Some of the most common and frequent natural hazards that occur in Nepal are:
Landslides:
Among
the natural hazards that occur regularly in Nepal, floods and landslides are by far the most serious ones. They claim many
human lives every year and cause other damages such as destruction and blockages of highways, losses of livestock, crops,
and agricultural land. Based on a reconnaissance study, Laban (1979) estimated that at least 75 percent of all landslides
in Nepal were natural. Brundsen et al. (1981), working in the Middle Mountains of Nepal, conclude that landslides should be
considered normal rather than exceptional in the study area.
Earthquakes:
Geologically,
Nepal is considered to lie on a seismic zone which experiences frequent earthquakes. As a result, earthquakes of various magnitudes
occur almost every year and have caused heavy losses of lives on several occasions. Based on the data available from the Department
of Mines and Geology, CBS (1998) concludes that earthquakes of more than or equal to 5.0 on the Richter scale have occurred
at least once every year in Nepal since 1987, with the exception of 1989 and 1992 when no such events were recorded.
Scientists attribute the occurrence of frequent earthquakes
in Nepal to the disturbances occurring due to the continuous encroachment of the Indian subcontinental plate into the main
Asian plate. At the same time, two major parallel fault systems called the Main Boundary Thrust (MBT) and Central Boundary
Thrust (CBT) cross Nepal longitudinally. Constant adjustments and readjustments taking place in these fault systems are known
to trigger earthquakes in the country as well.
Windstorms, hailstorms,
thunderbolts:
Windstorms, hailstorms and thunderbolts (lightening strikes) also occur frequently in
Nepal and affect many areas of the country on a regular basis. Although not as serious as floods, landslides, and earthquakes
these events, nevertheless, cause loss of human lives and damages to properties. Analyzing the available data (DPTC, 1997),
CBS (1998) concludes that in 1995, forty-five districts of Nepal were affected by hailstorms, windstorms and thunderbolts.
These events, particularly the hailstorms, cause considerable damages to the standing crops in the fields.
Forest Fire
Every
year forest fires occur in many places of the country and cause heavy loss of property as well as loss of many species of
wildlife. Nepal has no statistics on the occurrence of forest fires, and no assessment of impact on the economy or on the
environment of the country is available. Though there are no records, forest fire is mainly caused by ignorance and illiteracy
of local people, or personal interest such as interest of illegal wood cutters, poachers, charcoal traders, or persons encroaching
on forest land. There is no record of forest fires caused by natural events like thunderbolts. About 45 percent of forest
fires with known causes are due to burning for new grass to graze cattle and to smokers. About 64 percent of forest fires
are set intentionally by local people. The share of accidental cause of forest fire is only 32 percent. The Department of
Forest is the main responsible government organization to control forest fire. But progress on this field is yet to be achieved
due because of lack of resources, lack of specific fire control rules and regulations, etc.
Source: CBS, 1998
Glacial lake outburst
flood events:
Apart from landslides and river erosion, the high mountains or Himalayas of Nepal, covering
about 15 prcent of the country, are quite susceptible to land degradation caused by glacial lake outburst floods (GLOF). These
mountains, with an average elevation of 4 500 m. on, are mostly covered with snow and ice throughout the year. Since the second
half of the twentieth century, the large glaciers of the high mountains have been experiencing rapid melting, resulting in
the formation of a large number of glacial lakes. This may well be a result of global warming. Almost all the glacial lakes
of the Himalayas are formed by a glacier terminus dammed by moraine. These moraine dams are not geologically consolidated
enough and a slight disturbance can break the balance of the structure, resulting in an abrupt release of a great amount of
water and generating floods. These floods can cause serious damage to infrastructure, houses, and the environment along the
flood path downstream. This phenomenon is called a glacial lake outburst flood (GLOF).
In Nepal, GLOF events have been occurring for many decades,
but this catastrophic glacier phenomenon came into the limelight only after 1985, when the Dig Tsho glacier outburst took
place. Investigations into the nature of glacial lakes began in the country. In 1996, the Water and Energy Commission Secretariat
(WECS) of Nepal reported that five lakes were potentially dangerous, namely, Dig Tsho, Imja, Lower Barun, Tsho Rolpa, and
Thulagi, all lying above 4100m. Their extent ranges from 0.6 to 1.39 sq. km. The maximum depth ranges from 81 to 131m, with
ages above 30 years. A recent study done by ICIMOD and UNEP (UNEP, 2001) reported 27 potentially dangerous lakes in Nepal.
In ten of them GLOF events have occurred in the past few years and some have been regenerating after the event. This means
activities have to be planned carefully in order to avoid human-instigated triggering factors creating an outburst. A monitoring
system for lakes with outburst risk should be established to avoid flood hazards.
Source: UNEP, 2001
