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

===== 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).

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'''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>
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'''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.'''
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[[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.

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