Bihar is located in the sub-tropical region of temperate zone. Sub-tropical region is extended between 23½to 40° North and South latitudes. Bihar enjoys a continental monsoon and humid sup-tropical type of climate.
The main geographical factors that affect the climate of Bihar :
➤ Some physical factors like nearness to Tropic of Cancer, nearness to Bay of Bengal, activity of South-West monsoon, adjoining Himalayan mountains and changes in the upper air circulation affect the climate of Bihar.
➤ Eastern part of Bihar experiences humid climate due to nearness to the sea while Western part is comparatively dry due to continental effect. Eastern part receives 200 cm average rainfall while Western part receives 100 cm average rainfall.
➤ Bihar is located near the Tropic of Cancer (North of it), thus, it has warm climate. During summers the temperature of Bihar sometimes exceeds more than 45°C.
➤ Its Northern part is cooler as compared to Southern part due to nearness to the Himalayas.
➤ Bihar also adjoins the Ganga Delta and Assam which are a source region of Norwesters. Norwesters are storms which bring rain in pre-monsoon period.
➤ The low pressure belt which developed over Rajasthan and nearby area later gets extended upto Bay of Bengal through Bihar and Odisha. This leads to arrival of monsoon rains over Bihar in summer season. Tropical cyclone originating in Northern Bay of Bengal also has great impact on its climate.
➤ After rainy season the moisture in the air remains for longer period, thus, its climate can be called as ‘modified monsoon climate’.
➤ According to Koppen, the climate of Bihar is monsoon type with dry winters (Cwg), whereas it is sub-tropical humid type according to Trewartha and Thornthwaite.
Seasons in Bihar
On the basis of climate (such as temperature, rainfall and direction of winds), the seasons in Bihar can be broadly classified into four types.
1. Hot weather season – March to May
2. South-West monsoon – June to September
3. Retreating South-West monsoon – October to November
4. Cold weather season – December to February
1. The Cold Weather Season
➤ This season prevails from December to February. It is characterised by low temperature, light northerly winds, clear skies and low humidity.
➤ Bihar plain experiences cold waves due to pressure differences in North-Western India and South-Eastern India. Temperate cyclonic disturbances (Western disturbance) originating in Mediterranean sea region cause rainfall over this region about 10 to 20 mm, which is beneficial for Rabi crops.
➤ In the North-West Bihar, the adjoining areas of the Shiwalik region have the possibility of frosting which adversely affects the potato crop.
➤ The average temperature of Bihar in this season is recorded to 16°C. January is the coldest month. Gaya records the lowest temperature and is the coldest place of Bihar. During this season plains record higher temperature than plateau region due to higher elevation.
2. Hot Weather Season
➤ The hot weather begins in March, Temperature increases and pressure decreases continuously. It continues till May. In April month, humidity is lowest.
➤ Average temperature during this season ranges between 29°C in the East and North-East to 32°C in the West. Winds blow from North-West in the plain.
➤ The temperature in the East declines due to Norwester (a cyclonic wind) shower impact. It originates over Bihar and moves Eastwards.
➤ Norwester brings rainfall in Bihar and is accompanied by lightening, thunderstorm and hailstorm. However, it is extremely helpful for pre-Kharif crops like jute, paddy and a number of fruits like mango and litchi. Such rainfall is known as ‘Mango Showers’ or ‘Kal Vaisakhi’.
➤ Gaya is hottest district in May.
➤ During this season hailstorm occurs due to rising of the ground air so high that the moisture reaches above the freezing level of the atmosphere and precipitation comes down in the form of hails.
➤ The hot scorching ‘loo’ winds blow in the plains during late April and May having an average velocity of 8-16 km per hour. Loo are local winds which affect human comfort especially in Gaya, Jehanabad, Aurangabad, Nawada, Nalanda and Saran districts.
➤ During this season, the Western part of Bihar receives about 127 mm average rainfall while the eastern part especially North-Eastern part receives about 254 mm average rainfall.
➤ This summer rainfall is important for jute and Bhadai crops (Autumn harvest) like paddy, marua and so on.
➤ The Southern part of Bihar receives comparatively lesser rainfall than Northern Bihar.
3. South-West Monsoon
➤ This season starts in June and lasts upto September. Over the plain region a low pressure center develops while high pressure center develops over the Northern Bay of Bengal Sea.
➤ This pressure difference causes rain bearing winds to blow towards Indian plain. These are known as South-West Monsoon winds.
➤ During this season, July and August are the rainiest months.
➤ The burst of monsoon in Bihar is accompanied with the sudden arrival of intense cyclonic storms with thunder, lightening and torrential rain.
➤ The passage of these rain bearing winds are constricted by the Himalayas in the North and foreland of the peninsular India, which cause heavy rainfall in Eastern and Northern Bihar. These winds first strike in the North-East Bihar i.e. in Kishanganj district.
➤ As a number of cyclones visit the transitional belt of Bihar which lies between wet West Bengal and dry Uttar Pradesh, the rainfall decreases from East toWest direction.
➤ The South Bihar region records generally less rainfall. It is due to the reason that when rain bearing winds constricted by the Himalayan mountains in the North then, these rise above and give more rain in the Shiwalik range, Terai region and Northern Bihar plains as compared to South Bihar region. Thus, the North Bihar plain receives 100 cm to 200 cm rainfall.
➤ ‘Hathiya’ has great importance during monsoon season in Bihar. Rainfall occurs in this Nakshatra greatly affects the Rabi crops. It is also associated with rainfall of October.
4. Retreating South-West Monsoon
➤ In the first week of October, South-West monsoon winds begin to retreat. It is a transitional period from summer to winter and also known as ‘Sharad season’.
➤ In this month, the seasonal low pressure disappears and the North-Westerly winds begin to blow over the plains from the high in the North-West India towards the low depression which develops over the Bay of Bengal.
➤ The more striking feature of this season is the arrival of tropical cyclones which develop in the Bay of Bengal at about 12° N latitude.
➤ During this season, Jet streams (responsible for origin of monsoon) become South cold waves of the Himalayas. Westerlies and Northern winds start to blow over the plain region. These are responsible to bring down the temperature and create dry condition.
➤ In the period of Hathiya Nakshatra (September – October), the frequency of these tropical cyclone is maximum in Bihar state. These cyclones are considered beneficial for the paddy crop in the state.
➤ Sometimes, the state gets incessant rain casuing floods. During this season, the North-Eastern and Eastern Bihar gets less than 10cm rainfall and the North-Western Bihar gets less than 2. 5cm rainfall. November month remains almost dry.
Distribution of Rainfall in Bihar
➤ The average annual rainfall in Bihar is 120 cm. This rainy period remains from June to October which gives 85% to 90% rainfall to the state. The West-central region receives a normal rainfall about 100 cm which increases to 200 cm towards the sub-montane region in the North, especially Purnea and Kishanganj districts.
Kishanganj receives more than 200 cm rainfall, which is highest in the state.
➤ The greater part of the plains receive less than 125 cm rainfall whereas most of the plateau receives more than 125 cm rainfall which increases to 150 cm.
Soils of Bihar (Bihar GK in English)
Soil is the mixture of mineral and organic components which are the basis of plants growth. Soil is formed from breaking down of parent rocks or physical and chemical changes occurring in parent rocks.Climate also play-important role in soil formation. Variation in relief, precipitation, vegetation and parent rocks have resulted in various types of soil in Bihar. In Bihar, Alluvial soil is extensively found i.e. 90%. This soil has been formed by sediments deposited by rivers in the North and South plains of Ganga river.
Classification of Soils on the Basis of Landforms and Moisture
The Agricultural Research Institute of Bihar has divided the soil’s of Bihar into three categories on the basis of characteristics such as parent rocks, landforms, moisture, physical and chemical properties. These are given below:
1. Soils of Northern Plains 2. Soils of Southern Plains 3. Soils of Southern Plateau
1. Soils of Southern Plain
The soil of Southern plain is found between North Ganga plain and Southern plateau (Chotanagpur plateau). This is formed by alluvium deposited by Son, Punpun, Phalgu rivers and their tributaries.
The soil of this plain is divided into four types. i. Karail-Kewal Soil ii. Tal Soil iii. Balthar Soil iv. Kagari Soil
i. Tal Soil
➤ This soil is spread from Buxar to Banka district. This is situated in backwater belt of the Ganga. The area remains under water for months during rainy season due to accumulation of rain water and poor drainage.
➤ The Tal soil varies in colour from light grey to dark grey and in texture from medium to heavy soil.
➤ Due to accumulation of water for considerable period of time, kharif or monsoon crops cannot be grown in this soil.
➤ Rabi or spring crops like wheat, khesari, gram, peas, masoor, lentils, etc are harvested in this soil after water dries up and their yield is quite high.
ii. Karail-Kewal Soil
➤ This is heavy clay soil and characterised by wet paddy lands or dhanhar, spread in the South of Tal soil region.
➤ Karail is an alkaline soil and Kewal is clay and heavy clay loamy soil.
➤ This soil is acidic to alkaline in nature with deep brown to yellow and light yellow in colour.
➤ This is highly balanced with high water absorption capacity and high fertility in nature. It is well suited for both rice and rabi crops such as wheat, linseed, bajra, pulses and gram.
iii. Balthar Soil
➤ It is developed between Chota Nagpur plateau and South Ganga plain’s transitional zone.
➤ It is found in Kaimur plateau to Rajmahal hills in narrow belt ranging from 5 to 15 km.
➤ The soil is less fertile and has less water absorption capacity.
➤ It is acidic in nature and is dominated by sand and gravels. This is red and yellow in colour. The soil is red in colour due to the presence of iron contents.
➤ Maize, jowar, bajra, gram are chief crops grown in this soil.
iv. Kagari Soil
➤ This soil is found in the South banks of Ganga river and on the banks of Son, Kiul, Punpun and Phalgu rivers in the form of thick embankments.
➤ It is rich in lime and brown in colour.
➤ It is suitable for maize, barley, chilly and mustard crops.
2. Soil of Northern Plain
Alluvial soil (locally known as Kachari soil) is found all over this region except the hilly areas ofWest Champaran in Shiwalik range. The mountainous areas of Shiwalik range has forest or mountain soil. The soil here is the result of deposition of sediments brought by Gandak, Burhi Gandak,Mahananda, Kosi and Saryu rivers.
North plain soils can be classified into four types. i. Piedmont Swamp Soil ii. Terai Soil iii. Alluvium Soil iv. Domat Soil
i. Terai Soil
➤ This type of soil is found in Northern part in a narrow belt along the border of Nepal to the South of Someshwar range and from West Champaran to Kishanganj and Araria districts.
➤ This soil is heavy in texture in the Western part while the soil of the South-East region has high texture due to the influence of the Kosi and Mahananda rivers.
➤ This soil is grey to yellow in colour which is not well drained and neutral to moderately acidic in reaction. It is rich in lime and has small gravels.
➤ It has a medium order of fertility. The lowland Terai soil is more fertile compared to upland Terai soil.
➤ In the lowland Bhadai and Aghani crops like rice, sugarcane, jute, maize, vegetables and oilseeds are grown while the uplands remain mostly barren with growth of mainly millet, marua, kulthi, sweet potato, arhar, etc.
ii. Piedmont Swamp Soil
➤ This soil is found in North-Western part of West Champaran district to Someshwar hills (Kishanganj) in the East. This soil is shallow to deep and has rocks and pebbles.
➤ This soil is mostly clayey, rich in organic matter and neutral in reaction. This supports good rice crop, maize and barley crops.
➤ Marshy land has been developed in this soil at some places due to excessive rain and moisture. It is light brown or yellow in colour and acidic in nature due to the predominance of forests.
iii. Alluvium Soil
➤ This soil lies South of the Terai Soil belt. This is a broad belt which tapers towards North-West and broadens in the South-East.
➤ This soil is thicker towards North and thinner towards South and has medium productivity.
➤ Important crops grown in this soil are jute, paddy, wheat, maize, pulses like gram, masur, khesari and oilseeds like mustard, etc.
➤ The soil is deficient in phosphorus and nitrogen due to which it resembles as brown and white in colour.
The soil is further divided into two types, such as:
New Alluvium or Khadar Soil
➤ This is a newer alluvium soil which is found in lowlands and in the vicinity of rivers where fresh deposits renew it periodically.
➤ It is sandy in the upper reaches while silty in the lower section. The soil is less calcareous and carbonatic than Bhangar soil and has less kankar concentration.
➤ Surface of Khadar soil is levelled due to periodic deposition of silt. Khadar soil is suitable for crops like wheat, paddy, etc.
➤ Due to having better drainage except in river beds, it has low percentage of humus and nitrogen and little lime, thus is more suitable for many crops.
➤ It is dark brown in colour. It is extended in Ganga valley and lower valleys of Gandak, Burhi Gandak, Kosi and Mahananda rivers.
➤ It is mainly found in flood prone regions and is extensively found in Purnia and Saharsa districts. Jute is also grown in this soil in the North-Eastern parts of Bihar due to having higher rainfall.
Old Alluvium or Bhangar Soil
➤ This is an older Alluvial soil which is found in Western parts of Ghaghara-Gandak Doab and Burhi Gandak. It is mostly loamy with high clay factor.
➤ Its drainage is poor due to high clay concentration. This makes the soil sticky.
➤ Kankar or carbonaceous compounds are abundant in this soil.
➤ The difficulty in its tillage makes it suitable for paddy cultivation. It is rich in lime (more than 30%) and potash which makes it suitable for sugarcane cultivation.
➤ This soil is under the process of denudation. The sub-soil has an impervious clay layer.
Bhangar has two varieties of soils such as :
— Balsundari Soil It is found from the Southern part of Purnea to Saharsa, Darbhanga, Muzaffarpur, Siwan, Saran and Gopalganj district. It is rich in lime which is suitable for fruits like mango, banana and litchi, and crops like paddy, sugarcane, wheat, maize, tobacco, etc.
— Bhat Soil The Central-Western North Bihar plains in the lower Gandak valley have Bhat or calcareous soil. It is a chemical variant of the alluvial soil.
iv. Domat Soil
➤ It is found in a broad belt in the South-western portion of the North-Bihar plain.
➤ The Eastern region is dominated by young calcareous alluvial soils while Western part especially Siwan and Saran districts have young calcareous alluvial soil with saline and alkali soil.
➤ The Eastern domat soil is white to olive grey in colour but appears dark grey in the vast lowlying area of this region which are known as ‘Chaurs’. This soil has medium to high fertility.
➤ Important crops which are grown in this soil are maize, paddy, wheat, sugarcane, tobacco, etc. Mango and litchi are also grown here especially in Muzaffarpur and Vaishali districts and Banana is majorly grown in Vaishali district, especially around Hajipur city.
3. Soils of Southern Plateau
Residual soils which are found in the narrow Southern plateau region and are red and yellow in colour are known as soils of Southern plateau.
The soils of Southern plateau are divided into two types:
i. Red Sandy Soil of Kaimur Hills
➤ This soil is found in the Kaimur range in the West to Rajmahal Hills in the East and the Northern margin areas of Northern Chota Nagpur plateau.
➤ It is yellowish red in colour and is acidic in nature.
➤ Higher percentage of sand results in lesser fertility of this soil thus, it is suitable only for bajra, jowar, etc crops.
ii. Red and Yellow Soils
➤ These soils have been formed from disintegration of igneous and metamorphic rocks.
➤ Due to presence of iron in the rocks, their colour is red.
➤ They are less fertile and thus suitable for coarse crops and pulses.
➤ This soil is found in the South-Eastern Bihar such as Banka, Nawada, Gaya, Aurangabad, Jamui and Munger (Kharagpur hilly region.)