Development of avalanche hazard maps by ArcGIS for Trentino (Alpine Italy)

Fundamental of GIS
Avalanche Hazard Assessment
Submitted By:
Maryam Izadifar (814117)
Alireza Babaee (814217)
Submitted To:
Prof. Daniela Carrion
M.Sc Civil Engineering for Risk Mitigation
June 2014

Fundamental of GIS - Avalanche Hazard Assessment Politecnico di Milano
Maryam Izadifar M.Sc. in Civil Engineering
Alireza Babaee For Risk Mitigation (CERM)
1
Table of Contents:
1- Introduction............................................................................................................................. 2
1-1- Aim of Project.................................................................................................................. 2
1-2- Model Criteria .................................................................................................................. 2
2- Project Data............................................................................................................................. 7
2-1- Site Location .................................................................................................................... 7
2-2- Available Data.................................................................................................................. 9
3- Produced Maps...................................................................................................................... 10
3-1- DTM............................................................................................................................... 10
3-2- Morphologic Hazard Map.............................................................................................. 13
3-2-1- Slope Map.................................................................................................................. 13
3-2-2- Slope Interval Map..................................................................................................... 14
3-2-3- Break Lines Map........................................................................................................ 15
3-2-4-Morphologic Hazard Map........................................................................................... 16
3-3- Aspect Maps................................................................................................................... 17
3-3-1- Slope Aspect with respect to the sun.............................................................................. 17
3-3-2- At mid latitudes in the northern hemisphere .................................................................. 18
3-3-3- Aggravating Circumstances....................................................................................... 19
3-4- Vegetation Map..................................................................................................................... 23
3-5- General Hazard Map............................................................................................................. 25
3-6- Aspect Hazard Map............................................................................................................... 26
3-7- Final Hazard Maps and Conclusion...................................................................................... 29
4- Georeferencing...................................................................................................................... 34
5- References............................................................................................................................. 38

2
1- Introduction
1-1- Aim of Project
The aim of this work is to produce an avalanche hazard map with ArcGIS - ArcView and to
compare it with the map of possible avalanche locations, which is based on past events, for the
Val di Pejo which is located in the north western part of Trentino an Italian alpine region that
shows frequent and sometimes huge avalanches.
The map will be based mainly on morphological and vegetation 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).
The last version of ArcView 10.2 has been used in this study.
1-2- Model Criteria
Avalanche is considered as one of the greatest sources of concern in many mountainous areas
which can lead to catastrophic damages to human lives, infrastructures and local business
activities. The increasing use of land in mountain areas requires intensive protective measures, in
particular the application of hazard zoning. Avalanche hazard mapping is used by land planning
authorities as tool to prevent buildings being constructed in areas that are endangered by
avalanches. [1]
Advanced methods have been developed to describe several aspects of avalanche hazard
assessment, such as the dynamics of snow avalanches or the intensity of snowfall to assume as a
reference meteorological forcing. [1]
The main objectives of avalanche hazard mapping today are therefore to be seen in the following
fields:
- Digital Terrain Model (DTM) assessment for high quality feature derivation using GIS
- Incorporation of dynamics using animation and simulation techniques
- Perspective three dimensional terrain modeling for advanced topographic comprehension
- Cartographic design, layout and presentation using multimedia technology [3]

3
The major reason of using ArcGIS within avalanche hazard management is to analyse and model
scenarios that can help understand or even predict possible occurrences. In order to do this, it is
important to have large-scale terrain and thematic information. [3]
Several factors influence the avalanche slip, some factors such as snow height and properties,
wind speed and so on, are quickly variable. While others, such as land morphology change
slowly in time. Two kinds of data are used as input: vegetation and morphology. [2]
Due to the fact that in high altitude regions snow cover is persistent for more than six months of
the year, it is becoming important to deal with causes and effects of avalanches. The focal point
is mainly in populated and touristic regions. Monitoring the weather and analysing the resulting
conditions is one important aspect of dealing with potential crucial avalanche situations. On the
other side it is decisive to understand and capture the topographic situation. [3]
According to avalanche experts around the world terrain slope is an important factor in
understanding and predicting potential avalanches with following description in Table 1. [3]
Table 1 - Slope and avalanche probability [3]
Slope Probability of Avalanche
Less than 10o
Practically no avalanches are triggered
10o
– 28o
Avalanches are scarce
28° - 45° Major danger zone for avalanche triggering
above 45° High avalanche frequency, however low snow accumulation due to steepness
Slope cannot exceed 55°, because no snow accumulation would occur, and cannot be lower than
28° since snow slip would be hardly possible. While break lines over the slip areas denote the
presence of convex zone with a slope variation larger than 10°. [2]
In this study according to the literature this model considered to produce the avalanche hazard
map (Figure 1):
- Slope between 28° and 55°
- Slope variation larger than 10° (presence of break lines) [2]

4
Figure 1 - Slope Properties Affecting Avalanche Hazard [2]
Besides, two other effects are considered as aggravating circumstances:
- Mountain aspect:
 S-E aspect: aggravating circumstance during spring
 N aspect: aggravating circumstance during winter
- Wind effect:
 Downwind hazard with respect to the wind prevailing direction (factor
suggested by a mountain guide)
 The wind is more intense in early afternoon, with NE-E prevailing
direction, during the rest of the day the prevailing direction is SW-W

5
Figure 2 - Influence of the wind
The presence of vegetation is not able to stop avalanches once they have started. Nevertheless
vegetation coverage, mainly depending on vegetation density, is able to prevent snow slip and
avalanche occurrence by avoiding the creation of a compact and homogeneous snow layer. All
the available information about vegetation has been processed to form three vegetation classes
with respect to the protection capability against avalanches. [2]
The most important vegetation characteristics for the protection against avalanches are density
and tree type. Therefore, vegetation coverage has been split into three classes:
- Dense evergreen forest (spruce or spruce with larch)
- Sparse wood or deciduous dense wood (larch)
- Bare or covered by grass or sparse vegetation (pasture or bushes) [2]

6
Figure 3 - Influence of the vegetation on the snow layer accumulation [2]

7
2- Project Data
2-1- Site Location
Val di Pejo is located in the north western part of Trentino an Italian alpine region. (Figure 4)
Figure 4- Location of the study area, Val di Pejo (Upper right rectangle)

8
The valley is covered by spruce and larch. Spruce is more present at lower altitudes. The valley
is surrendered by a wide mountain chain and the highest reach is 3700 m. [2]
In the Figure 5 the aerial photo of the project location is presented.
Figure 5 - 2D view of the orthophoto

9
2-2- Available Data
- Forest coverage: comp7 (shapefile, Clascolt field: high forest=1, copse=2, pasture=3, no
data=4)
- Forest coverage: cveg (shapefile, with three classes ("Tipolog" field): Pastures class 3,
Sparse trees wood class 2, Dense forest class 1)
- Aerial photo, to be georeferenced (42010.tif – shape file, contour lines with 10 m
spacing)
- 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.
- Caldes station (46°22′0″N 10°57′0″E): the wind is more intense in early afternoon, with
NE-E prevailing direction, during the rest of the day the prevailing direction is SW-W.
- km024136, km024141, km029136, km029141, km034136, km034141: local base map
- viapri.e00: main roads

10
3- Produced Maps
3-1- DTM
Digital Terrain Model (DTM) is representations of land surface point elevations. They are used
as input for the generation of surface models and contours or the orthorectification process (the
process of removing the effects of image perspective and relief effects for the purpose of creating
a planimetrically correct image) of aerial photography.
The first step is to create a feature class containing points generated from specified vertices of
the input features. Since ArcGIS cannot analysis the contour lines, it is needed to convert all the
contour lines to points. To do so, the Feature Vertices to Points tool in the Data Management
Tools is used. (Figures 6 and 7)
Then it is needed to interpolate a raster surface from the produced points using an Inverse
Distance Weighted (IDW) technique. To do so, the IDW Interpolation tool is used in the Spatial
Analyst Tools.
After generating the DTM map, based on figure 8 it was noticed that some points’ height
coordinates were not relevant with respect to their adjacent points. There were 1000 m
differences in height of some points. These points were corrected in the Attribute Table, and then
the final DTM map was generated according to figure 9.

11
Figure 6- Ortophoto Map without georeferencing (Vertices)
Figure 7 – Points generated from the verttices

12
Figure 8 – DTM map before correction
Figure 9 – DTM map after correction

13
3-2- Morphologic Hazard Map
The main procedure of producing morphologic hazard map has been shown in the following
graph.
DTM Corrected Map Slope Map
Slope Interval Map
(28<a<55)
Break Lines Map
(Slope variation > 10)
Morphologic Hazard Map
(Slope Interval + Break Lines)
3-2-1- Slope Map
First step of producing morphologic hazard map is creating slope map. By using Slope from
Surface tool in Arc Toolbox menu (Figure 10). DTM map should be used as input.
Figure 10 – Slope Map

14
3-2-2- Slope Interval Map
After creating the slope map, it is needed to differentiate between the hazardous slopes and
non-hazardous ones. In avalanche hazard assessments, different intervals have been determined
as hazardous slopes. In our case, slopes between 28° and 55° are considered as the hazardous
slopes, therefore, values between 28° and 55° had to be distinct in order to obtain areas where
avalanches are most likely to slide. This map was produced by using the Raster Calculator tool
in the Spatial Analyst Tools and is shown in figure 11.
Figure 11 –Slope Interval Map

15
3-2-3- Break Lines Map
Another factor which can worsen the hazard level is the presence of break lines. This can be
identified by considering slope variations. Again, in different literatures different slope variations
are determined as the threshold of having break lines. Usually places with slope variations more
than 10° is considered as break lines. By using the tool Block statistics we transformed slope
map into rectangular cells (3x3), then the produced cell map was used as input in order to
produce break lines map of the value greater than 10°, since these are the areas of the avalanche
break line. This map was also created by using the Raster calculator tool. The result is shown in
figure 12.
Figure 12 –Break Lines Map

16
3-2-4-Morphologic Hazard Map
Since the factor of slope is considered as a major cause of avalanche we combine slope interval
between 28° and 55° with the break lines map (slope variation map). For this action, the Raster
calculator tool was used.
The resulting map as is shown in figure 13, morphological hazard map, is used to assess the
avalanche hazard and its related areas. This map permits the identification of different regions
each one characterized by a different feature.
In this map, three levels are defined as following:
0 – No hazard,
1 – Morphologic hazardous area without break lines,
2 – Morphologic hazardous area with break lines.
Figure 13 –Morphologic Hazard Map

17
3-3- Aspect Maps
In Aspect maps DTM was used to graphically display information about the orientation of the
slopes. The aspect helps define the amount of sunlight striking the surface of the terrain, or
consider the seasonal and wind aggravating circumstances. The aspect map can be created using
the Aspect tool in the Spatial Analyst Tools. (Figure 14)
Figure 14 – General Aspect Map
3-3-1- Slope Aspect with respect to the sun
The direction a slope faces with respect to the sun (aspect) has a profound influence on the
snowpack. It often takes several years of experience in avalanche terrain before most people
appreciate the importance of aspect.

18
Based on figure 15, the influence of aspect with respect to the sun is most important at mid
latitudes (Italy locates in this part) from about 30 degrees to around 55 degrees. At equatorial
latitudes, the sun goes almost straight overhead, which shines equally on all slopes. At arctic
latitudes, in the winter, the sun is too low on the horizon to provide much heat and when it
finally gets high enough in the spring and summer, it just goes around in a big circle anyway,
shining on all the aspects with nearly the same intensity. Thus, in the arctic spring, aspect has
some influence but not nearly as significantly as in mid latitudes. Therefore, the importance of
aspect is primarily at mid latitudes.
Figure 15 –Aspect and Latitude in Northern Hemisphere
3-3-2- At mid latitudes in the northern hemisphere
According to figure 16, North facing slopes receive very little heat from the sun in mid-winter.
Conversely, south facing slopes receive much more heat. Therefore, a north facing slopes will
usually develop a dramatically different snowpack than a south facing slope.

19
Figure 16 –North vs. South in Northern Hemisphere
3-3-3- Aggravating Circumstances
There are two other factors that can affect the hazard level: time of the year as different seasons
and wind direction.
As it is given, in spring, the South-East aspect goes under an exacerbation condition. This
happens in the North direction during winter. Aspect extract map for these orientations was
created by using the Reclassify tool. (Figures 17 & 18)
The following procedure was used to create different aggravating conditions from aspect map.
General Aspect Map
Spring Aspect Map
(S-E)
Winter Aspect Map
(N)
Wind Map – Early Afternoon
(SW-W)
Wind Map – Rest of the Day
(NE-E)
DTM Corrected Map

20
Figure 17 –Aggravating Direction in Spring
Figure 18 –Aggravating Direction in Winter

21
Wind effect is variable during the day in such a way that the wind is more intense in the early
afternoon, with Northeast-East prevailing direction, and during the rest of the day the prevailing
direction is Southwest-West.
Since these directions are those of the upcoming winds, their influences are in the opposite
direction. Hence, the aggravating direction in the early afternoon is Southwest-West, and for rest
of the day is Northeast-East. (Figure 19)
Wind aggravation maps have been shown in figures 20 and 21.
Figure 19-Aggravating Direction of wind

22
Figure 20-Aggravating Direction in Early Afternoons
Figure 21-Aggravating Direction in the Rest of the Day

23
3-4- Vegetation Map
Firstly, the provided comp7 map was turned into raster with Feature to raster tool. In order to
produce the vegetation, it was necessary to do the reclassification of the vegetation typology in
the raster. It was reclassified by using the Reclassify tool into five categories:
1 – High forest
2 – Copse
3 – Pasture
4 – No data
5 – No vegetation
Figure 22 shows different vegetation groups for the whole area.
Figure 22 – Map of the Vegetation of Whole Area

24
Then study area should be extracted by using the Clip tool as is shown in figure 23. This gives
possibility to superimpose this map with other maps in the rest of project.
Figure 23 - Vegetation Map (in the case study area)

25
3-5- General Hazard Map
The general hazard map was created by superimposing the morphologic hazard map and the
vegetation map. This was performed with the Raster calculator tool and Reclassify tool for
assessing level of hazard in each area by considering both level of hazard in morphological map
and density of vegetation in those regions. Result is presented in figure 24.
Vegetation Map
(Clip + reclassify comp7)
General Hazard Map
(Morphologic + Vegetation)
Morphologic Hazard Map
(Slope Interval + Break Lines)
Figure 24 – General Hazard Map

26
3-6- Aspect Hazard Map
In this part to account aggravating effects, four different maps for early afternoon and rest of the
day, in winter and spring have been created by using Raster Calculator tool.
In the next steps, these four maps will be presented by overlapping general hazard map. Figures
25 to 28 are representing four different aspect maps.
Aggravating Case 1
(Spring + Early Afternoon)
Aggravating Case 2
(Winter + Early Afternoon)
Aggravating Case 3
(Spring +Rest of the Day)
Aggravating Case 4
(Winter +Rest of the Day)
Final Hazard Map Case 1
(Spring + Early Afternoon)
(Winter + Early Afternoon)
(Spring +Rest of the Day)
(Winter +Rest of the Day)
General Hazard Map
(Morphologic + Vegetation)

27
Figure 25-Aspect Map for Early Afternoon in the Spring
Figure 26-Aspect Map for Early Afternoon in the Winter

28
Figure 27-Aspect Map for Rest of the Day in the Spring
Figure 28-Aspect Map for Rest of the Day in the Winter

29
3-7- Final Hazard Maps and Conclusion
By overlapping Aspect Maps and General Hazard Maps, four different maps have been
concluded. It was noted the avalanche hazard is almost similar in spring and winter since the
dominant factors such as morphological factors and vegetation are common. For those parts with
different hazard levels, main reason is wind direction.
Based on the obtained results, it is clear that avalanche hazard level is higher in early afternoon
spring and early afternoon winter than rest of the day spring and rest of the day winter.
In addition, but to some extent, the early afternoon spring avalanche hazard map shows higher
hazard levels generally speaking.
In addition, all final hazard maps are compared with the map of possible avalanche location
(CLPV, Carta di Localizzazione Probabile delle Valanghe), which is based on past events.
(Figures 29 to 32).
As it can be seen, the results of the spring and winter hazard maps are in accordance with the
occurred avalanche map.
This is in agreement with common sense, since on the one hand the level of hazard is higher in
spring and winter due to the more rate of snowing, on the other hand the occurred avalanche
areas map is most probably produced in the most hazardous time of the year.

30
Figure 29-Hazard Map for Rest of the Day in the Spring

31
Figure 30-Hazard Map for Rest of the Day in the Winter

32
Figure 31-Hazard Map for Early Afternoon in the Winter

33
`
Figure 32-Hazard Map for Early Afternoon in the Spring

34
4- Georeferencing
Georeferencing means to associate something with locations in physical space. The term is
commonly used in the geographic information systems field to describe the process of
associating a physical map or raster image of a map with spatial locations. Georeferencing may
be applied to any kind of object or structure that can be related to a geographical location, such
as points of interest, roads, places, bridges, or buildings. Geographic locations are most
commonly represented using a coordinate reference system, which in turn can be related to a
geodetic reference system. [4]
In this part georeferencing of the aerial photo (42010.tif – shape file, contour lines with 10 m
spacing) is presented.
In order to do this “Monte Mario Italy 1” was selected for the reference system and then using
Georeferencing option and by selecting 4 common points in the orthophoto and local base maps
the transformation was carried out.
Then using ArcScence and adding the georeferenced orthophoto and also the final DTM
database, the 3D map of the area has been created. (Figure 33)
Finally, four different hazard maps have been added to the 3D map to create a 3D view of
hazardous areas.
Figures 34 to 37 show the 3D Hazard map in different aggravating conditions.
Also it is clear that the hazard is generally highest in the eastern part of the region with higher
altitudes, steeper slopes and high mountain peaks.

35
Figure 33 – 3D Map generated by ArcScene

36
Figure 34 – 3D Hazard Map for Early Afternoon in the Spring
(Circles show the most hazardous areas)
Figure 35 – 3D Hazard Map for Early Afternoon in the Winter

37
Figure 36 – 3D Hazard Map Rest of the Day in the Spring
Figure 37 – 3D Hazard Map Rest of the Day in the Winter

38
5- References
1. Pistocchi A., Notarnicola C., “Data-driven mapping of avalanche release areas: a case
study in South Tyrol, Italy”, Nat Hazards, 2013, 65:1313–1330.
2. Ciolli M., Zatelli P. (2000), Avalanche risk management using GRASS GIS, 1st Italian
GRASS users meeting proceedings, Geomatics Workbooks, Vol. 1,
3. K. KRIZ, “Using GIS and 3D Modeling for Avalanche Hazard Mapping”, Proceedings of
the 20th ICA, Beijing, China, 2013.
4. Wikipedia (http://en.wikipedia.org/wiki/Georeference)

Development of avalanche hazard maps by ArcGIS for Trentino (Alpine Italy)

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