Geography of Bihar

Location and size

• Bihar lies between about 24°20′–27°31′ N and 83°19′–88°17′ E.
• Area: about 94,163 km². It became landlocked after Jharkhand was carved out on 15 November 2000.
• Borders: Nepal (north), West Bengal (east), Jharkhand (south) and Uttar Pradesh (west).
• Administrative units: 38 districts in 9 divisions (Patna, Magadh, Tirhut, Saran, Darbhanga, Kosi, Purnia, Bhagalpur and Munger).
• Population (Census 2011): 10.41 crore (third in India), with a density of 1,106 per km², the highest of any state.
  • Sex ratio 918, literacy 61.8%, urban share 11.3%.
• The 2023 caste survey counted about 13.07 crore people.
  • EBC about 36%; BC about 27%; SC about 19.7%; ST about 1.7%; unreserved about 15.5%.

Physiographic divisions

1. Shivalik (sub-Himalayan) region: in the north-west of West Champaran, including the Someshwar and Ramnagar Dun ranges. Someshwar is the highest point of Bihar, about 880 m.
2. The Ganga plain, covering most of the state:
   • North Bihar plain: Kosi, Gandak, Bagmati and Burhi Gandak. It has chaurs (low wetlands), tals and oxbow lakes, and is very fertile but floods often.
   • South Bihar plain: narrower, with tals such as Mokama and Barahiya. These are flooded in the monsoon and used for rabi pulses in winter.
3. Southern plateau fringe:
   • the Kaimur plateau (Rohtas and Kaimur), part of the Vindhyas;
   • the hills of Rajgir, Gaya, Nawada, Munger (Kharagpur hills) and Jamui, which are outliers of the Chhotanagpur plateau.

Rivers

River	Side	Notes
Ganga	—	Enters at Chausa (Buxar) and leaves near Pirpainti. It flows about 445 km in Bihar and divides the state into north and south
Ghaghara (Saryu)	North	Meets the Ganga near Chhapra
Gandak (Narayani)	North	From Nepal; Valmikinagar barrage; meets the Ganga at Hajipur–Sonpur
Burhi Gandak	North	Meets the Ganga near Khagaria
Bagmati, Kamla-Balan	North	Floods in Mithila
Kosi	North	"Sorrow of Bihar"; formed by the Sun, Arun and Tamur Kosi; shifted far west over two centuries; Kosi barrage (Bhimnagar); 2008 Kusaha breach
Mahananda	North-east	Seemanchal (Kishanganj, Purnia, Katihar)
Son	South	From Amarkantak; Indrapuri barrage (Dehri); meets the Ganga near Maner
Punpun, Phalgu, Kiul	South	Seasonal; the Phalgu at Gaya is linked to pinda daan
Karmanasa	South-west	Part of the UP–Bihar border

• Floods:
  • North Bihar is about three-quarters flood-prone.
  • Causes: heavy rain in the Nepal Himalaya, high silt loads, low gradient, embankment failure and drainage congestion.
  • Responses:
    • embankments, which have their own drawbacks;
    • the proposed Kosi high dam with Nepal;
    • the Kosi–Mechi intra-state link, cleared for central funding;
    • flood forecasting;
    • "jal-jeevan-hariyali" (2019), which revives ponds and ahars.
• Drought: south Bihar suffers drought, eased by ahar-pyne, the traditional irrigation of Magadh.

Climate and soils

• Climate: humid sub-tropical monsoon.
  • Rainfall is about 1,000–2,000 mm, with the most in the north-east (Kishanganj) and the least in the west.
  • Hot "loo" winds blow in summer, and nor'westers bring pre-monsoon storms.
• Soils:
  • New alluvium (khadar) in the north, including the calcareous soils of north-west Bihar;
  • old alluvium (bangar) and tal soils in the south;
  • red and yellow soils on the southern plateau fringe.

Forests and wildlife

• Forest and tree cover is about 10% of the area (Forest Survey reports), much of it in West Champaran, Kaimur, Rohtas, Gaya, Nawada and Jamui.
• Valmiki Tiger Reserve (West Champaran) is the only tiger reserve.
• Sanctuaries:
  • Kaimur (the largest);
  • Bhimbandh (Munger, with hot springs);
  • Gautam Buddha (Gaya);
  • Rajgir;
  • Vikramshila Gangetic Dolphin Sanctuary (Bhagalpur), for the national aquatic animal;
  • Kanwar Lake (Begusarai);
  • Nagi–Nakti (Jamui);
  • Udaipur (West Champaran).
• Ramsar sites: Kanwar Lake (2020), and Nagi and Nakti dams (2024).

Minerals, energy and industry

• Most minerals went to Jharkhand in 2000.
• What remains:
  • limestone and pyrite (Rohtas, Kaimur);
  • mica (Gaya, Nawada, Jamui);
  • gold reserves reported at Karmatiya–Sono (Jamui), which are unmined;
  • glass sand;
  • saltpetre.
• Industry:
  • Barauni refinery and fertiliser plant (Begusarai);
  • sugar mills (West Champaran, Gopalganj);
  • Bhagalpur silk (tussar);
  • railway factories at Madhepura (electric locomotives) and Marhaura (diesel locomotives);
  • thermal power at Barh, Kahalgaon, Nabinagar and others.

Agriculture

• About three-quarters of workers depend on farming.
• Main crops:
  • rice (kharif);
  • wheat and maize (rabi). Bihar is one of the top maize states, with winter maize in Kosi and Seemanchal;
  • pulses in the tal lands.
• Specialities:
  • makhana: Bihar grows about 85–90% of India's output. Mithila Makhana has a GI tag, and a Makhana Board was announced in the 2025 Union Budget;
  • litchi (Muzaffarpur);
  • vegetables;
  • Magahi paan.
• GI tags:
  • Shahi litchi, Katarni rice, Jardalu mango, Magahi paan, Mithila makhana;
  • Silao khaja, Madhubani painting, Sujni and Sikki craft, Bhagalpuri silk and Manjusha art.
• Agriculture road maps: the fourth road map runs 2023–28.

Exam tip: Make a district-wise list of rivers, sanctuaries, GI products and industries. BPSC often asks "which district" questions, and the map of rivers north and south of the Ganga is a favourite.

See it on the map: explore every Bihar district, with rivers and key facts, on the District Atlas.