Cloud amount: Cloud is a visible body of very fine water droplets or ice particles suspended in the atmosphere at altitudes ranging up to several miles above sea level. The unit of measurement is 'okta'.
Distance from the sea: Presence of sea affects the climate of a place as moderating effects are seen. Coastal areas are cooler and wetter than inland areas.
Ocean current: The directed movement of ocean water that flows in a specific direction. The currents are generated from the forces acting upon the water like the earth's rotation, the wind, the temperature and salinity differences and the gravitation of the moon.
The direction of prevailing winds: Winds that blow from the sea often bring rain to the coast and dry weather to inland areas.
Relief: Mountain relief affects climate immensely as they receive more rainfall than low lying areas. As the altitude increases, there is a decrease in temperature because air becomes thinner and does not retain heat.
Proximity to the equator: Places lying in the equatorial belt receives more sunlight than the anywhere else on earth.
Human Influence - Apart from natural factors, climate also gets affected by anthropogenic activities. With the industrial revolution, there is a significant rise in carbon dioxide in the atmosphere leading to global warming.
Significant climatic variations are seen in West Bengal, and these are due to the topography and the geographical location. The Northern Bengal remains cool throughout the year due to the presence of Eastern Himalayas whereas the influence of sea enables Southern Bengal to experience modern climate.
The factors mentioned above enable West Bengal to experience varied climate from tropical Savannah in southern portions to the humid subtropical in the North. Overall the State experiences a tropical monsoon type of climate. The mountainous terrain and eastern plains get plenty of rainfall whereas the western plateau is comparatively dry.
There are five main seasons in West Bengal- spring, summer, rainy season, short autumn and winter.
- Summer season
During this season, the whole of West Bengal receives vertical rays of the Sun, and the landmass gets heated. This season covers the period between March to mid-June (May is the hottest month of this season) and temperature ranges from 35°-45°C.
- The western part of the State records high temperature than the eastern part as the later observes moderating effect of the sea. The highest temperature of 45°C is recorded in Asansol city of West Bengal.
- Overall the summers are pleasant with an average temperature between 15-20°C.
- During night cool southerly breeze blows carrying moisture from the Bay of Bengal.
Note: Hot summer months observe thunderstorms called Nor-westers or Kal Baisakhi in West Bengal. It generally occurs due to cyclones originating in the Bay of Bengal. These stormy winds are considered suitable for paddy and jute crops.
2. Rainy Season
The South-West Monsoon leads to the rainy season in the State. The intense heat in Northern India develops a low-pressure system which attracts rain-bearing winds from the sea.
- By mid-June, the whole of the West Bengal comes under the influence of South-West monsoon, and the heavy rain shower prevails till September.
- Highest rainfall inWest Bengal is recorded at the foothills of the Himalayas -Darjeeling, Coochbehar and Jalpaiguri districts get the most torrential rainfall in the State (i.e. about 200-400 cm).
- Though the coasts and mountainous terrain receive good rainfall, the Western plateau area, i.e. Bankura and Purulia are comparatively drier with 100-150 cm of rain.
Note: Buxa Duar in Jalpaiguri receives the highest rainfall in the State while Mayureswar in Birbhum receives the lowest rainfall.
3. Autumn/Retreat Monsoon Season
After September the South-West monsoon winds start moving back towards the sea, this is called the retreating of the monsoon winds. The retreat of South-West monsoon over West Bengal is complete by the end of November. This results in tropical cyclones which affect the South and the South-Western part of the State causing heavy rain. These cyclones are known as 'Ashwiner Jhar' as it mostly takes place during the Ashwin (autumn) season.
4. Cold Weather Season
Winter season prevail in the State from mid-November to till mid-February (lasts about three months). January is the coldest month of the State. During this season humidity is very low as the offshore winds blow over the State are devoid of moisture. The offshore winds are part of north-East trade winds and blow over the West Bengal state in the months December to February.
- Winter is mild over the plains, the average minimum temperature not falling 15 degrees C.
- In winters rabi crops such as pulses, potato and vegetables also citrus fruits grow well in Darjeeling hills.
- The cold is severe on the hills, and there are sometimes sleet and snow on the higher reaches during the days of rain.
- The temperature over the Western plateau areas drops considerably, but this region does not become as cold as the mountainous districts in the North.
5. Spring Season
This season is the most pleasant season over the plains of West Bengal and lies from mid-February to mid-March. Temperature range is between 20-30°C and no rainfall. Though occasional rain or light showers witnessed due to Western disturbances in North India.
Let us know about the climate of some prominent cities of West Bengal.
Kolkata has much less rainfall in winters than in summer. Overall with an annual rainfall of 1735mm, Kolkata witnesses tropical climate. The temperature of the city averages 26.2 °C.
With an average rainfall of 1298 mm, the city observes tropical climate and summers are comparatively rainier than the winters. The average temperature here is 26.5 °C.
The tropical climate is observed in Krishnanagar with an average rainfall of 1353 mm, and the average annual temperature is 26.4 °C.
The tropical climate is observed in Nabadwip and summers are rainier than winters comparatively. Precipitation here averages 1299 mm, and the average annual temperature is 26.4 °C in Nabadwip.
In Kharagpur, the average temperature is 26.7 °C, and the average rainfall is 1462 mm. Therefore, the city has a tropical climate.
What the impact of climate over the State?
The amount of rainfall of the season varies from the southern part of Malda to the South facing slopes of the Himalayan region in Darjeeling and Jalpaiguri districts of West Bengal and ranging from the west-central part of Gangetic West Bengal to the coastal belt of south 24- Parganas.
- The amount of rainfall is not uniform throughout the year, but, its distribution varies from year to year and from one region to the other in the same year.
- This variation depends on the following factors –
a)location of the place concerning moisture-bearing monsoon air current
- b) position of land and water
- c) break in the monsoon and its duration
- d) general strength of the monsoon
- e) frequency and movement of depressions and
- f) formation of other low-pressure systems
However, the quantum of rainfall again increases in the coastal regions of Midnapore and 24- Parganas(S).
Note: In recent years, the temperature has increased, and rainfall has decreased gradually, and this may be attributed to the phenomenon of global warming.
- The climate of the State adds to the scenic beauty of the region. Hence, a considerable number of tourists visit such spots- Kalimpong (averagely cool throughout the year), Darjeeling, Siliguri, Mirik, Digha, Cooch Behar, Dooars, Gaur, Bangarh, Sunderbans of Delta etc.
- The plains of West Bengal contribute immensely to crop production as adequate rainfall is observed here.
- Hot wet climate is suitable for the production of rice and jute.
- High rainfall in the Northern Mountainous region is favourable for the production of tea, which is famous all over the world.
- Oilseeds and pulses are also produced in large quantities in the State.
Note: Rice and fish the staple food of the Bengalis because they are easy to digest in this climate and are readily available.
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