]]</sup> ; Deline et al., 2015 <sup>[[#fn:r481|481]]</sup> ; Kos et al., 2016 <sup>[[#fn:r482|482]]</sup> ; Serrano et al., 2018 <sup>[[#fn:r483|483]]</sup> ). For example, according to Cloutier et al. (2017) <sup>[[#fn:r484|484]]</sup> more than two-thirds of the large landslides that occurred in Northern British Columbia between 1973–2003, occurred on cirque walls that have been exposed after glacier retreat from the mid-19th century on. Ice-rich permafrost environments following glacial retreat enhanced slope mass movements (Oliva and Ruiz-Fernández, 2015 <sup>[[#fn:r485|485]]</sup> ). At lower elevations, re-vegetation and rise of tree limit are able to stabilise shallow slope instabilities (Curry et al., 2006 <sup>[[#fn:r486|486]]</sup> ). Overall, there is ''high confidence'' that glacier retreat in general has in most high mountains destabilised adjacent debris and rock slopes over time scales from years to millennia, but robust statistics about current trends in this development are lacking. This finding reconfirms, and for some processes increases confidence in related findings from the SREX and AR5 reports.

Ice break-off and subsequent ice avalanches are natural processes at steep glacier fronts. How climate driven changes in geometry and thermal regime of such glaciers influenced ice avalanche hazards over years to decades depended strongly on local conditions, as shown for the European Alps (Fischer et al., 2013 <sup>[[#fn:r487|487]]</sup> ; Faillettaz et al., 2015 <sup>[[#fn:r488|488]]</sup> ). The few available observations are insufficient to detect trends. Where steep glaciers are frozen to bedrock, there is, however, ''medium evidence'' and ''high agreement'' from observations in the European Alps and from numerical simulations that failures of large parts of these glaciers were and will be facilitated in the future due to an increase in basal ice temperature (Fischer et al., 2013 <sup>[[#fn:r489|489]]</sup> ; Faillettaz et al., 2015 <sup>[[#fn:r490|490]]</sup> ; Gilbert et al., 2015 <sup>[[#fn:r491|491]]</sup> ) .

In some regions, glacier surges constitute a recurring hazard, due to widespread, quasi-periodic and substantial increases in glacier speed over a period of a few months to years, often accompanied by glacier advance (Harrison et al., 2015 <sup>[[#fn:r492|492]]</sup> ; Sevestre and Benn, 2015 <sup>[[#fn:r493|493]]</sup> ). In a number of cases, mostly in North America and High Mountain Asia (Bevington and Copland, 2014 <sup>[[#fn:r494|494]]</sup> ; Round et al., 2017 <sup>[[#fn:r495|495]]</sup> ; Steiner et al., 2018 <sup>[[#fn:r496|496]]</sup> ), surge-related glacier advances dammed rivers, causing major floods. In rare cases, glacier surges directly inundated agricultural land and damaged infrastructure (Shangguan et al., 2016 <sup>[[#fn:r497|497]]</sup> ). Sevestre and Benn (2015) <sup>[[#fn:r498|498]]</sup> suggest that surging operates within a climatic envelope of temperature and precipitation conditions, and that shifts in these conditions can modify surge frequencies and magnitudes. Some glaciers have reduced or stopped surge activity, or are projected to do so within decades, as a consequence of negative glacier mass balances (Eisen et al., 2001 <sup>[[#fn:r499|499]]</sup> ; Kienholz et al., 2017 <sup>[[#fn:r500|500]]</sup> ). For such cases, related hazards can also be expected to decrease. In contrast, intensive or increased surge activity (Hewitt, 2007 <sup>[[#fn:r501|501]]</sup> ; Gardelle et al., 2012 <sup>[[#fn:r502|502]]</sup> ; Yasuda and Furuya, 2015 <sup>[[#fn:r503|503]]</sup> ) occurred in a region on and around the Western Tibetan plateau which exhibited balanced or even positive glacier mass budgets in recent decades (Brun et al., 2017 <sup>[[#fn:r504|504]]</sup> ). Enhanced melt water production was suggested to be able to trigger or enhance surge-type instability, in particular for glaciers that contain ice both at the melting point and considerably below (Dunse et al., 2015 <sup>[[#fn:r505|505]]</sup> ; Yasuda and Furuya, 2015 <sup>[[#fn:r506|506]]</sup> ; Nuth et al., 2019 <sup>[[#fn:r507|507]]</sup> ).

A rare type of glacier instability with large volumes (in the order of 10-100 million m 3 ) and high mobility (up to 200–300 km/h) results from the complete collapse of large sections of low-angle valley glaciers and subsequent combined ice/rock/debris avalanches. The largest of such glacier collapses have been reported in the Caucasus Mountains in 2002 (Kolka Glacier, ~130 fatalities) (Huggel et al., 2005 <sup>[[#fn:r508|508]]</sup> ; Evans et al., 2009 <sup>[[#fn:r509|509]]</sup> ), and in the Aru Range in Tibet in 2016 (twin glacier collapses with 9 fatalities) (Kääb et al., 2018 <sup>[[#fn:r510|510]]</sup> ). Although there is no evidence that climate change has played a direct role in the 2002 event, changes in glacier mass balance, water input into the glaciers, and the frozen regime of the glacier beds were involved in the 2016 collapses and at least partly linked with climate change (Gilbert et al., 2018 <sup>[[#fn:r511|511]]</sup> ). Besides the 2016 Tibet cases, it is unknown if such massive and rare collapse-like glacier instabilities can be attributed to climate change.

<div id="section-2-3-2-1observed-and-projected-changes-block-2"></div>

<span id="snow-avalanches"></span>
===== 2.3.2.1.2 Snow avalanches =====

Snow avalanches can occur either spontaneously due to meteorological factors such as loading by snowfall or liquid water infiltration following, for example, surface melt or rain-on-snow, or can be triggered by the passage of people in avalanche terrain, the impact of falling ice or rocks, or by explosives used for avalanche control (Schweizer et al., 2003 <sup>[[#fn:r512|512]]</sup> ). There is no published evidence found that addresses the links between climate change and accidental avalanches triggered by recreationists or workers. Changes in snow cover characteristics are expected to induce changes in spontaneous avalanche activity including changes in friction and flow regime (Naaim et al., 2013 <sup>[[#fn:r513|513]]</sup> ; Steinkogler et al., 2014 <sup>[[#fn:r514|514]]</sup> ).

Ballesteros-Cánovas et al. (2018) <sup>[[#fn:r515|515]]</sup> reported increased avalanche activity in some slopes of the Western Indian Himalaya over the past decades related to increased frequency of wet-snow conditions. In the European Alps, avalanche numbers and runout distance have decreased where snow depth decreased and air temperature increased (Teich et al., 2012 <sup>[[#fn:r516|516]]</sup> ; Eckert et al., 2013 <sup>[[#fn:r517|517]]</sup> ). In the European Alps and Tatras mountains, over past decades, there has been a decrease in avalanche mass and run-out distance and a decrease in avalanches with a powder part; avalanche numbers decreased below 2,000 m a.s.l., and increased above (Eckert et al., 2013 <sup>[[#fn:r518|518]]</sup> ; Lavigne et al., 2015 <sup>[[#fn:r519|519]]</sup> ; Gadek et al., 2017 <sup>[[#fn:r520|520]]</sup> ). A positive trend in the proportion of avalanches involving wet snow in December through February was shown for the last decades (Pielmeier et al., 2013 <sup>[[#fn:r521|521]]</sup> ; Naaim et al., 2016 <sup>[[#fn:r522|522]]</sup> ). Land use and land cover changes also contributed to changes in avalanches (García-Hernández et al., 2017 <sup>[[#fn:r523|523]]</sup> ; Giacona et al., 2018 <sup>[[#fn:r524|524]]</sup> ). Correlations between avalanche activity and the El Niño-Southern Oscillation (ENSO) were identified from 1950–2011 in North and South America but there was no significant temporal trend reported for avalanche activity (McClung, 2013 <sup>[[#fn:r525|525]]</sup> ). Mostly inconclusive results were reported by Sinickas et al. (2015) <sup>[[#fn:r526|526]]</sup> and Bellaire et al. (2016) <sup>[[#fn:r527|527]]</sup> regarding the relationship between avalanche activity, climate change and disaster risk reduction activities in North America. In summary, in particular in Europe, there is ''medium confidence'' in an increase in avalanche activity involving wet snow, and a decrease in the size and run-out distance of snow avalanches over the past decades.

Future projections mostly indicate an overall decrease in snow depth and snow cover duration at lower elevation (Section 2.2.2), but the probability of occurrence of occasionally large snow precipitation events is projected to remain possible throughout most of the 21st century (Section 2.2.1). Castebrunet et al. (2014) <sup>[[#fn:r528|528]]</sup> estimated an overall 20 and 30% decrease of natural avalanche activity in the French Alps for the mid and end of the 21st century, respectively, under A1B scenario, compared to the reference period 1960–1990. Katsuyama et al. (2017) <sup>[[#fn:r529|529]]</sup> reached similar conclusions for Northern Japan, and Lazar and Williams (2008) <sup>[[#fn:r530|530]]</sup> for North America. Avalanches involving wet snow are projected to occur more frequently during the winter at all elevations due to surface melt or rain-on-snow (e.g., Castebrunet et al., 2014, for the French Alps), and the overall number and runout distance of snow avalanches is projected to decrease in regions and elevations experiencing significant reduction in snow cover (Mock et al., 2017 <sup>[[#fn:r531|531]]</sup> ). In summary, there is ''medium evidence'' and ''high agreement'' that observed changes in avalanches in mountain regions will be exacerbated in the future, with generally a decrease in hazard at lower elevation, and mixed changes at higher elevation (increase in avalanches involving wet snow, no clear direction of trend for overall avalanche activity).

<div id="section-2-3-2-1observed-and-projected-changes-block-3"></div>

<span id="figure-2.7"></span>
<!-- START IMG -->
<!-- IMG TITLE -->
'''Figure 2.7'''

<span id="figure-2.7-anticipated-changes-in-high-mountain-hazards-under-climate-change-driven-by-changes-in-snow-cover-glaciers-and-permafrost-overlay-changes-in-the-exposure-and-vulnerability-of-individuals-communities-and-mountain-infrastructure."></span>
<!-- IMG CAPTION -->
'''Figure 2.7 | Anticipated changes in high mountain hazards under climate change, driven by changes in snow cover, glaciers and permafrost, overlay changes in the exposure and vulnerability of individuals, communities, and mountain infrastructure.'''
<!-- IMG FILE -->
[[File:209432aa6405ea2c6e267b9e97b74276 IPCC-SROCC-CH_2_7.jpg]]

Figure 2.7 | Anticipated changes in high mountain hazards under climate change, driven by changes in snow cover, glaciers and permafrost, overlay changes in the exposure and vulnerability of individuals, communities, and mountain infrastructure.

<!-- END IMG -->
<div id="section-2-3-2-1observed-and-projected-changes-block-4">
</div>

<span id="floods"></span>
===== 2.3.2.1.3 Floods =====

Glacier-related floods, including floods from lake outbursts (GLOFs), are documented for most glacierised mountain ranges and are among the most far-reaching glacier hazards. Past events affected areas tens to hundreds of kilometres downstream (Carrivick and Tweed, 2016 <sup>[[#fn:r532|532]]</sup> ). Retreating glaciers produced lakes at their fronts in many high mountain regions in recent decades (Frey et al., 2010 <sup>[[#fn:r533|533]]</sup> ; Gardelle et al., 2011 <sup>[[#fn:r534|534]]</sup> ; Loriaux and Casassa, 2013 <sup>[[#fn:r535|535]]</sup> ). Lake systems in High Mountain Asia also often developed on the surface of downwasting, low-slope glaciers where they coalesced from temporally variable supraglacial lakes (Benn et al., 2012 <sup>[[#fn:r536|536]]</sup> ; Narama et al., 2017 <sup>[[#fn:r537|537]]</sup> ). Corroborating SREX and AR5 findings, there is ''high confidence'' that current global glacier shrinkage caused new lakes to form and existing lakes to grow in most regions, for instance in South America, High mountain Asia and Europe (Loriaux and Casassa, 2013 <sup>[[#fn:r538|538]]</sup> ; Paul and Mölg, 2014 <sup>[[#fn:r539|539]]</sup> ; Zhang et al., 2015 <sup>[[#fn:r540|540]]</sup> ; Buckel et al., 2018 <sup>[[#fn:r541|541]]</sup> ). Exceptions occurred and are expected to occur in the future for few lakes where evaporation, runoff and reduced melt water influx in total led to a negative water balance (Sun et al., 2018a <sup>[[#fn:r542|542]]</sup> ). Also, advancing glaciers temporarily dammed rivers, lake sections, or fjords (Stearns et al., 2015 <sup>[[#fn:r543|543]]</sup> ), for instance through surging (Round et al., 2017 <sup>[[#fn:r544|544]]</sup> ), causing particularly large floods once the ice dams breached. Outbursts from water bodies in and under glaciers are able to cause floods similar to those from surface lakes but little is known about the processes involved and any trends under climate change. In some cases, the glacier thermal regime played a role so that climate driven changes in thermal regime are expected to alter the hazard potential, depending on local conditions (Gilbert et al., 2012 <sup>[[#fn:r545|545]]</sup> ). Another source of large water bodies under glaciers and subsequent floods has been subglacial volcanic activity (Section 2.3.2.1.4). There is also ''high confidence'' that the number and area of glacier lakes will continue to increase in most regions in the coming decades, and new lakes will develop closer to steep and potentially unstable mountain walls where lake outbursts can be more easily triggered by the impact of landslides (Frey et al., 2010 <sup>[[#fn:r546|546]]</sup> ; ICIMOD, 2011 <sup>[[#fn:r547|547]]</sup> ; Allen et al., 2016a <sup>[[#fn:r548|548]]</sup> ; Linsbauer et al., 2016 <sup>[[#fn:r549|549]]</sup> ; Colonia et al., 2017 <sup>[[#fn:r550|550]]</sup> ; Haeberli et al., 2017 <sup>[[#fn:r551|551]]</sup> ).

In contrast to the number and size of glacier lakes, trends in the number of glacier-related floods are not well known for recent decades (Carrivick and Tweed, 2016 <sup>[[#fn:r552|552]]</sup> ; Harrison et al., 2018 <sup>[[#fn:r553|553]]</sup> ), although a number of periods of increased and decreased flood activity have been documented for individual glaciers in North America and Greenland, spanning decades (Geertsema and Clague, 2005 <sup>[[#fn:r554|554]]</sup> ; Russell et al., 2011 <sup>[[#fn:r555|555]]</sup> ). A decrease in moraine-dammed glacier lake outburst floods in recent decades suggests a response of lake outburst activity being delayed by some decades with respect to glacier retreat (Harrison et al., 2018 <sup>[[#fn:r556|556]]</sup> ) but inventories might significantly underestimate the number of events (Veh et al., 2018 <sup>[[#fn:r557|557]]</sup> ). For the Himalaya, Veh et al. (2019) found no increase in the number of glacier lake outburst floods since the late 1980s. The degradation of permafrost and the melting of ice buried in lake dams have been shown to lower dam stability and contribute to outburst floods in many high mountain regions (Fujita et al., 2013 <sup>[[#fn:r558|558]]</sup> ; Erokhin et al., 2017 <sup>[[#fn:r559|559]]</sup> ; Narama et al., 2017 <sup>[[#fn:r560|560]]</sup> ).

Floods originating from the combination of rapidly melting snow and intense rainfall, referred to as rain-on-snow events, are some of the most damaging floods in mountain areas (Pomeroy et al., 2016 <sup>[[#fn:r561|561]]</sup> ; Il Jeong and Sushama, 2018). The hydrological response of a catchment to a rain-on-snow event depends on the characteristics of the precipitation event, but also on turbulent fluxes driven by wind and humidity, which typically provide most of the melting energy during such events (Pomeroy et al., 2016 <sup>[[#fn:r562|562]]</sup> ), and the state of the snowpack, in particular the liquid water content (Würzer et al., 2016 <sup>[[#fn:r563|563]]</sup> ). An increase in the occurrence of rain-on-snow events in high-elevation zones, and a decrease at the lowest elevations have been reported (Western USA, 1949–2003, McCabe et al. (2007); Oregon, 1986–2010, Surfleet and Tullos (2013) <sup>[[#fn:r564|564]]</sup> ; Switzerland, 1972–2016, Moran-Tejéda et al. (2016), central Europe, 1950–2010, Freudiger et al. (2014) <sup>[[#fn:r565|565]]</sup> . These trends are consistent with studies carried out at the scale of the Northern Hemisphere (Putkonen and Roe, 2003 <sup>[[#fn:r566|566]]</sup> ; Ye et al., 2008 <sup>[[#fn:r567|567]]</sup> ; Cohen et al., 2015 <sup>[[#fn:r568|568]]</sup> ). There are no studies found on this topic in Africa and South America. In summary, evidence since AR5 suggests that rain-on-snow events have increased over the last decades at high elevations, particularly during transition periods from autumn to winter and winter to spring ( ''medium confidence'' ). The occurrence of rain-on-snow events has decreased over the last decade in low-elevation or low-latitude areas due to a decreasing duration of the snowpack, except for the coldest months of the year ( ''medium confidence'' ).

Il Jeong and Sushama (2018) projected an increase in rain-on-snow events in winter and a decrease in spring, for the period 2041–2070 (RCP4.5 and RCP8.5) in North America, corroborated by Musselman et al. (2018). Their frequency in the Swiss Alps is projected to increase at elevations higher than 2,000 m a.s.l. (SRES A1B, 2025, 2055, and 2085) ( Beniston and Stoffel, 2016 <sup>[[#fn:r569|569]]</sup> ) . This study showed that the number of rain-on-snow events may increase by 50%, with a regional temperature increase of 2°C to 4°C, and decrease with a temperature rise exceeding 4°C. In Alaska, an overall increase of rain-on-snow events is projected, however with a projected decline in the southwestern/southern region (Bieniek et al., 2018 <sup>[[#fn:r570|570]]</sup> ). In summary, evidence since AR5 suggests that the frequency of rain-on-snow events is projected to increase and occur earlier in spring and later in autumn at higher elevation and to decrease at lower elevation ( ''high confidence'' ).

<div id="section-2-3-2-1observed-and-projected-changes-block-5"></div>

<span id="combined-hazards-and-cascading-events"></span>
===== 2.3.2.1.4 Combined hazards and cascading events =====

The largest mountain disasters in terms of reach, damage and lives lost that involve ice, snow and permafrost occurred through a combination or chain of processes. New evidence since SREX and AR5 have these findings (Anacona et al., 2015a <sup>[[#fn:r571|571]]</sup> ; Evans and Delaney, 2015) <sup>[[#fn:r572|572]]</sup> . Some process chains occur frequently, while others are rare, specific to local circumstances and difficult to anticipate. Glacier lake outbursts were in many mountain regions and over recent decades documented to have been triggered by impact waves from snow-, ice- or rock-avalanches, landslides, iceberg calving events, or by temporary blockage of surface or subsurface drainage channels (Benn et al., 2012 <sup>[[#fn:r573|573]]</sup> ; Narama et al., 2017 <sup>[[#fn:r574|574]]</sup> ). Rock-slope instability and catastrophic failure along fjords caused tsunamis (Hermanns et al., 2014 <sup>[[#fn:r575|575]]</sup> ; Roberts et al., 2014 <sup>[[#fn:r576|576]]</sup> ). For instance, a landslide generated wave in 2015 at Taan Fjord, Alaska, ran up 193 m on the opposite slope and then travelled more than 20 km down the fjord (Higman et al., 2018 <sup>[[#fn:r577|577]]</sup> ). Earthquakes have been a starting point for different types of cascading events, for instance by causing snow-, ice- or rock-avalanches, and landslides (van der Woerd et al., 2004 <sup>[[#fn:r578|578]]</sup> ; Podolskiy et al., 2010 <sup>[[#fn:r579|579]]</sup> ; Cook and Butz, 2013 <sup>[[#fn:r580|580]]</sup> ; Sæmundsson et al., 2018 <sup>[[#fn:r581|581]]</sup> ). Glaciers and their moraines, including morainic lake dams, seem however, not particularly prone to earthquake triggered failure (Kargel et al., 2016 <sup>[[#fn:r582|582]]</sup> ).

Landslides and rock avalanches in glacier environments were often documented to entrain snow and ice that fluidise, and incorporate additional loose glacial sediments or water bodies, thereby multiplying their mobility, volume and reach (Schneider et al., 2011 <sup>[[#fn:r583|583]]</sup> ; Evans and Delaney, 2015 <sup>[[#fn:r584|584]]</sup> ). Rock avalanches onto glaciers triggered glacier advances in recent decades, for instance in North America, New Zealand and Europe, mainly through reducing surface melt (Deline, 2009 <sup>[[#fn:r585|585]]</sup> ; Reznichenko et al., 2011 <sup>[[#fn:r586|586]]</sup> ; Menounos et al., 2013 <sup>[[#fn:r587|587]]</sup> ). In glacier covered frozen rock walls, particularly complex thermal, mechanical, hydraulic and hydrologic interactions between steep glaciers, frozen rock and its ice content, and unfrozen rock sections lead to combined rock/ice instabilities that are difficult to observe and anticipate (Harris et al., 2009 <sup>[[#fn:r588|588]]</sup> ; Fischer et al., 2013 <sup>[[#fn:r589|589]]</sup> ; Ravanel et al., 2017 <sup>[[#fn:r590|590]]</sup> ). There is ''limited evidence'' of observed direct event chains to project future trends. However, from the observed and projected degradation of permafrost, shrinkage of glaciers and increase in glacier lakes it is reasonable to assume that event chains involving these could increase in frequency or magnitude, and that accordingly hazard zones could expand.

Volcanoes covered by snow and ice often produce substantial melt water during eruptions. This typically results in floods and/or lahars (mixtures of melt water and volcanic debris) which can be exceptionally violent and cause large-scale loss of life and destruction to infrastructure (Barr et al., 2018 <sup>[[#fn:r591|591]]</sup> ). The most devastating example from recent history occurred in 1985, when the medium-sized eruption of Nevado del Ruiz volcano, Colombia, produced lahars that killed more than 23,000 people some 70 km downstream (Pierson et al., 1990 <sup>[[#fn:r592|592]]</sup> ). Hazards associated with ice and snow-clad volcanoes have been reported mostly from the Cordilleras of the Americas, but also from the Aleutian arc (USA), Mexico, Kamchatka (Russia), Japan, New Zealand and Iceland (Seynova et al., 2017 <sup>[[#fn:r593|593]]</sup> ). In particular, under Icelandic glaciers, volcanic activity and eruptions melted large amounts of ice and caused especially large floods if water accumulated underneath the glacier (Björnsson, 2003 <sup>[[#fn:r594|594]]</sup> ; Seneviratne et al., 2012 <sup>[[#fn:r595|595]]</sup> ). There is ''medium confidence'' that the overall hazard related to floods and lahars from ice- and snow-clad volcanoes will gradually diminish over years-to-decades as glaciers and seasonal snow cover continue to decrease under climate change (Aguilera et al., 2004 <sup>[[#fn:r596|596]]</sup> ; Barr et al., 2018 <sup>[[#fn:r597|597]]</sup> ). On the other hand, shrinkage of glaciers may uncover steep slopes of unconsolidated volcanic sediments, thus decreasing in the future the resistance of these volcano flanks to heavy rain fall and increasing the hazard from related debris flows (Vallance, 2005 <sup>[[#fn:r598|598]]</sup> ). In summary, future changes in snow and ice are expected to modify the impacts of volcanic activity of snow- and ice-clad volcanoes ( ''high confidence)'' although in complex and locally variable ways and at a variety of time scales (Barr et al., 2018 <sup>[[#fn:r599|599]]</sup> ; Swindles et al., 2018 <sup>[[#fn:r600|600]]</sup> ).

<div id="section-2-3-2-2exposure-vulnerability-and-impacts"></div>

<span id="exposure-vulnerability-and-impacts"></span>
==== 2.3.2.2 Exposure, Vulnerability and Impacts ====

<div id="section-2-3-2-2exposure-vulnerability-and-impacts-block-1"></div>

<span id="changes-in-exposure"></span>
===== 2.3.2.2.1 Changes in exposure =====

Confirming findings from SREX, there is ''high confidence'' that the exposure of people and infrastructure to cryosphere hazards in high mountain regions has increased over recent decades, and this trend is expected to continue in the future (Figure 2.7). In some regions, tourism development has increased exposure, where often weakly regulated expansion of infrastructure such as roads, trails, and overnight lodging brought more visitors into remote valleys and exposed sites (Gardner et al., 2002 <sup>[[#fn:r601|601]]</sup> ; Uniyal, 2013 <sup>[[#fn:r603|603]]</sup> ). As an example for the consequences of increased exposure, many of the more than 350 fatalities resulting from the 2015 earthquake triggered snow-ice avalanche in Langtang, Nepal, were foreign trekkers and their local guides (Kargel et al., 2016 <sup>[[#fn:r603|603]]</sup> ). Further, several thousand religious pilgrims were killed during the 2013 Kedarnath glacier flood disaster (State of Uttarakhand, Northern India) (Kala, 2014 <sup>[[#fn:r604|604]]</sup> ). The expansion of hydropower (Section 2.3.1) is another key factor, and in the Himalaya alone, up to two-thirds of the current and planned hydropower projects are located in the path of potential glacier floods (Schwanghart et al., 2016 <sup>[[#fn:r605|605]]</sup> ). Changes in exposure of local communities, for instance, through emigration driven by climate change related threats (Grau and Aide, 2007 <sup>[[#fn:r606|606]]</sup> ; Gosai and Sulewski, 2014 <sup>[[#fn:r607|607]]</sup> ), or increased connectivity and quality of life in urban centres (Tiwari and Joshi, 2015 <sup>[[#fn:r608|608]]</sup> ), are complex and vary regionally. The effects of changes in exposure on labour migration and relocation of entire communities are discussed in Section 2.3.7.

<div id="section-2-3-2-2exposure-vulnerability-and-impacts-block-2"></div>

<span id="changes-in-vulnerability"></span>
===== 2.3.2.2.2 Changes in vulnerability =====

Considering the wide ranging social, economic, and institutional factors that enable communities to adequately prepare for, respond to and recover from climate change impacts (Cutter and Morath, 2013 <sup>[[#fn:r609|609]]</sup> ), there is ''limited evidence'' and ''high agreement'' that mountain communities, particularly within developing countries, are highly vulnerable to the adverse effects of enhanced cryosphere hazards. There are few studies that have systematically investigated the vulnerability of mountain communities to natural hazards (Carey et al., 2017 <sup>[[#fn:r610|610]]</sup> ). Coping capacities to withstand impacts from natural hazards in mountain communities are constrained due to a number of reasons. Fundamental weather and climate information is lacking to support both short-term early warning for imminent disasters, and long-term adaptation planning (Rohrer et al., 2013 <sup>[[#fn:r611|611]]</sup> ; Xenarios et al., 2018 <sup>[[#fn:r612|612]]</sup> ). Communities may be politically and socially marginalised (Marston, 2008 <sup>[[#fn:r613|613]]</sup> ). Incomes are typically lower and opportunities for livelihood diversification restricted (McDowell et al., 2013 <sup>[[#fn:r614|614]]</sup> ). Emergency responders can have difficulties accessing remote mountain valleys after disasters strike (Sati and Gahalaut, 2013 <sup>[[#fn:r615|615]]</sup> ). Cultural or social ties to the land can limit freedom of movement (Oliver-Smith, 1996 <sup>[[#fn:r615|615]]</sup> ). Conversely, there is evidence that some mountain communities exhibit enhanced levels of resilience, drawing on long-standing experience, and Indigenous knowledge and local knowledge (Cross-Chapter Box 4 in Chapter 1) gained over many centuries of living with extremes of climate and related disasters (Gardner and Dekens, 2006 <sup>[[#fn:r616|616]]</sup> ). In the absence of sufficient data, few studies have considered temporal trends in vulnerability (Huggel et al., 2015a <sup>[[#fn:r617|617]]</sup> ).

<div id="section-2-3-2-2exposure-vulnerability-and-impacts-block-3"></div>

<span id="impacts-on-livelihoods"></span>
===== 2.3.2.2.3 Impacts on livelihoods =====

Empirical evidence from past events shows that cryosphere related landslides and floods can have severe impacts on lives and livelihoods, often extending far beyond the directly affected region, and persisting for several years. Glacier lake outburst floods alone have over the past two centuries directly caused at least 400 deaths in Europe, 5,745 deaths in South America, and 6,300 deaths in Asia (Carrivick and Tweed, 2016 <sup>[[#fn:r619|619]]</sup> ), although these numbers are heavily skewed by individual large events occurring in Huaraz and Yungay, Peru (Carey, 2005 <sup>[[#fn:r620|620]]</sup> ) and Kedarnath, India (Allen et al., 2016b <sup>[[#fn:r621|621]]</sup> ).

Economic losses associated with these events are incurred through two pathways. The first consists of direct losses due to the disasters, and the second includes indirect costs from the additional risk and loss of potential opportunities, or from additional investment that would be necessary to manage or adapt to the challenges brought about by the cryosphere changes. Nationwide economic impacts from glacier floods have been greatest in Nepal and Bhutan (Carrivick and Tweed, 2016 <sup>[[#fn:r622|622]]</sup> ). The disruption of vital transportation corridors that can impact trading of goods and services (Gupta and Sah, 2008 <sup>[[#fn:r623|623]]</sup> ; Khanal et al., 2015 <sup>[[#fn:r624|624]]</sup> ), and the loss of earnings from tourism can represent significant far-reaching and long-lasting impacts (Nothiger and Elsasser, 2004 <sup>[[#fn:r625|625]]</sup> ; IHCAP, 2017 <sup>[[#fn:r626|626]]</sup> ). The Dig Tsho flood in the Khumbu Himal of Nepal in 1985 damaged a hydropower plant and other properties, with estimated economic losses of 500 million USD (Shrestha et al., 2010 <sup>[[#fn:r627|627]]</sup> ). Less tangible, but equally important impacts concern the cultural and social disruption resulting from temporary or permanent evacuation (Oliver-Smith, 1979 <sup>[[#fn:r628|628]]</sup> ). According to the International Disaster – Emergency Events Database (EM-DAT), over the period 1985–2014, absolute economic losses in mountain regions from all flood and mass movements (including non-cryosphere origins) were highest in the Hindu-Kush Himalaya region (45 billion USD), followed by the European Alps (7 billion USD), and the Andes (3 billion USD) (Stäubli et al., 2018 <sup>[[#fn:r629|629]]</sup> ). For example, a project to dig a channel in Tsho Rolpa glacier in Nepal that lowered a glacial lake cost 3 million USD in 2000 (Bajracharya, 2010 <sup>[[#fn:r630|630]]</sup> ), and similar measures have been taken at Imja Tsho Lake in Nepal in 2016 (Cuellar and McKinney, 2017 <sup>[[#fn:r631|631]]</sup> ). Other impacts are related to drinking and irrigation water and livelihoods (Section 2.3.1). In summary, there is ''high confidence'' that in the context of mountain flood and landslide hazards, exposure, and vulnerability growing in the coming century, significant risk reduction and adaptation strategies will be required to avoid increased impacts.

<div id="section-2-3-2-3disaster-risk-reduction-and-adaptation"></div>

<span id="disaster-risk-reduction-and-adaptation"></span>
==== 2.3.2.3 Disaster Risk Reduction and Adaptation ====

<div id="section-2-3-2-3disaster-risk-reduction-and-adaptation-block-1"></div>

There is ''medium confidence'' that applying an integrative socioecological risk perspective to flood, avalanche and landslide hazards in high mountain regions paves the way for adaptation strategies that can best address the underlying components of hazard, exposure and vulnerability (Carey et al., 2014 <sup>[[#fn:r632|632]]</sup> ; McDowell and Koppes, 2017 <sup>[[#fn:r633|633]]</sup> ; Allen et al., 2018 <sup>[[#fn:r634|634]]</sup> ; Vaidya et al., 2019 <sup>[[#fn:r635|635]]</sup> ). Some degree of adaptation action has been identified in a number of countries with glacier covered mountain ranges, mostly in the form of reactive responses (rather than formal anticipatory plans) to high mountain hazards (Xenarios et al., 2018 <sup>[[#fn:r636|636]]</sup> ; McDowell et al., 2019 <sup>[[#fn:r637|637]]</sup> ) (Figure 2.9). However, scientific literature reflecting on lessons learned from adaptation efforts generally remains scarce. Specifically for flood and landslide hazards, adaptation strategies that were applied include: hard engineering solutions such as lowering of glacier lake levels, channel engineering, or slope stabilisation that reduce the hazard potential; nature-based solutions such as revegetation efforts to stabilise hazard prone slopes or channels; hazard and risk mapping as a basis for land zoning and early warning systems that reduce potential exposure; various community level interventions to develop disaster response programmes, build local capacities and reduce vulnerability. For example, there is a long tradition of engineered responses to reduce glacier flood risk, most notably beginning in the mid-20th century in Peru (Box 2.4), Italian and Swiss Alps (Haeberli et al., 2001 <sup>[[#fn:r638|638]]</sup> ), and more recently in the Himalaya (Ives et al., 2010 <sup>[[#fn:r639|639]]</sup> ). There is no published evidence that avalanche risk management, through defence structures design and norms, control measures and warning systems, has been modified as an adaptation to climate change, over the past decades. Projected changes in avalanche character bear potential reductions of the effectiveness of current approaches for infrastructure design and avalanche risk management (Ancey and Bain, 2015 <sup>[[#fn:r640|640]]</sup> ).

Early warning systems necessitate strong local engagement and capacity building to ensure communities know how to prepare for and respond to emergencies, and to ensure the long-term sustainability of any such project. In Pakistan and Chile, for instance, glacier flood warnings, evacuation and post-disaster relief have largely been community led (Ashraf et al., 2012 <sup>[[#fn:r641|641]]</sup> ; Anacona et al., 2015b <sup>[[#fn:r642|642]]</sup> ).

Cutter et al. (2012) highlight the post-recovery and reconstruction period as an opportunity to build new resilience and adaptive capacities. Ziegler et al. (2014) <sup>[[#fn:r644|644]]</sup> exemplify consequences when such process is rushed or poorly supported by appropriate long-term planning, as illustrated following the 2013 Kedarnath glacier flood disaster, where guest houses and even schools were being rebuilt in the same exposed locations, driven by short-term perspectives. As changes in the mountain cryosphere, together with socioeconomic, cultural and political developments are producing conditions beyond historical precedent, related responses are suggested to include forward-thinking planning and anticipation of emerging risks and opportunities (Haeberli et al., 2016 <sup>[[#fn:r645|645]]</sup> ).

Researchers, policymakers, international donors and local communities do not always agree on the timing of disaster risk reduction projects and programs, impeding full coordination (Huggel et al., 2015b <sup>[[#fn:r646|646]]</sup> ; Allen et al., 2018 <sup>[[#fn:r647|647]]</sup> ). Several authors highlight the value of improved evidential basis to underpin adaptation planning. Thereby, transdisciplinary and cross-regional collaboration that places human societies at the centre of studies provides a basis for more effective and sustainable adaptation strategies (McDowell et al., 2014 <sup>[[#fn:r648|648]]</sup> ; Carey et al., 2017 <sup>[[#fn:r649|649]]</sup> ; McDowell et al., 2019 <sup>[[#fn:r650|650]]</sup> ; Vaidya et al., 2019 <sup>[[#fn:r651|651]]</sup> ).

In summary, the evidence from regions affected by cryospheric floods, avalanches and landslides generally confirms the findings from the SREX report (Chapter 3), including the requirement for multi-pronged approaches customised to local circumstances, integration of Indigenous knowledge and local knowledge (Cross-Chapter Box 4 in Chapter 1) together with improved scientific understanding and technical capacities, strong local participation and early engagement in the process, and high-level communication and exchange between all actors. Particularly for mountain regions, there is ''high confidence'' that integration of knowledge and practices across natural and social sciences, and the humanities, is most efficient in addressing complex hazards and risks related to glaciers, snow, and permafrost.

<div id="section-2-3-2-3disaster-risk-reduction-and-adaptation-block-2" class="box"></div>

<span id="box-2.4-challenges-to-farmers-and-local-population-related-to-shrinkages-in-the-cryosphere-cordillera-blanca-peru"></span>