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Type d'article : collaboratif (CC by-sa)

How does YETI work?

The application relies on risk reduction methods and a cartographic interface. By analyzing key variables (inclination of the slope, orientation ...) YETI makes it possible to visualize the main slopes at risk according to the level of hazard announced by the avalanche bulletin.

The reduction methods used in the application are according to the user's choice:

• The Beginner Reduction Method (MRD)
• The Elementary Reduction Method (MRE)
• The Professional Reduction Method (MRP)

Read below: How to choose the relevant reduction method?

To learn more on the avalanche risk reduction methods:

• P. Descamps and O. Moret, Avalanche, comment réduire le risque, éd. Paulsen, 2016
• W. Munter, 3X3 avalanches, la gestion du risque dans les sports d’hiver, éd. du Club alpin suisse, 2006
• S.Harvey, H.Rhyner et J.Schweizer, Avalanches, mieux les comprendre, éd. du Club alpin suisse, SLF, 2013
• White risk: https://whiterisk.ch

Where can YETI be used?

YETI works in all the Alps, Pyrénées, Auvergne, Tatras and all areas from Norway and Iceland where an avalanche bulletin is available.

Do you need to be online in order to use YETI?

YETI processes a risk map for each request with all parameters selected by the user (risk reduction method, avalanche bulletin level...). YETI does not work offline.

Who is the application YETI for?

YETI has been built for anyone who wants to manage avalanche risk instead of undergoing it. To make the most of YETI, one must accept to question its intuitions and reason from objective data.

A minimum knowledge of the use of the 3X3 analysis grid and reduction methods is advised to appreciate the interest and measure the limits of YETI.

Its use requires an outing preparation time at home or at the shelter from 15 minutes to 1 hour.

For more information on risk analysis with the 3X3 grid, refer to the literature cited in question 1.

Risk analisys	Group	Terrain	Conditions
At home or in the mountain hut	- Group size - Experience, competences - Responsability, expectations - Reduction method choice	- Maps, topoguides - Timing, slopes, orientations - Situations to be avoided - Yeti	- Avalanche bulletin - Automatic weather station - Typical avalanche problems - Recent informations from mountain guides or social media
	OK ? unless ok, cancell or plan B
During the approach	- Group fitness - Group composition change - Avalanche tranceiver check - Time check	- map/field comparison - Attendance, tracks	- Weather conditions (wind, T°, snowfall or rainfall) - Critical depth of new fallen snow - Alarm signals
	OK ? unless ok, return home
In the slope	- Fitness, motivation, discipline - Time control - Safety spacing or spacing distances - Downhill corridor	- Track quality, terrain configuration - Real slope and orientation - Other objective dangers	- Visibility, weather conditions - Warming, humidification - Critical depth of new fallen snow - Alarm signals

Is the YETI application enough to prepare an outing?

The YETI application should be used in addition to a risk analysis conducted using the 3X3 analysis grid. This analysis grid analyses the 3 main risk factors (conditions, terrain and group) at three key moments during an outing: during preparation at home, during the approach and right before key crossings.

Always keep a critical eye on the information given by the application (read below: What are the limits of YETI?).

What is the interest of YETI?

The art of mountaineering and mountain skiing is to navigate a potentially dangerous environment while reducing the risks.

During preparation at home, YETI makes it possible to distinguish immediately the riskiest slopes and to easily identify the key passages of a route. Validating an outing choice and imagining fallback options are made easier thanks to the overall view of the cartographic interface.

With YETI, outing preparation consists of sneaking into less risky areas, favouring slopes with the lowest (but never zero) probabilities of tripping, or, for the more adventurous, taking an informed risk.

YETI does not issue a green light or a red light. YETI gives information on the greater or lesser probability of triggering slopes in order to guide your outing choices according to the expected snow conditions.

Can the YETI application be used on the ground?

YETI is a decision support tool for preparing an outing at home.

In the field, the practitioner has new and concrete information about the conditions, the terrain and the group. As the group progresses, the analysis of the real data confirms, nuances or modifies the assumptions made at home with the help of YETI. Tools such as 3X3, the critical amount of fresh snow, warning signs, sticks to measure the slope are then more useful than the YETI application to decide.

In the field, the good questions to ask yourself include:

• Are there any alarm signals?
• Is the critical amount of fresh snow exceeded?
• Does visibility lead to insightful risk analysis?
• Is the terrain configuration favourable or unfavourable?
• Is it possible to make a safe trace?
• Are the participants motivated and have the level for the outing?
• etc.

Clear answers to these questions are needed to make a good decision on the approach and in the key passages. It requires solid training and a few years of practice.

What are YETI limitations?

The main limitations of this tool are linked to the pillars on which it is based: the avalanche bulletin, the digital terrain model, the reduction methods and the algorithm used.

The limits of the altimetric data : the process is based on altimetric data from differents countries where Yeti is available. Those data have different resolutions, précisions and accuracies. Moreover, data from different countries have been merged on the borders. This may lead to artefacts along the national borders. This accuracy is most of the time enough to assess the inclination of the key passages of a ski or snowshoe route. However, under certain circumstances, slopes reduced to less than 25 meters may already be dangerous. It is advisable to remain vigilant on the ground while maintaining a critical spirit compared to the information given by YETI.

To know more : FR - Slopes more than 30° on IGN’s Geoportail: Use, interests and limits for snow sports enthusiasts

The limits of the avalanche bulletin: the avalanche bulletin draws up an inventory of the avalanche hazard at the scale of a massif outside the marked tracks. The conditions of a valley (and even less of a slope) are not evaluated by the avalanche bulletin. The danger level from 1 to 5 is the summary of a more complex situation described in the text that accompanies the bulletin. Reading this text is one of the pillars of risk analysis with the 3X3 grid, which must always precede the use of YETI. The entry of the danger level in YETI assumes that the practitioner has read the entire newsletter: text, wind rose, recent amount of fresh snow ... Finally, the bulletin is broadcasted in France only from December 15 to April 30 while the exposure to the hazard can take place all the year notably in high mountain. There are tools to refine and, if necessary, correct the information in the avalanche bulletin. Refer to the literature cited in question 1.

The limits of reduction methods: reduction methods rely on numerous sedimented experiments through accidentology from which we can draw some lessons through probabilities. This sum of experiences will always be greater than the experience of one person, even experienced. However, it is still possible to cause or experience an avalanche, including on a slope not identified as "at risk" by a reduction method. The practitioner of the snowy mountain must make a reasoned and critical use of YETI and the tools at his disposal to evaluate the risk. He remains responsible for home-based analyses, decisions made in the field, his actions and their consequences. The authors and partner institutions of the project can not be held responsible for accidents occurring during practice after using the YETI application.

The limits of the algorithm used by YETI: in the current state of development, only the slopes considered as "at risk" by the reduction methods (MRD, MRE or MRP) are displayed with a colored fading. However, starting from the danger level 3, it is advisable to consider the steep slopes which dominate the envisaged route because they are likely to be triggered remotely. From danger level 3, the absence of blurring does not mean that the route is safe. Check the slopes that dominate the route and make sure they do not directly threaten the trail.

In the above example, by risk 3, if we go up the valley towards the lake, we are permanently dominated by slopes considered as at risk (dark blue right bank, light blue left bank). An avalanche departure from danger 3 may occur in less steep terrain where there is no color fading.

How to choose the relevant reduction method?

The beginner reduction method (MRD)

The Beginner Reduction Method (MRD) is for practitioners with little experience of snow outside marked trails. An experienced supervisor preparing an outing for beginners will be interested in using this method in order to create a margin of safety adapted to a public who progresses more slowly with frequent falls (solicitation of the snowpack). Areas considered to be at risk are shown in light blue.

The elementary reduction method (MRE)

The Elementary Reduction Method (MRE) is suitable for experienced practitioners who want to maintain a comfortable margin of safety. With the MRE, you can fill a good skier's life by enjoying powder snow in winter and the best snows in spring. It has been adopted by experienced guides who consider it sufficient to indulge in exercising their profession in a more relaxed way.

Areas considered to be at risk are represented by two shades of blue:

• dark blue for slopes at risk in orientations checked on the wind rose
• light blue for other slopes at risk

The professional reduction method (MRP)

The professional reduction method (MRP) offers a greater choice of outing in the field, especially on a steep slope, but reduces the margin of safety. It requires a more detailed understanding of the snowpack and involves parameters such as slope orientation, route use and precautionary measures considered during the outing. It is aimed at experienced practitioners who feel too limited by the MRE.

The slopes at risk are represented by two colors:

• residual risk less than 1: no color fading
• residual risk between 1 and 1.5: purple
• residual risk > 1.5: purple

How to use YETI with the MRD?

Select the beginner reduction method (MRD) in the choices’ list. Select the predicted danger level from the avalanche bulletin, from 1 to 3. Level 4 cannot be chosen if you are using the MRD. If needed, mention the altitude limit from which the level of danger would increase. Zoom on the studied massif, valley or slope. Turn on the IGN map by clicking on the blue computer icon at the bottom left of the page. Submit your request by clicking on « Compute Risk ». The application displays the slopes at risk with a color code on a cartographic interface. The legend is accessible by clicking on the "Legend" icon at the top right of the map.

• If no fading appears, it is possible to do the outing within reasonable safety conditions. Once on the field stay wary if your surroundings or the size of the group evolve. Pay attention to the slopes that dominate your itinerary if you obtain a level 3 hazard or more (risk of remote triggering).
• Light blue colour: slopes at risk, to avoid. From danger level 3, consider the blue coloured slopes which dominate the route.

How to use YETI with the MRE?

Select the elementary reduction method (MRE) in the form. Enter the level of danger announced by the avalanche bulletin, from 1 to 4. If necessary, mention the altitude limit from which the danger evolves. Report the critical orientations given in the compass rose in the bulletin. Zoom in on the massif, valley or slope concerned. Activate the IGN map by clicking on the blue icon at the bottom left of the map. Submit the request by clicking on "Compute risk". The application displays the slopes at risk with a color code on a cartographic interface. The legend is accessible by clicking on the "Legend" icon at the top right of the map

• No color fading: the project is valid. Remain vigilant in the field if the conditions or the size of the group change. Beware of the slopes which dominate the route from danger level 3 (risk of remote triggering).
• Light blue color: risky slope
• Dark blue color: increased risk due to orientation

How to use YETI with the MRP?

Select the professional reduction method (MRP) in the form.

• Enter the hazard potential from 1 to 16.
• If you estimate that the snowpack will be wet, check the "wet snow" box (rain, sun and heat especially in spring). In such conditions, the algorithm considers that the danger is NOT orientaiton dependent. If the box is not checked, the MRP will add reduction factors for south orientations : RF = 2 if the mountaineer accepts not to go in sector 315°-45°, RF = 3 for sector 292.5°-112.5°.
• Specify the size of the group and the precautionary measures envisaged.
• Zoom in on the massif, valley or slope concerned.
• Activate the IGN map by clicking on the blue icon at the bottom left of the map.
• Submit the request by clicking on "Compute risk".

The application displays the slopes at risk with a color code on a cartographic interface. The legend is accessible by clicking on the "Legend" icon at the top right of the map.

• No color fading: residual risk <less than 1. Low risk, relatively safe in the absence of other hazard indicators. Remain vigilant in the field if the conditions or the size of the group change. Beware of the slopes which dominate from danger 3 (risk of remote triggering).
• Mauve color: residual risk between 1 and 1.5. Increased risk, caution, training and experience are necessary in order to adopt a defensive attitude by taking precautionary measures to reduce the risk. Safer than expected local snow conditions or favorable terrain configuration are required to continue this route.
• Purple color: residual risk greater than 1.5. High risk, it is better to give up on this outing.

Who are the designers and partners of the YETI application?

The application was first developed in the form of a demonstrator using Qgis software. The development was carried out by engineering students and teacher-researchers from the ENSG-Géomatique as well as by developers of the IGN Geoportal.

The Petzl Foundation accompanies and supports the project.

The Camptocamp.org website welcomes and facilitates the launch of the application.

Personal data

No data is kept on the server. At the end of each request, all temporary data is destroyed. The requester's IP address is not retained.

A question, a remark, a request for clarification, who to contact?

For more information, you can contact Jacques Beilin or Olivier Moret