Climate and Soils of West Bengal
West Bengal experiences great climatic variations, due to topography and geographical location. The Northern region remains cool throughout the year due to the presence of Eastern Himalayas while Southern Bengal has a moderate climate due to the influence of the sea. The state has six varieties of soil including the most fertile new alluvial soil.
The climate of West Bengal varies from tropical Savannah in the Southern portion of the state. The Northern region witnesses a humid subtropical type of climate.
Overall the state experiences a tropical monsoon type of climate. Mountain zone and Eastern plains get plenty of rainfall while Western plateau is comparatively dry. The state also enjoys many seasons.
Seasons in West Bengal
West Bengal’s climate can be divided into five seasons:
Hot Weather/Summer Season
In this season, the whole of West Bengal receives vertical rays of the Sun and the landmass gets heated. Temperature ranges from 35°-45°C. This season covers the period between March to mid-June. May is the hottest month of this season. The Western part of the state records a high temperature than the Eastern part. The average temperature in the mountainous regions of the state remains between 15-20°C. Here the summers are pleasant. In hot weather season highest temperature i.e. 45°C is recorded in Asansol city of West Bengal. At night, a cool Southerly breeze blows which carries moisture from the Bay of Bengal. In these hot summer months, thunderstorms called Nor-westers or Kal Baisakhi occur in West Bengal due to cyclones originating in the Bay of Bengal. Such stormy winds are good for paddy and jute.
South-West Monsoon/Rainy Season
The intense heat in Northern India develops a low-pressure system that attracts rain-bearing winds from the sea. These winds blow from the South-West and are known as the South-West monsoon winds. Around 10-15 June, the whole of West Bengal comes under the influence of South-West monsoon and heavy rainfall occurs in all parts of the state till September. The state gets 90% of its rainfall from the Bay of Bengal branch of South-West monsoon. The highest rainfall in West Bengal is recorded at the foothills of the Himalayas. Darjeeling, Coochbehar and Jalpaiguri districts get the heaviest rainfall in the state i.e. about 200-400 cm. The coastal areas of West Bengal also receive heavy rainfall i.e. about 200 cm. The Delta plains receive 150-200 cm of rainfall while Western plateau area i.e. Bankura and Purulia are comparatively drier with 100-150 cm of rainfall. Buxa Duar in Jalpaiguri receives the highest rainfall in the state while Mayureswar in Birbhum receives the lowest rainfall.
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 that 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.
Cold Weather Season
West Bengal is partly under the influence of the North-East trade winds from December to February. These winds blow offshore and have no moisture. As a result, there is no rainfall in the winter months. In this season, the average temperature is between 7°C and 26°C. The temperature over the Western plateau areas drops considerably but this region does not become as cold as the mountainous districts in the North. The Darjeeling Himalayan hill region experiences a harsh winter with occasional snowfall at places.
Mid-February to mid-March is the spring season in Bengal. This short season has pleasant weather, temperature between 20-30°C, and no rainfall. This is the most pleasant season over the plains of West Bengal. There is a slight chill during the night while days are pleasant. There is occasional rainfall or light showers due to Western disturbances in North India.
Soils of West Bengal
The interaction of a wide range of geographic and climatic variations, vegetation have resulted in the formation of different type of soils in West Bengal. Department of Agriculture categorized the soils into six groups on the basis of the analysis of soil profile.
- Mountain and Forest Soil
- Old Alluvium
- New Alluvium
- Red Soil
- Laterite Soil
- Saline Soil
1. Mountain and Forest Soil
The Northern region of West Bengal has mountain soil. This soil is formed by the process of weathering of igneous and metamorphic rocks. It is less fertile and black in color. The soil is good for tea, pineapple, oranges, and pears cultivation.
It is present at an elevation of 2550 m in Darjeeling and Kalimpong districts. The region below the mountains i.e. ‘the duars’ are thick forests that consist of forest soil. The forest soil has acidic humus and low base exchange capacity. In some areas, the forest soil is often sandy and gravelly, much coarser than the soils of the plains. It is present in Alipurduar, Jalpaiguri and Coochbehar districts. Forest soil is also called Terai soil since it is present in the Terai region.
2. Old Alluvium
This soil is comparatively old in age and also called Bhangar. This soil is distributed in the tract lying North of the Ganga containing the districts of North, South Dinajpur, Malda, Eastern Birbhum, and some parts of Murshidabad, Bankura, and Birbhum. The Barind area of Bengal consists of quasi lateritic alluvium. It is good for paddy, wheat, and sugarcane cultivations. This
soil is clayey in texture, acidic, rich in potash and phosphorus, and has a moderate amount of nitrogen and humus.
3. New Alluvium
This soil comparatively new than old alluvium and is also called Khadar. This soil is found along the banks of the rivers. The soil is sandy loam to clayey in texture. New alluvium soil is found in the plains of West Bengal, South of the Bhagirathi river up to the mouth of the Hooghly river. Murshidabad, Nadia, Howrah, and North 24-Parganas consist of new alluvium soil. It is good for paddy, wheat and jute cultivation. This soil is very fertile in nature as new organic material is deposited during floods that make the soil more fertile. The soil has high humus content, high water holding capacity, and is less acidic.
4. Red Soil
This soil is found in the districts of Birbhum, Bardhaman, Bankura, Midnapore, some parts of Malda, and Dinajpur. The presence of ferrous oxide makes the soil red, reddish-brown, or red-black in color. This soil has low water holding capacity. It is poor in nitrogen, phosphate, and high in potash and lime. This soil is mildly acidic and requires nitrogenous and phosphatic manuring. This soil is infertile in nature. Agriculture in this soil is practiced with the help of irrigation. Paddy is the chief crop grown in this soil.
5. Laterite Soil
This soil is found in the Western plateau region. This soil is found in the districts of Birbhum, Bardhaman, Bankura, Purulia, Midnapore, some areas of Barind and Mudhupur forest areas. This soil is red in color. This soil is infertile but with proper irrigation, little vegetation can be done in this soil. The laterite soil is acidic, poor in organic matter, calcium, phosphates, and nitrogen. Soil erosion leaching makes this soil infertile.
6. Clayey Saline Soil
The Sundarbans and the coastal areas of the state have this type of soil. The soil is bluish in color. It is acidic and has very loose particles due to excess organic matter. This soil is not suitable for cereals crop cultivation as it lacks the essential nutrients. It is good for the cultivation of plantation crops such as coconut, betel nut, and watermelon. It remains wet and saline for the most part of the year. This type of soil is present in the Southern part of South 24 Parganas and Midnapore.
Soil Erosion in West BengalSoil erosion is the removal of the top layer of soil by different agents like wind, running water, etc. There are many man-made factors that cause soil erosion such as deforestation, overgrazing, faulty ways of agriculture, shifting cultivation, etc. In West Bengal, around 20% of the land is degraded due to soil erosion and rendered unfit for agriculture. Major causes of soil erosion and preventive measures in West Bengal are discussed below: Mountain Region of North Bengal Sloping topography and heavy rainfall in the districts of Darjeeling, Kalimpong, Jalpaiguri, Alipurduar and Coochbehar causes heavy soil erosion. Landslides, deforestation, shifting cultivation and excess siltation in mountain rivers increase the erosion of mountain and forest soil. Cultivation along the hill slopes, terrace farming afforestation are some of the preventive measures. Plain Areas of Bengal Annual floods, waterlogging, prolonged wet and dry spells of rainfall, deforestation, faulty ways of cultivation are the main causes of soil erosion in delta plains of West Bengal. It takes place in the districts of N&S Dinajpur, Malda, Murshidabad, Nadia, Hooghly, and East Medinipur. Preventive measures are afforestation, construction of dams, measures that can be adopted in agriculture are contour plowing, strip cropping, creating shelterbelts, etc. Western Plateau Poor water retention capacity of the soil, prolonged dry periods resulting in droughts, deforestation, overgrazing, leaching, and seasonal floods are the main causes of soil erosion in the
Western Plateau region of West Bengal. It takes place in Bankura, West Medinipur, Bardhaman, and Purulia. Preventive measures are the construction of dams making embankments, check dams, planting trees (silviculture). Contour ploughing, strip cropping, creating shelter belts are agricultural methods that should be adopted. Coastal Areas Waterlogging, high salinity, very poor water retention capacity, tidal waves, coastal runoff, excess siltation of rivers are the main causes of soil erosion in the coastal regions of West Bengal. These areas include North and South 24 Parganas, East Midnapore, Howrah, and some parts of Hooghly districts. Preventive measures are the construction of drainage canals, raising sea embankments, making sea dykes, planting trees (silviculture), etc.
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