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Nepal Hazard Risk Assessment
3.3 LANDSLIDE HAZARD ASSESSMENT
Landslide hazard is frequent phenomenon is Nepal due to several reasons including tectonic activities,
uncontrolled and unsafe development, heavy precipitation and environmental degradation. However it is
observed that rainfall induced landslides is most prevalent in the hills and mountainous districts. In view
of rapid development in hills and mountains in the country, it has become imperative to review, identify
and analyze landslide prone areas and their causative factors. The present landslide hazard assessment
carries out the hazard zonation of the country based on two triggering factors like earthquake and heavy
precipitation.
3.3.1 MAP CONTENT
Landslide hazard maps show two classes of landslide zoning caused by earthquake events and heavy
rainfall. The maps further show landslide hazard severity distribution in all districts triggered by above
stated factors.
3.3.2 APPLICATION OF MAPS IN DISASTER RISK MANAGEMENT
• Two types of maps show the severity of landslide caused by rainfall and seismic events. The
maps will help the planning and development agencies for physical and social development in
hazard prone areas.
• The maps will be especially helpful to Ministry of Physical Planning and Works, Ministry of
Information and Communication, Ministry of Irrigation, Department of Electricity Development,
Department of Road for sectoral development in landslide prone districts and region.
• The study reveals that road sector is most prone to landslides during monsoon season. The
Department of Road has initiated several structural mitigation projects at local level. The maps
will help in identifying the sites for structural and non structural mitigation projects. The maps
will help in prioritizing the site specific studies and mitigation interventions.
• DWIDP closely monitors water induced disaster activities. The maps will help the department to
focus on landslide disaster prone areas and seek cooperation with various other response agencies
and departments for better disaster preparedness.
• Precipitation data from Global Precipitation Climatology Centre (GPCC) that can be assessed in
http://gpcc.dwd.de
• Land cover database from European Space Agency (ESA) that can be assessed in
http://www.esa.int/esaEO/SEMGSY2IU7E_index_0.html
• Seismic Trigger Factor from PGA by NGI (NGI, 2004)
The details of data may be referred at reference section of the report.
3.3.4 METHODOLOGY
The present methodology has been derived from NGI based on landslide hazard assessment, which can
be referred in detail in Annexure-2.
Landslide hazard, defined as the annual probability of occurrence of a potentially destructive landslide
event, was estimated by an appropriate combination of the triggering factors (mainly extreme
precipitation and seismicity) and susceptibility factors (slope, lithology, and soil moisture). The
methodology is presented in Figure 3.11. The weights of different triggering and susceptibility factors
were calibrated to the information available in landslide inventories and physical processes. The general
approach used in the present study is a modified and improved version of the approach used by Nadim et
al. (2006).
3.3.3 DATA AVAILABILITY FROM SOURCES
Data source for producing the maps are:
• Elevation data (SRTM) from Isciences, which can be assessed in
http://www.isciences.com/index.html
• Lithology from Nepal Department of Mines and Geology (DMG, 1987) on 1:250.000 scale maps
• Moisture index data from Climate Prediction Center (CPC), which can be assessed in
http://iridl.ldeo.columbia.edu/SOURCES/.NOAA/.NCEP/.CPC/.GMSM/
Figure 3.11. Schematic approach for landslide hazard and risk evaluation.
The hazard maps are divided into precipitation induced landslide hazard and earthquake induced
landslide hazard. The landslide hazard indices were estimated using the following equations:
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