The aim of this work is to produce an avalanche hazard map with ArcGIS and to compare it with the map of possible avalanche location (CLPV, Carta di Localizzazione Probabile delle Valanghe), which is based on past events. The map will be based mainly on morphological characteristics and on their link with the possibility of avalanche generation. The avalanche evolution and movement are not considered, as well as the risk (probability of harm or economic loss with respect to people).

1. Fundamental of GIS
ArcGIS Project:
Avalanche Hazard Map
Daniela Carrion
Omid Habibzadeh Bigdarvish (836722)
Daniel Jalili (832852)

2. 2
Introduction
An avalanche (also called a snowslide or snowslip) is a rapid flow of snow down a
sloping surface. Avalanches are typically triggered in a starting zone from a mechanical
failure in the snowpack (slab avalanche) when the forces on the snow exceed its
strength but sometimes while gradually widening (loose snow avalanche). They are
unpredictable and often small scale of it can lead to devastating results. Avalanche
cartography deals with the causes and consequences of such incidents and tries to
depict them in a variety of ways. The most common cartographic representation within
this field is the avalanche hazard map. Avalanche hazard map is an indispensable tool
for evaluation of avalanche danger.
The effective parameters on the formation of avalanche, based on the literature are
considered to be morphology, existence or nonexistence of forests and also
wind effect. The morphology of the area affects an avalanche in two different ways.
1. Slope of the area
2. The direction of the region relative to the direction of sunlight in different seasons
Position of the sun in relation to the area.
In the case of slope, different researchers have proposed different criteria. In the
present work a slope between 28 and 55 degrees is considered as Morphologic hazard.
Also a sudden variation in slope of greater than 10 degrees is considered as an
escalating condition. The reason for this criteria is that on slopes lower than 28
degrees, no movement of the accumulated snow is possible and on the contrary, on
slopes higher than 55 degrees, there is no chance of formation of thick layered snow
and hence, no chance for the initiation of avalanche in these areas.
The other thing about the morphology of the area which can negatively affect the
occurrence of an avalanche is that during winter, due to the direction of the sunlight,
the snow mass accumulated on the northern aspect loses its stiffness, becomes watery
and therefore is more prone to slip. There is also same condition for south and east
in spring. The figure below shows how morphological slope properties affect
avalanche.

3. 3
“Morphological Slope Properties Affecting Avalanche”
Interpretation of the data:
In order to produce an avalanche hazard map with ArcGIS and to compare it with the
map of possible avalanche location (CLPV, Carta di Localizzazione Probabile delle
Valanghe), which is based on past events.
The map will be based mainly on morphological characteristics and on their link with
the possibility of avalanche generation. The avalanche evolution and movement are
not considered, as well as the risk (probability of harm or economic loss with respect
to people).
NOTE: this work is a reasonable exercise based on scientific literature. The very
complex topic of avalanche hazard is not treated in a comprehensive way.
The model considered to produce the avalanche hazard map takes the following
factors into account:
 Morphologic hazard. Based on the following conditions:
o slope between 28° and 45°÷55° (depending on literature sources)
o slope variation larger than 10° (presence of break lines)
 Morphologic hazard aggravating circumstances:
o S-E aspect: aggravating circumstance during spring
o N aspect: aggravating circumstance during winter

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 Forest coverage. The presence of vegetation can NOT stop the avalanche once
it’s started, but the vegetation coverage interferes with the creation of compact
and homogeneous snow layers
o dense evergreen forest (spruce or spruce with larch)
o sparse wood or deciduous dense wood (larch)
o bare or covered by grass or sparse vegetation (pasture or bushes)
 Wind effect (aggravating circumstance): downwind hazard with respect to the
wind prevailing direction (factor suggested by a mountain guide).
(Meyer-Grass M., Imbeck H., 1987)
Available data
The area of interest is Val di Pejo area (north western part of Trentino Region,
northern Italy)
 Contour lines with 10m spacing (they have been obtained from the regional
base map)
 Forest coverage: two maps are available, comp7 and cveg
 Aerial photo, to be georeferenced
 CLPV (Carta di Localizzazione Probabile delle Valanghe): map of possible
avalanche location, which is based on past events. It is based on a 1:25000
scale map.
 Regional base map, 1:10000 scale.

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 Caldes station (46°22′0″N 10°57′0″E): the wind is more intense in the early
afternoon, with NE-E prevailing direction, during the rest of the day the
prevailing direction is SW-W.
Maps to be produced
 DTM
 slope map
 slope variation map
 aspect map
 If needed, more than one avalanche hazard map can be produced considering
different conditions.
Explanation of the project:
Digital Terrain Model (DTM):
Digital terrain model is a topographic model of the bare earth terrain relief that can
be employed by computer programs. In this case, the digital terrain model is a digital
model of a terrain's surface which is created from terrain elevation data with regular
grid (raster format). The values are stored in a matrix. Compared to the vector format,
the files of raster format can make simpler and faster data processing, and the
cartographic representation system can be easily changed and also the cartographic
information can be better visualized.
Basic Map:
The first map to be produced is the DTM map. Considering the contour lines that were
given, interpolation was carried out to make the height map of the region. It is
noticeable that some correction was done manually on the contour lines as in a small
region the altitude given by the contours did not match with the aerial photo given
before.

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Slope Map:
A map indicating the topography of an area along with an analysis of topographic
features as they have influenced and may continue to influence land development.
At this step, spatial analyst tools have been used to produce the Slope map. In this
method, first the hazardous regions with slopes with 28 and 55 were identified then
break lines are also take into accounts. As a results the two maps (28<slope<55 and
slope variation larger than 10 degrees) were used and with help of raster calculator
tools and neighborhood tools, the block statistics were produced.

7. 7

8. 8
“Slope between 28° and 55”
“Slope variation larger than 10° “
Aspect Map:
The slope maps is not enough to identify the direction of the slopes. Hence, the aspect
map was produced by the spatial analyst tool from aspect tools. The direction of the
slopes was needed as some criteria were dependent on the orientation of the slopes.
In physical geography, aspect generally refers to the horizontal direction to which
a mountain slope faces. For instance, a slope on the eastern edge of
the Rockies toward the Great Plains is described as having an easterly aspect.

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“Aspect Map”
Aggravation map:
The morphological hazard aggravating conditions has been evaluated. This part
contains two maps, one for winter and the other one for spring. In winter, the
aggravating condition occurs in north direction while in spring, this condition is true
for south and east direction. To obtain these maps the raster calculator tools based
on the aspect data has been used.
“Winter aggravating condition”

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“Spring aggravating condition”
Wind aggravation map:
According to the wind direction aggravating condition, two maps have been produced.
The wind is more intense in the early afternoon, with NE-E prevailing direction, during
the rest of the day the prevailing direction is SW-W. One map represents the
aggravating condition in the early afternoon and the other one represents it in the
other times of the day. These maps all have been produced by raster calculator tools
based on the aspect data.

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“Wind Map_ Early Afternoon”
“Wind Map_ Rest of the Day”
Vegetation map:
The other effective factor is the coverage by forests. To take this factor into account,
a vegetation map has been provided which describes the vegetation protection
capability against avalanches with three classifications, dense forests, sparse wood or
copes and pastures. A dense forest prevents the occurrence of an avalanche by
preventing the compactness and formation of dense snow layers although it fails to
stop an avalanche after it starts moving. The helpful region was derived from the
complete forest coverage map.

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“Forest Coverage Map”
Avalanche Hazard map production:
Eventually in this project there will be two different hazard map which have been
produced according to various situation in the spring and winter. To produce the final
avalanche hazard map the following procedures have been taken; In the case of spring
season there will be slope mix map, vegetation coverage map, wind effect map and
aggravating circumstances during spring, which will conclude avalanche hazard map
in spring. The same procedure should be taken for the avalanche hazard map in winter
considering aggravating circumstances during winter plus three other maps in spring
case.
Hazard Map Production:
Slope:
Now the mixed slope hazard map can be produced. This map was created by
combining slope variation map greater than 10°, and the slope map between 28° and
55 ° multiplied with “2” to distinguish the importance of the different values of the
two maps by using Raster Calculator.
Then the mixed slope map was reclassified to three classes:
1. 0 for the areas that have no slope between 28-55 and variation smaller than
10.
2. 35 for areas that have slope between 28-55 and variation smaller than 10.
3. 45 for slope between 28-55 and variation larger than 10.

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(This step has been done in order to distinguish the different values and
importance of different aspects).
“Mix Slope Map”
Morphological hazard aggravating circumstances:
The two previous morphologic maps that produced for the aggravating condition in
different seasons have been reclassified to values: 0 and 15.
(This step has been done in order to distinguish the different values and importance of
different aspects).
Wind Effect:
In order to produce the map for wind, it has been decided to consider both maps
produced for the wind effect in a single map and combined them to give us hazards
in whole 24 hours. By this assumption, the winds that blow in the early afternoon were
not separated from the winds that blow in the rest of the day and they were all
together. After that we reclassified the class values to : 0 and 15.
(This step has been done in order to distinguish the different values and importance of
different aspects).

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“General Wind Map”
Vegetation Coverage:
The vegetation data includes four classes: Dense evergreen forest, sparse wood or
copse, Bare or covered by grass or pastures, No data. Different weight have been
given to each class by using ‘Reclassify’:
(This step has been done in order to distinguish the different values and importance
of different aspects).
1) High forest= -10.
2) Copse= 10.
3) Pasture= 35.
4) No data= 0.
Final Avalanche Hazard Maps:
In order to producing the final hazard maps, weights to each of the aspects have been
given with reclassification of values in any single map and then all the maps have been
together, the results are demonstrated in the following figures :
Hazard map in winter includes reclass mixed slope, reclass forest vegetation, reclass
wind+ reclass aggravating condition.
Hazard map in spring includes reclass mixed slope, reclass forest vegetation, reclass
wind, reclass aggravating condition.

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“Avalanche Hazard Map for spring”

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“Avalanche Hazard Map for winter”
Conclusion:
Based on the results, the avalanche hazard is almost similar for the two seasons with
more hazardous in spring map. Although it is clear that the hazard is generally higher
on the east and west part of the region with higher altitudes and steep slopes.

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Comparison with CLPV:
Avalanche hazard map with the map of possible avalanche location (CLPV) need to be
compared based on previous events to evaluate the accuracy for the hazard map
which have made.
For this reason, by overlapping the avalanche hazard map with the CLVP, the accuracy
of the hazard maps can be evaluated by checking whether all the reported avalanches
have been included in the hazardous area defined in the global hazard map.
“Comparison Map for spring”

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“Comparison Map for winter”
From the overlapping maps of the avalanche hazard and the CVLP, we can notice that
most of the reported avalanches have been included in the hazardous areas. As a
result, the avalanche hazard map has been obtain using ArcGIS corresponds the real
condition and that can be considered as a precise estimation.

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References:
Pistocchi A., Notarnicola C. (2013), Data-driven mapping of avalanche release areas:
a case study in South Tyrol, Italy, Natural Hazards, Volume 65, Issue 3, pp 1313-1330
Ciolli M., Zatelli P. (2000), Avalanche risk management using GRASS GIS, 1st Italian
GRASS users meeting proceedings, Geomatics Workbooks, Vol 1,
Cresta R., Telmon G. (1980), Nozioni elementari sulle valanghe, Servizio Valanghe
Italiano
Siebert W. (1985), Nozione sulle valanghe, Associazione Guide Alpine sciatori – Alto
Adige