M a n a g e m e n t

a n d

A n a l y s i s

o f

S n o w,

A v a l a n c h e

a n d

C l i m a t e

D a t a

• Dailyconventionalsnowand avalanche observations
  since the beginning of the AvalancheWarning Service
  in Switzerland (80 observers)
• Every fortnightdetailedsnow profiles andRutschblocks
  from the observers
• Hourlyreadingsfrom30automaticweatherstations
  (ANETZ) above 2500 m
• Personalinformationsandreportsaboutsnowcover
  conditions,etc. by professionals (mountain guides, al-
  pine lodge keepers,etc.)
  
  The bulletin text is structured in four subsequent para-
  graphs:
• General informations:weather and snow situation
• Snow coverconditions:structure, layering and stabil-
  ity of the snowpack
• Hazard level: 1 - 5, accordingto theEuropeanAvalanche
  Hazard Scale
• Trends:covering the next 24 to 48 hours

The original languageof the avalanchebulletin is German,
translations into French and Italian are performed before
distributing the bulletin via phone, telex, fax, teletext and
the World Wide Web. Additionally,two general maps on
the averagesnow depth and the distribution of the hazard
levels in the different bulletin regions can be obtained by
GIS (scale 1:1'000'000) (Schöning 1992).

THE LAWIPROG-MODEL

The Swiss avalanche bulletin uses topographicaland mor-
phological features to describe the hazard areas: altitude,
slope, aspect and morphological elements like ridges, gul-
lies and basins.Depending on how those features are ex-
pressed and how they recombine fora given location the
resulting hazard levels may vary considerably.For exam-
ple:If the terrain is steep and the aspect considered haz-
ardous but the location situated below the critical altitude,
the avalanchehazard may be lower becauseof the eventual
higher snowpack stabilityat lower altitudes. On the other
hand backcountry skier will be save even under hazardous
conditions and in high altidudes if the inclination of the
terrain does not get close to the critical values.
Hence a simple multiplicative model for avalanchehaz-
ard mapmodelingwas implementedon ARC/INFOina
first approach.
Themaininput data forLAWIPROG isahigh resolu-
tion digital terrain model (DTM) with a cellsize of 25 me-
ters (Swiss coordinate system,scale 1:25'000).Each mesh
point in this net represents a different altitude above sea-
level,looking like a fishnet,folded in the form of the ter-
rain's surface (see Fig. 1).Fromthis rasterdata set (grid)
the datafor slope, aspectandaltitudeare derivedandsaved
as separate data layers.To furtherprocess these data the
map algebra language of the rastermodule GRID is used
(Tomlin1990).Anymathematicaloperationorfunction
can be appliedto either a singleor various grids in order to
derive a result grid (see Fig. 1).
To calibratetheinput data fortheLAWIPROG-model
according to theirsignificance forthe hazard prediction,
weight factors were developed (see Fig. 2 - 4). A semantic
analysis showed,that the main part of the bulletin-text is

2

structuredin hazardlevels andexplanatory sentencesabout
the critical terrain features altitude, slope and aspect.

Fig 1: Derivation and multiplication of the three weight grids

Data Calibration

• Hazard Level P_HL
  
  As the hazard level represents the main result of the bul-
  letin - snowpack stability - it weighs a priori twice as much
  as the other input data. Values between 2 and 10 are pos-
  sible.In present prototype the regions are not yet differ-
  entiated.All cellsin the resulting hazard grid (PHG) get
  the same weight factorforthe hazard level.
  
  The following data are weighed according to their signifi-
  
  cance in the actual bulletin, using a scale from 1 to 5.

• Altitude

• Slope

• Aspect

P_ALT

P_SLP

P_ASP

Once all data are ready, thepredictedhazard map (grid)
can be calculated according to the following formula:

PHG= P_HL

* P_ALT

* P_SLP

* P_ASP