Climate and Soil of Bihar | BPSC Preparation: All subjects - BPSC (Bihar) PDF Download

Climate of Bihar

Bihar is situated in the sub-tropical region of the temperate zone, specifically between 23½° to 40° North latitude. It experiences a continental monsoon climate with distinct seasons, including a humid sub-tropical climate. Several geographical factors influence Bihar's climate:

• Proximity to the Tropic of Cancer: Being north of the Tropic of Cancer, Bihar has a warm climate, with summer temperatures sometimes exceeding 45°C.
• Distance from the Sea: The eastern part of Bihar, being closer to the sea, experiences a humid climate, while the western part is relatively dry due to continental effects.
• South-West Monsoon: The activity of the South-West monsoon significantly impacts Bihar's climate, bringing monsoon rains during the summer.
• Himalayan Influence: The northern part of Bihar is cooler due to its proximity to the Himalayan mountains.
• Upper Air Circulation: Changes in upper air circulation also play a role in shaping Bihar's climate.

Rainfall and Weather Patterns

• Bihar receives varying amounts of rainfall, with the eastern part averaging 200 cm and the western part around 100 cm. The eastern part is also affected by Norwesters, which are storms that bring rain during the pre-monsoon period.
• The low-pressure belt that develops over Rajasthan and extends to the Bay of Bengal passes through Bihar, facilitating the arrival of monsoon rains in the summer. Tropical cyclones originating in the Northern Bay of Bengal also significantly impact Bihar's climate.
• After the rainy season, the air retains moisture for an extended period, leading to what is known as a "modified monsoon climate."
• According to different climatic classifications, Bihar's climate is described as:
• Koppen: Monsoon type with dry winters (Cwg)
• Trewartha and Thornthwaite: Sub-tropical humid type

Overview of Seasons in Bihar

Bihar experiences four distinct seasons based on climate factors like temperature, rainfall, and wind direction:

Hot Weather Season

The hot weather season in Bihar spans from March to May. During this period:

• Temperatures rise, and atmospheric pressure decreases.
• March: Marks the beginning of hot weather.
• April: Typically has the lowest humidity.
• May: The hottest month, with average temperatures ranging from 32°C in the West to 29°C in the East and North-East. Gaya often records temperatures as high as 45°C.

Norwesters:

• These are cyclonic winds that bring relief by lowering temperatures and are particularly impactful in the East of Bihar.
• They originate over Bihar and move eastward, bringing much-needed rainfall.

Mango Showers:

• A significant weather phenomenon during this season, these showers are crucial for the early growth of Kharif crops.
• They are characterized by light rain accompanied by thunder and lightning.
• These showers are especially beneficial for crops like jute, paddy, and fruits such as mangoes and litchis.

Hailstorms:

• Hailstorms can occur during this season due to the rising ground air carrying moisture to high altitudes where it freezes.
• This process leads to precipitation in the form of hail.

Regional Variations:

• Western Bihar: Receives about 127 mm of average rainfall.
• Eastern Bihar: Particularly the North-Eastern part, receives about 254 mm of average rainfall.
• Southern Bihar: Generally receives less rainfall compared to Northern Bihar.

South-West Monsoon

The South-West Monsoon season in Bihar typically spans from June to September and is characterized by the following features:

• Onset: The monsoon begins around June, with rain-bearing winds known as South-West Monsoon winds. This period is marked by a low-pressure center developing over the plain region of Bihar and a high-pressure center over the Northern Bay of Bengal.
• Intensity: The onset of the monsoon is often dramatic, featuring intense cyclonic storms accompanied by thunder, lightning, and heavy rainfall.
• Geographic Influence: The monsoon winds are funneled by the Himalayas to the north and the peninsular foreland to the south, leading to substantial rainfall in Eastern and Northern Bihar. The winds first impact North-East Bihar, particularly the Kishanganj district.
• Rainfall Distribution: Rainfall decreases from east to west across the state. For instance, districts like Kishanganj receive over 180 cm of rainfall, while western districts experience significantly less. The overall rainfall varies spatially and temporally, with July and August being the wettest months, and September receiving less rainfall compared to the earlier months.
• Regional Variations: The North-East parts of Bihar can receive over 190 cm of rainfall, while western parts may receive around 100 cm. The area northeast of the Burhi Gandak plain typically receives more than 125 cm of rainfall.

Rainfall in Bihar

• Bihar receives an average annual rainfall of 120 cm, with the rainy season lasting from June to October, contributing 85% to 90% of the total rainfall. The West-central region of Bihar typically receives around 100 cm of rainfall, which increases to between 200 cm and 300 cm in the sub-montane region in the north, particularly in the Purnea and Kishanganj districts. 
• Kishanganj is noted for receiving over 200 cm of rainfall, the highest in the state. Most of the plains receive less than 125 cm of rainfall, while most of the plateau region receives more than 125 cm, with some areas receiving up to 150 cm.

Soils of Bihar

• Soil, a vital mix of minerals and organic materials, forms the foundation for plant growth. It originates from the breakdown of parent rocks through physical and chemical processes, with climate playing a crucial role in its formation. In Bihar, the variation in relief, precipitation, vegetation, and parent rocks has led to the emergence of different soil types.
• Alluvial Soil, constituting about 90% of the soil in Bihar, is the most prevalent. This soil is formed by sediments deposited by rivers in the northern and southern plains of the Ganga River.

Soil of Northern Plain

In the Northern Plain region of Bihar, Alluvial soil, locally known as Kachari soil, is the predominant type, covering the area except for the hilly regions of West Champaran, where forest or mountain soil is found. This soil is primarily the result of sediment deposition by rivers such as the Gandak, Burhi Gandak, Mahananda, Kosi, and Saryu.

The soils of the Northern Plain can be further classified into four types:

Piedmont Swamp Soil

• Located from the northwestern part of West Champaran to the Someshwar hills in Kishanganj, this soil is characterized by its shallow to deep layers containing rocks and pebbles.
• It is mostly clayey, rich in organic matter, and neutral in reaction, making it suitable for crops like rice, maize, and barley. In some areas, excessive rain and moisture have led to the development of marshy land. The soil is light brown or yellow in color and is acidic due to the predominance of forests.

Terai Soil

• Found in a narrow belt along the border of Nepal, from West Champaran to Kishanganj and Araria districts, Terai soil varies in texture, being heavier in the western part and coarser in the southeastern region influenced by the Kosi and Mahananda rivers. 
• It is grey to yellow in color, poorly drained, and has a neutral to moderately acidic reaction. Rich in lime and small gravels, this soil has a medium level of fertility, with lowland Terai soil being more fertile than upland Terai soil.
• In the lowland areas, crops such as rice, sugarcane, jute, maize, vegetables, and oilseeds are grown, while upland areas are mostly barren, with crops like millet, marua, kulthi, sweet potato, and arhar.

Alluvium Soil

• Alluvium soil is found south of the Terai soil belt. This soil stretches in a broad belt that narrows towards the northwest and expands in the southeast direction.
• It is present in various districts, including Purnea, Araria, Katihar, Madhepura, Saharsa, Samastipur, Darbhanga, Madhubani, Muzaffarpur, Supual, Begusarai, and Khagaria.
• The thickness of this soil varies, being thicker in the north and thinner in the south, with a medium level of productivity.
• Important crops that are grown in alluvium soil include jute, paddy, wheat, maize, pulses (such as gram, masur, and khesari), and oilseeds (like mustard).
• The soil consists of sand, loam, and clay in different proportions.
• However, it is deficient in phosphorus and nitrogen, which gives it a characteristic color resembling brown and white.

Soils of Southern Plain

The soil of the Southern Plain is located between the North Ganga Plain and the Southern Plateau (Chotanagpur Plateau). This soil is formed by alluvium deposited by the Son, Punpun, Phalgu rivers and their tributaries.
The soil of this plain is classified into four types:

Karail-Kewal Soil

• Characteristics: Heavy clay soil known for wet paddy lands (dhanhar).
• Location: Spread in the south of Tal soil region, covering areas like North Rohtas, North Gaya, Aurangabad, Patna, Jehanabad, Munger, Bhagalpur, Bhojpur, and Buxar.
• Soil Types: Karail (alkaline soil), Kewal (clay and heavy clay loamy soil).
• Soil Nature: Acidic to alkaline, with colors ranging from deep brown to yellow and light yellow.
• Properties: High water absorption capacity and fertility.
• Crops: Suitable for rice and rabi crops such as wheat, linseed, bajra, pulses, and gram.

Tal Soil

• Location: Spread from Buxar to Banka district, situated in the backwater belt of the Ganga.
• Characteristics: Area remains flooded for months during the rainy season due to poor drainage.
• Soil Width: Varies from 8 to 10 km.
• Soil Color and Texture: Varies from light grey to dark grey, with texture ranging from medium to heavy.
• Soil Reaction: Neutral to slightly alkaline (pH between 7 to 8).
• Crops: Kharif crops cannot be grown due to water accumulation. Rabi crops like wheat, khesari, gram, peas, and lentils are harvested after water drains, with high yields.

Balthar Soil

• Location: Developed between Chota Nagpur Plateau and South Ganga Plain’s transitional zone, found in a narrow belt ranging from 5 to 15 km.
• Characteristics: Less fertile with low water absorption capacity, acidic in nature, dominated by sand and gravel.
• Soil Color: Red and yellow, with red color due to iron content.
• Crops: Maize, jowar, bajra, and gram are the chief crops grown in this soil.

Kagari Soil

• Location: Found on the south banks of the Ganga River and along the banks of Son, Kiul, Punpun, and Phalgu rivers in the form of thick embankments.
• Soil Characteristics: Rich in lime and brown in color.
• Crops: Suitable for maize, barley, chilly, and mustard crops.

Soils of Southern Plateau

The soils of the Southern Plateau are characterized by residual soils found in the narrow Southern Plateau region, known for their red and yellow coloration. These soils are a result of the weathering and disintegration of rocks, primarily igneous and metamorphic.
The soils of the Southern Plateau can be classified into two main types:

Red and Yellow Soils

• Formation: These soils are formed from the disintegration of igneous and metamorphic rocks. The presence of iron in these rocks gives the soil its characteristic red color.
• Fertility: Red and yellow soils are generally less fertile, making them suitable for growing coarse crops and pulses.
• Geographical Distribution: This type of soil is found in the southeastern parts of Bihar, including areas such as Banka, Nawada, Gaya, Aurangabad, Jamui, and Munger (specifically in the Kharagpur hilly region).

Red Sandy Soil of Kaimur Hills

• Location: Red sandy soil is found in the Kaimur range in the west, extending to the Rajmahal Hills in the east, as well as in the northern margin areas of the Northern Chota Nagpur Plateau.
• Characteristics: This soil is yellowish-red in color and is acidic in nature. The higher percentage of sand in this soil results in lower fertility.
• Suitability: Due to its lower fertility, red sandy soil is suitable for growing only certain crops such as bajra (pearl millet) and jowar (sorghum).