For the first time in 20 years, the highest danger level was forecast in large parts of the Swiss Alps in January 2018. Despite 150 destructive avalanches occurring, no lives were lost in settlements or controlled areas. The measures introduced after the extreme winter of 1999, when the occurrence of avalanches was very high, have proven effective. These are the findings of an analysis of incidents in January 2018, produced by the SLF on behalf of the FOEN.
Switzerland has a long history of extreme winters in which avalanches have caused loss of life and property damage. At the same time, however, these occurrences have fuelled progress in protective measures against this natural hazard. Lessons learned gave rise to improved structural defences in avalanche starting zones after the severe winter of 1951 and to the production of hazard maps following the harsh winter of 1968. Later, the focal point shifted to enhancing organisational measures and training for avalanche service employees in the wake of the avalanche winter of 1999.
In the winter of 2018, from 15 January and especially from 21 to 23 January, more than 3 m of snow fell in some localities of the Swiss Alps. The snowfall gave rise to an exceptional avalanche situation. For the first time since 1999, the highest danger level 5 (very high) was forecast for a 36-hour period. Even though January 2018 was far less extreme than February 1999, as regards both snow quantities and avalanche activity, it was the first time since then that the avalanche protection measures were seriously put to the test.
Lessons from 1999 winter translated into action
As in the post-1999 severe winter period, the SLF, with the support of the FOEN (Federal Office of the Environment), has produced a detailed event analysis, this time spanning January 2018. It describes the avalanche situation and losses, examines whether the measures initiated since 1999 proved effective, outlines the findings, and identifies any need for action.
The measures that were called for after the avalanche winter of 1999 were mostly implemented. It was appropriately decided at the time to focus on stepping up the national and regional avalanche warning provisions (publication of the avalanche bulletin twice a day in four languages), training for the safety authorities (two-level courses in three languages), and extending the measuring network (number of IMIS stations almost doubled to 170).
Avalanche protection measures proved successful
For many decades the public sector has been taking action to reduce the avalanche risk within the framework of an integrated risk management programme. The implemented structural (avalanche defences), organisational (avalanche warnings, closures), planning (hazard maps) and biological (avalanche protection forests) measures have reciprocal effects.
The 2018 event analysis shows that 150 avalanches caused damage to buildings, transportation routes, vehicles, power lines, transport infrastructure, forests, or fields and meadows in the period from 3 to 23 January 2018. In isolated instances, avalanches were released from starting zones with supporting structures that actually are expected to prevent avalanche release. This illustrates that there is no absolute protection against natural hazards. Fifty-three avalanches prompted missions to clear snow or search for possible victims. No lives were lost in settlements and secured areas. For comparison: In the avalanche winter of 1999 there were 17 fatalities, in the avalanche winter of 1951 even 95 fatalities in settlements and secured areas.
In conclusion, while bearing in mind that a direct analogy is impossible in view of the smaller quantities of snow in January 2018, the post-1999 optimisation measures passed the most recent critical test.
High demands placed on avalanche services
The principal burden arising from an exceptional avalanche situation rests with the local avalanche services maintained by the district authorities, railway operators and civil works departments. They evaluate the danger on the ground and respond accordingly by initiating closures, artificial avalanche triggering and, if necessary, evacuations. The avalanche services managed the demanding avalanche periods successfully overall. The high-altitude and variable snowfall level in January 2018 presented an additional challenge because the precipitation often fell as rain in intermediate and low altitude zones, and triggered landslides, debris flows and rockfalls. In many places the avalanche services also had to assess the danger of gliding avalanches, which is an especially demanding exercise, given the difficulty of predicting them and the lack of extensive research on the subject to date.
Exceptional avalanche situations and climate warming
During the period of heavy snowfall in January 2018, rain fell up to high altitudes repeatedly. The high zero degree level and rainfall up to high altitude zones could be erroneously interpreted as indications of climate warming.
The existence of a relationship between a single event, such as the avalanche situation in January 2018, and climate change cannot, however, be deduced. In the winter of 1999 as well, the snowfall level intermittently rose above 2000 m, on 19/20 February.
During the heavy snowfall period this year in January, the temperatures were consistently low. A comparison of the two heavy snowfall periods, in 2018 and 2019 respectively, clearly shows that the temperature at relatively low altitudes exerted a substantial influence on the flow behaviour and runout of the avalanches. While most avalanches in January 2018 were wet in the runout zone, numerous powder avalanches occurred in 2019, some of which damaged forests and travelled long distances along the valley floor.
The effect on future avalanche activity of further progressive warming and the marginally different precipitation regime, in particular in case of heavy snowfall, currently remains unclear. It is therefore too early to revise the risk management arrangements.
In order to cope with further exceptional avalanche situations successfully, the high standard of avalanche protection that exists in Switzerland must be maintained by all parties – the federal government, cantons, district authorities and local avalanche services. The measures initiated after the extreme winter of 1999 must therefore be continued with the support of longer-term financing safeguards. The continuous maintenance of structural avalanche defences and systematic management of avalanche protection forests are likewise important. Heightened safety requirements also call for the local avalanche services to become even more professional overall.
The task of responding to gliding avalanches and individual new phenomena, such as “slushflows”, is presenting the avalanche services with major challenges. Research into the causes and temporal evolution of gliding snow needs to be stepped up. The analysis also reveals a need to examine in greater detail the influence of climate change on future avalanche activity.