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Nepal Hazard Risk Assessment
Extreme Did not exist
before 1999.
2006 is a worst
winter drought
year
(b) Drought occurrence probability
More common
since 1990's, but
reported in less
number of
stations recently
Lull period
during 1990's.
Occur in few
places
Rare and reported in only
few places. Has not
occurred since 2001.
The average probabilities of occurrence of moderate, severe and extreme droughts have been computed
and depict the climatological (1977-2007) and decadal probabilities for the four seasons (Tables 2, 3 and
4).
The Table 3.2 depicts the climatological (1977-2007) and decadal probability of occurrence of moderate
drought for the four seasons. Climatologically, monsoon shows less probability (3.2%) and premonsoon
shows high probability (8.3%) of experiencing moderate drought. In both of these seasons including
postmonsoon season, during 1988-1997, the probability of drought occurrence increased, but decreased
again during 1998-2007. However winter drought showed a slight decrease during 1988-1997 but the
probability increased (10.3%) in the recent decade (1998-2007). This indicates that chances of occurring
droughts in winter are increasing and are more than the other seasons. So there is need to promote
drought tolerant verities and prioritize research in development of drought resistance varieties especially
for winter crops. Emerging threats to food security also demand the need of building irrigation
infrastructure in highly productive but drought susceptible areas.
Table 3.2: Moderate drought occurrence probability (%)
Winter Premonsoon Monsoon Postmonsoon
Climatology 7.7 8.3 3.2 6.5
1977-1987 6.4 8.9 8.2 6.4
1988-1997 6.1 9.3 10.9 13.2
1998-2007 10.3 5.2 4.6 5.4
Table 3.3 depicts the climatological (1977-2007) and decadal probability of occurrence of severe
droughts for the four seasons. Climatologically, monsoon shows less probability of occurrence (3.8%)
and winter shows comparatively high probability (5.3%) of experiencing severe drought. In monsoon the
probability decreased during 1988-1997 but increased slightly during 1998-2007. During premonsoon
and postmonsoon seasons the probability increased during the 1988-1997 decade but then decreased
again significantly during 1998-2007. However winter drought showed no change in average probability
during 1988-1997 but the probability remarkably increased (11.3%) in the recent decade (1998-2007).
This indicates that chances of occurring severe droughts in winter have increased significantly and are
also more than in the other seasons.
Table 3.3: Severe drought Occurrence probability (%)
Winter Premonsoon Monsoon Postmonsoon
Climatology 5.3 4.2 3.8 3.9
1977-1987 2.3 4.2 4.6 1.6
1988-1997 2.3 6.7 3 7.5
1998-2007 11.3 1.7 3.6 2.8
Table 3.4 depicts the climatological (1977-2007) and decadal probability of occurrence of extreme
drought for the four seasons. Climatologically, postmonsoon shows less probability (3.8%) and pre and
post monsoon show comparatively high probability (3.5%) of experiencing extreme drought. In
monsoon the probability decreased during 1988-1997 but increased again during 1998-2007. During
premonsoon and postmonsoon seasons the probability increased during the 1988-1997 decade but then
decreased again during 1998-2007. However winter drought showed increase in probability of
occurrence during 1988-1997 (0.5%) and significantly (7.6%) in the recent decade (1998-2007). This
indicates that chances of occurring extreme droughts in winter have increased significantly and are also
higher than in the other seasons.
Table 3.4: Extreme drought occurrence probability (%)
Winter Premonsoon Monsoon Postmonsoon
Climatology 2.8 3.5 3.5 0.9
1977-1987 0.4 2.8 5.5 0.7
1988-1997 0.5 5.7 0.8 1.3
1998-2007 7.6 2.2 4.1 0.8
The probability of occurrence of moderate to extreme droughts was also computed (Table 3.5). The table
depicts the climatological and decadal probability for all the seasons. Climatologically, postmonsoon
shows less probability (13.6%) and premonsoon shows most probability (15.9%) of experiencing
drought in Nepal. In both of these seasons, during 1988-1997, the probability of drought occurrence
increased suddenly, but decreased significantly again during 1998-2007. The monsoon season shows the
decrease in the probability in later decades. Winter season however shows a large increase in the
probability (28.7%) in the recent decade (1998-2007). This indicates that chances of occurring droughts
in winter are more than in the other seasons.
Table 3.5: Probability of occurrence of moderate to extreme drought (%)
Winter Premonsoon Monsoon Postmonsoon
Climatology 15.3 15.9 15.5 13.6
1977-1987 8.7 15.9 18.1 8.7
1988-1997 8.4 21.4 14.7 22.0
1998-2007 28.7 10.6 13.7 10.4
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