|
TOPOGRAPHY
The
mountains terrain of Sikkim consist of a tangled series of interlacing
ridges, rising one above the other, from south to the foot of the high
peaks, which mark the abode of snow in the North. The total area can
be divided into nine (9) unequal parts as follows:
1. Summits
and ridges
2.
Escarpments
3. Very
steep slopes (>50%)
4. Steep
slopes (>30-50%)
5.
Moderately steep slopes (15-30%)
6. Narrow
valleys (<30%)
7. Cliffs
and precipitous slopes
8. Zones of
glacial drifts/marine/boulders.
9. Perpetual
snow
Considering the degree of slopes, vegetation and geology, the above
can be further regrouped into five broad physiographic divisions.
summits and
ridges, side slopes of hills, valleys, rock cliffs and, glacial zone
CLIMATE
The climate of the State has been roughly divided into the
Sub-Tropical, Temperate and Alpine zones. For most of the year, the
Climate is cold and humid and rainfall occurs in each month. The area
experiences heavy rainfall due to its proximity to the Bay of Bengal.
The rainfall in South District is comparatively less than in other
Districts. The general trend of decrease in temperature with in
increase in altitude holds good everywhere. Pre-monsoon rain occurs in
April- May and Monsoon (South-West) operates normally from the month
of May continuing up to early October.
TEMPERATURE
The mean
temperature in the lower altitudinal zones varies between 4.5º
C to 19.5º C whereas at
higher altitudinal zones it varies from 1,5º
C to 9.5º C.
Temperature varies with altitude and slope. The maximum temperature is
recorded usually during July-August and minimum during
December-January. Fog is a common feature in the month of May to
September. Biting cold is experienced at high altitude places in the
winter months and snowfall is also not uncommon during this period.
RAINFALL
An
examination of available rainfall data shows that the mean annual
rainfall is minimum at Thangu (82mm) in North Sikkim and maximum at
Gangtok (3494 mm) in east Sikkim. An isohyetal analysis of this data
reveals that there are two maximum rainfall areas (i) South-East
quadrant, including Mangan, Singhik, Dikchu, Gangtok and Rongli (ii)
South-west quadant, including hilly. In between these two regions,
there is a low rainfall region (e.g., Namchi), Rainfall in this area
is about half of that in the former areas. There is an area in
northwest Sikkim which gets little rainfall (even less than 4.9mm).
This area is mainly snow-covered mountains, Rainfall is heavy and well
distributed during the months of May to early October. July is the
wettest month in most places. The intensity of rainfall during
southwest monsoon season decreases from South to north, while the
distribution of winter rainfall is in the opposite order. The highest
annual rainfall for individual stations may exceed 5000mm. and average
number of rainy days (days with rain of 2.5 mm or more) range from 100
at Thangu to 185 at Gangtok. |
