 |
 Climate
The region has a humid, tropical, maritime
climate with an annual rainfall of about 1,650-1,860 mm in
central & northern areas, and as much as 2,790 mm on the
outer coast. The mean annual rainfall recorded at the observatory
of the Island of Sagar was 2002mm in 1937-1946, that for Jhingakhali
Station in the northern part of the reserved forests was 1920mm
in 1970-1972. Rainfall is heavy and humidity high (80% on
average) due to the proximity of the Bay of Bengal. The monsoon
starts in July and usually continues until October, with occasional
rains throughout the year. The winter months of January and
February have low temperature & low precipitation. The
mean maximum temperature is 290C(June-July) and the mean minimum
temperature is 200C(December-January). From October to mid-March,
the prevailing winds are from the northeast, while during
the monsoon season, they are from the southwest. Violent south-westerlies
prevail from mid-March to September. Storms are common in
May and October-November, sometimes developing into cyclones,
which are usually accompanied by tidal waves and cause much
loss of life and damage to property and the forests (Lahiri,
1973).
The coastal zone of West Bengal experience
a moderate type of climate because of its location adjacent
to the Bay of Bengal as well as due to regular tidal flushing
in the estuaries. Wave actions, micro and macro tidal cycles,
long shore currents are recorded in most of the islands of
the ecosystem. Coastal processes are very dynamic and are
accelerated by tropical cyclones which is locally called 'Kal
Baisakhi' (Nor' Wester).
The seasonal climate may be conveniently
categorized into pre-monsoon (March-June), monsoon (July-October)
and post-monsoon (November-February). Each season has a characteristic
feature of its own, which is very distinct and unique.
1.) Wind
The direction and velocity of the wind system are mainly
controlled by the northeast and southwest monsoons. The wind
from the north and northeast commences at the beginning of
October and continues till the end of March.
The month of January and February are relatively calm with
an average wind speed around 3.5 Km/hour. Violent wind speed
recommences from the southwest around the middle of March
and continues till September. During this period, several
lower pressure system occur in this region, a number of which
takes the form of depressions and cyclonic storms of varying
intensity.
2.) Waves and Tides
The Wind is the basic driving force for generating surface
waves in the coastal zone of West Bengal . Sea waves in this
region rarely become destructive except during cyclonic storms.
During Nor-westers, the wind speed rises above 100 Km/hour
and is usually accompanied by huge tidal waves. When the cyclonic
incidences coincide with the spring tides, wave height can
rise over 5 m above the mean sea level. Ripple waves appear
in the month of October, November and December when wind generated
wave height varies approximately from 0.20 to 0.35 m. In the
month of April to August, large wavelets are formed in the
shelf region and they start breaking when they approach towards
the coastal margin. Wave height rises up to 2 m during this
period, which causes maximum scouring of landmasses. Wave
actions, micro-tidal cycles and long shore currents are recorded
in most of the islands in this ecosystem.
With the change in season, tidal pattern in the estuarine
system of coastal West Bengal also changes (Pillay, 1958).
During the monsoon month, the effect of flood tide is more
or less countered and nullified by freshets and there is a
strong predominance of ebb tide. The strength of flood tide
over ebb tide is at a minimum during the post-monsoon season.
Conversely, during the pre-monsoon season, the effect of flood
tide is considerably stronger than that of the ebb tide.
3.) Rainfall
Rain fall is usually maximum during the month of August
/ September and the monsoon period last from July to October.
The southwest wind triggers the precipitation in the monsoon
period with an average rainfall of about 165 mm (Mitra, 1994).
The postmonsoon period (November to February) is characterized
by negligible rainfall and the premonsoon period (March to
June) is basically dry, but occasionally accompanied by rains
and thunderstorms.
|
Cyclonic
Storm in West Bengal, which crossed the Sundarbans Coast
during the period ( 1907 - 1997 )
|
|
Year
|
Duration
of Storm
|
Maximum
Wind Speed (Km/hr)
|
|
1907
|
17th
- 19th June
|
95
|
|
1907
|
24th
& 25th June
|
95
|
|
1909
|
17th
& 18Th October
|
126
|
|
1912
|
5th
& 6Th September
|
81
|
|
1913
|
23rd
- 25th July
|
126
|
|
1916
|
21st
& 22nd September
|
68
|
|
1916
|
9th
& 10th November
|
81
|
|
1917
|
3rd
May
|
126
|
|
1917
|
30th
& 31st October
|
45
|
|
1919
|
24th
& 25th September
|
126
|
|
1920
|
21st
- 23rd July
|
81
|
|
1921
|
26th
& 27th July
|
68
|
|
1925
|
27th
& 28th June
|
81
|
|
1927
|
28th
& 29th July
|
126
|
|
1928
|
18th
- 20th July
|
126
|
|
1929
|
15th
- 17th July
|
56
|
|
1932
|
23rd
& 24th May
|
126
|
|
1933
|
20th
& 21st September
|
56
|
|
1935
|
8th
& 9th July
|
126
|
|
1936
|
26th
& 28th May
|
113
|
|
1937
|
28th
& 29th September
|
126
|
|
1940
|
30th
June & 1st July
|
-
|
|
1940
|
7th
& 8th July
|
-
|
|
1940
|
2nd
& 3rd August
|
-
|
|
1940
|
21st
& 22nd October
|
-
|
|
1941
|
9th
& 10th July
|
81
|
|
1941
|
8th
& 9th August
|
-
|
|
1942
|
9th
& 10th July
|
81
|
|
1945
|
1st
& 2nd July
|
81
|
|
1946
|
4th
& 5th October
|
81
|
|
1950
|
10th
& 11th June
|
95
|
|
1950
|
10th
& 11th June
|
87
|
|
1952
|
4th
July
|
-
|
|
1956
|
30th
May - 2nd June
|
-
|
|
1960
|
27th
- 29th May
|
74
|
|
1960
|
27th
- 29th May
|
76
|
|
1962
|
20th
& 21st September
|
93
|
|
1962
|
20th
& 21st September
|
80
|
|
1965
|
10th
& 11th May
|
74
|
|
1997
|
20th
& 21st August
|
120
|
|
