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A v a l a n c h e

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D a t a

AvalancheForecastingwithGIS
R.Bolognesi¹,M.Denuelle²,L.Dexter²

1 _{Swiss Federal Institute for Snow and Avalanche Research, Davos, Switzerland}

2 _{Department of Geography,Northern Arizona University, Flagstaff, Arizona}

Key words : Local Avalanche Forecasting, Geographic Infor-

mation System

INTRODUCTION

Avalanches depend on snowpack stability as well as ter-
rainconditions.Thus,thesetwokindsofinformation
are required to performpunctual predictions.However,
ifthesiteisverylarge,includingmanygulliesand
slopes,itmaybedifficulttodefinethestartingzone.
Therefore,a detailed topographic analysisofthe site is
useful.Thisanalysiscan be done by a Geographic Infor-
mation System(GIS).
This paperpresents anidea: using a GIS to determine
and describe the starting zone(s) of a large avalanche site
in order to provide computed inputs to a local avalanche
forecasting model.
This model is the NxLog system,which was designed
at the Swiss Federal Institute for Snow and AvalancheRe-
search (Bolognesi,1994).NxLog is an expert systemrun-
ningsymboliccalculationsaswellasnearestneighbor
procedure. The aim of this system is to provide every day
the probability of avalanche occurrence foreach starting
zone of a defined area (a ski resort for example). Is it pos-
sible and profitable to make the GIS and NxLog work to-
gether ? This is the question we want to answer.

1. GISIMPLEMENTATION
   
   The source of information used for the topographic analy-
   sis ofthe avalanche sites istheDigital ElevationModel
   (DEM).Such DEMs are useful forany terrain analysis or
   representation. The data included in the DEMs iseleva-
   tion, and geographical coordinates. Using a GIS software,
   this data can be derived into slope angle and slope aspect.
   Withslopeaspect,slopeangle,andelevation,atopo-
   graphic representation and analysis of any avalanche site
   can be done in greater precision.The minimum size unit
   of terrain of such data is 30x30 meters cell which isthe
   standard format of a DEM in the USA.The GIS software
   used to derive the data in slope aspect,slope angel,and
   elevation isthe GRID module of ArcInfo^{T M} .The GIS im-
   plementation can be divided into two steps.
   The first step is to create the three layers (slope aspect,
   slope angle, and elevation) from the DEMs. After creating
   those layers with GRID,we divide each layerinto inter-
   vals ofcriticalimportance foravalancherelease.These
   intervalswaschosenaccordingtoexperts'opinion
   (K.Birkeland, R.Bolognesi, L.Dexter, A.Gleason, D.Hogan).
   The slope aspect layer is broken down into 8 intervals
   of 45degrees each representing North,North East,East,
   SouthEast,South,SouthWest,West,NorthWest.The
   slopeanglelayerisdividedinto9intervals.Theeleva-

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