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Nepal Hazard Risk Assessment
H r = (S r x Six S h x S v )xT p (1)
H e = (Sr X Si X Sh X Sv) x T s (2)
Where Hr and He are landslide hazard indices for rainfall and earthquake induced landslides respectively,
Sr is the slope factor within a selected grid, Sl is lithological (or geological) conditions factor, S h
describes the soil moisture condition, T p is the precipitation factor and T s describes the seismic
conditions. The index Sv described the vegetation cover.
3.3.5 HOW TO READ THE MAPS
Both classes of landslide hazard maps contain 4 categorized zones as negligible, low, medium, and high.
The legend shown in maps is indicating color and respective hazard zoning.
Negligible –Very low probability of landsldies
Low - Low probability of landsldies
Medium – Medium probability of landsldies
High –High probability of landsldies
The Table 3.6 and Table 3.7 show percentage area distribution of landslide zone within each district.
These maps are presented for country scale. Slightly more detail information can be referred for district
level, especially for the dominant landslides classes.
3.3.6 ANALYSIS OF HAZARD ASSESSMENT
Slope, lithology, soil moisture, and precipitation are controlling factors for landslide hazard, while
earthquake and rainfall are triggering factors. Peak of monsoon usually correlate with high landslide
events in Nepal due to high precipitation. Data on the importance of earthquake triggered vs
precipitation triggered in terms of fatalities may not be easily available. It is known that in some cases, a
significant share of the earthquake fatalities are killed by earthquake triggered landslides.
High susceptibility zone of landslide due to earthquake hazard are distributed in centre (hill) zone of
Nepal, which is largely dependent on PGA values. Medium severity zone situated surrounding high
severity zone and cover smaller percentage of geographical area. Negligible and low zone areas are
located in north and southern border of Nepal. Figure 3.14 provides insight of area covered under
earthquake induced landslide in the country. As per the assessment, for 500 years return period induced
landslides, two third of the areas of Myagdi, Ramechhap, Parbat, Jajarkot, Kalikot, Okhaldhunga,
Rukum and Baglung will be in high landslide susceptible zone. Similarly more than one third of the
Solukhumbu, Sankhuasabha, Dolakha, Khotang, Accham, Sindhupalchowk, Bhaktapur, Baitadi, Rolpa,
Sindhuli, Lamjung, Dailekh, Syangja, Kabhrepalanchok, Bajura, Nuwakot, Dhading, Tanahu, Kaski,
Bajhang and Darchula will be affected. Figure 3.12 shows medium and high zones are clustered to low
percentage area. Conversely negligible zone is clustered toward maximum (100%) zone.
Figure 3.12. Hazard vs total area cross plot for earthquake triggered landslide.
The rainfall induced landslide zones are distributed relatively normal (normal distribution) with large
area having low and medium severity. High severity zone areas are relatively governed by specific
lithology condition and slope degree. Based on analysis, more than 20 % of geographical areas of
Rukum, Arghakhanchi, Baglung, Ilam, Tanahu, Syangja, Mustang and Palpa are prone to high landslides
triggered by high intensity rainfall. More than 10 % of Jajarkot, Rasuwa, Salyan, Baitadi, Terhathum,
Surkhet, Bajhang, Bajura, Rolpa, Darchula, Pyuthan, Gulmi, Dolpa, Nawalparasi and Panchthar are
prone to high landslide under above stated category. Figure 3.13 shows low and medium hazard zones
are distributed evenly within overall districts. High hazard value is clustered in low percentage hazard
zone area. Conversely low zone is clustered in maximum percentage zone.
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