|
NepalClimate
Nepal has a great deal of variation in climate. Its
latitude is
about the same as that of Florida, and a tropical and
subtropical
climate exists in the Tarai Region. Outside the Tarai,
however, the
climate is completely different. The remarkable
differences in
climatic conditions are primarily related to the enormous
range of
altitude within such a short north-south distance. The
presence of
the east-west-trending Himalayan massifs to the north and
the
monsoonal alteration of wet and dry seasons also greatly
contribute
to local variations in climate. Scholar Sharad Singh Negi
identifies five climatic zones in Nepal based on altitude:
the
tropical and subtropical zone of below 1,200 meters in
altitude;
the cool, temperate zone of 1,200 to 2,400 meters in
altitude; the
cold zone of 2,400 to 3,600 meters in altitude; the
subarctic
climatic zone of 3,600 to 4,400 meters in altitude; and
the arctic
zone above 4,400 meters in altitude. In terms of natural
vegetational regimes or distribution patterns, altitude
again plays
a significant role. Below 1,200 meters, the dominant form
of
vegetation consists of tropical and subtropical rain
forests.
Altitude also affects annual rainfall or precipitation
patterns. Up to about 3,000 meters, annual rainfall totals
increase
as the altitude increases; thereafter, annual totals
diminish with
increasing altitude and latitude. In addition to this
latitudinal
differentiation in rainfall, two other patterns can be
discerned.
First, given the northwestward movement of the
moisture-laden
summer monsoon (June to September), the amount of annual
rainfall
generally decreases from east to west. However, there are
certain
pockets with heavy annual rainfall totals, for example,
the Pokhara
Valley in central Nepal. Second, the horizontal extension
of hill
and mountain ranges creates a moist condition on southand eastfacing slopes whereas it produces a major rain shadow on
the
northern sides of the slopes. The aridity increases with
altitude
and latitude, especially on the northern slopes, and
reaches its
climax in the inner Himalayan region and on the Tibetan
Plateau.
Eastern Nepal receives approximately 2,500 millimeters of
rain
annually, the Kathmandu area about 1,420 millimeters, and
western
Nepal about 1,000 millimeters.
The towering Himalayas play a critical role, blocking
the
northwesterly advances of moist, tropical air from the Bay
of
Bengal, and ultimately leading to its conversion to rain
in the
summer. In the winter, this range prevents the outbursts
of cold
air from Inner Asia from reaching southern Nepal and
northern
India, thus ensuring warmer winters in these regions than
otherwise
would be the case.
In addition, there are seasonal variations in the
amount of
rainfall, depending on the monsoon cycle. Bishop divides
the
monsoon cycle into four seasons: premonsoon, summer
monsoon,
postmonsoon, and winter monsoon. The premonsoon season
generally
occurs during April and May; it is characterized by the
highest
temperatures, reaching 40° C during the day in the Tarai
Region and
other lowlands. The hills and mountains, however, remain
cool.
The summer monsoon, a strong flow of moist air from the
southwest, follows the premonsoon season. For the vast
majority of
southern Asians, including Nepalese, the term
monsoon is
synonymous with the summer rainy season, which makes or
breaks the
lives of hundreds of millions of farmers on the
subcontinent. Even
though the arrival of the summer monsoon can vary by as
much as a
month, in Nepal it generally arrives in early June, is
preceded by
violent lightning and thunderstorms, and lasts through
September,
when it begins to recede. The plains and lower Himalayas
receive
more than 70 percent of their annual precipitation during
the
summer monsoon. The amount of summer monsoon rain
generally
declines from southeast to northwest as the maritime wedge
of air
gradually becomes thinner and dryer. Although the success
of
farming is almost totally dependent on the timely arrival
of the
summer monsoon, it periodically causes such problems as
landslides;
subsequent losses of human lives, farmlands, and other
properties
(not to mention great difficulty in the movement of goods
and
people); and heavy flooding in the plains. Conversely,
when
prolonged breaks in the summer monsoon occur, severe
drought and
famine often result.
The postmonsoon season begins with a slow withdrawal of
the
monsoon. This retreat leads to an almost complete
disappearance of
moist air by mid-October, thus ushering in generally cool,
clear,
and dry weather, as well as the most relaxed and jovial
period in
Nepal. By this time, the harvest is completed and people
are in a
festive mood. The two biggest and most important Hindu
festivals--
Dashain and Tihar (Dipawali)--arrive during this period,
about one
month apart
(see Religion
, this ch.). The postmonsoon
season lasts
until about December.
After the postmonsoon, comes the winter monsoon, a
strong
northeasterly flow, which is marked by occasional, short
rainfalls
in the lowlands and plains and snowfalls in the
high-altitude
areas. The amount of precipitation resulting from the
northeast
land trade winds varies considerably but increases
markedly with
elevation. The secondary winter precipitation in the form
of
snowfalls in the Himalayas is important for generating a
sufficient
volume of spring and summer meltwaters, which are critical
for
irrigation in the lower hills and valleys where
agriculture
predominates. Winter precipitation is also are
indispensable for
the success of winter crops, such as wheat, barley, and
numerous
vegetables.
Data as of September 1991
|
