Pariksha SaathiLesson 7 of 10 · Bihar General Knowledge
Climate, Soils, Forests and Wildlife of Bihar
Drafted with AI assistance and fact-checked on 28 October 2026; not yet read line by line by a human editor. Spotted a mistake? Tell us. Editorial standards & corrections
Climate type
Bihar has a humid subtropical monsoon climate, with hot summers, a wet monsoon and cool, dry winters. Lying wholly north of the Tropic of Cancer and far from the sea, it has a continental quality: summer temperatures in the south-west, around Gaya, often cross 40 °C, dry hot winds called loo blow in May, and winter nights in the north are cold and foggy, with occasional cold waves.
Seasons and rainfall
In April and May, pre-monsoon thunderstorms called nor'westers (kalbaisakhi) bring some relief, mainly in the east. The Bay of Bengal branch of the south-west monsoon arrives around mid-June and gives most of the year's rain by September. Rainfall is heaviest in the north-east, around Kishanganj near the Himalayan foothills, and decreases towards the west and south-west. The late-monsoon Hathiya (Hasta nakshatra) rain at the end of September is vital for the paddy crop, while light winter rain from western disturbances helps wheat. Because rainfall is so uneven, some districts can face floods and others drought in the same year.
Soils
Almost the whole state is covered with alluvium. In the far north-west are piedmont swamp soils at the foot of the hills, followed by terai soils along the Nepal border. In the north-western and central parts of the North Bihar plain, drained by the Gandak and the Burhi Gandak, the new alluvium is calcareous, rich in lime, and suits maize, sugarcane and tobacco. South of the Ganga the alluvium is older: the low tal areas have heavy clay soils that lie under water in the monsoon, hold moisture and suit winter pulses, and other parts of the South Bihar plain have the heavy, sticky clay known locally as karail-kewal. The southern hills and the Kaimur plateau have red and yellow soils, thinner and less fertile.
Forests
Bihar has one of the smallest shares of forest cover among the states, less than a tenth of its area, against the one-third target of the National Forest Policy 1988; most of the old forests went to Jharkhand in 2000. Forests survive in two belts. In the north-west, the Valmiki forests of West Champaran are tropical moist deciduous, with sal as the main tree. In the south, the hills of Kaimur, Rohtas, Gaya, Nawada, Jamui, Munger and Banka carry tropical dry deciduous forest with trees such as sal, khair, kendu, mahua, palash and bamboo.
Valmiki National Park and Tiger Reserve
In the far north-west of West Champaran, between the Gandak and the Nepal border, Valmiki is both a national park and a tiger reserve; it came under Project Tiger in 1989-90. It adjoins Chitwan National Park in Nepal and the Sohagibarwa sanctuary of Uttar Pradesh, so tigers move across a shared landscape. Its name recalls the sage Valmiki, whose ashram is believed to have stood in this area. Besides tigers it shelters leopards, sloth bears, gaur, sambar, chital and hog deer, and one-horned rhinoceroses sometimes wander in from Chitwan.
Vikramshila Gangetic Dolphin Sanctuary
Declared in 1991, it protects the stretch of the Ganga between Sultanganj and Kahalgaon in Bhagalpur district and is regarded as India's first protected area created specially for the Gangetic river dolphin (Platanista gangetica), locally called soons. The dolphin is almost blind and finds its way by echolocation; since it needs clean, deep, flowing water, its presence shows the health of the river. It was declared India's National Aquatic Animal in 2009.
Other sanctuaries and birds
Kaimur Wildlife Sanctuary is the largest in Bihar. Bhimbandh in Munger is known for its hot springs, the Gautam Buddha sanctuary lies in Gaya district, the Rajgir (Pant) sanctuary in Nalanda district and Udaipur in West Champaran. Bird habitats include the Nagi Dam and Nakti Dam bird sanctuaries in Jamui, the Kanwar Lake bird sanctuary in Begusarai, the Kusheshwar Asthan bird sanctuary in Darbhanga and the Salim Ali Jubba Sahni bird sanctuary at Baraila Lake in Vaishali. In winter these wetlands receive migratory ducks and waders from Central Asia and Siberia, and the floodplains near Naugachia in Bhagalpur district are a breeding ground of the greater adjutant stork.
Key facts
- Climate: humid subtropical monsoon; loo in May; nor'westers (kalbaisakhi) in April-May; the south-west monsoon arrives around mid-June.
- Rainfall is heaviest in the north-east (Kishanganj) and decreases towards the west and south-west; the Hathiya rain at the monsoon's end is vital for paddy.
- Soils: piedmont swamp and terai soils in the north-west, calcareous new alluvium in the Gandak-Burhi Gandak plain, older alluvium with tal clays and karail-kewal in the south, red and yellow soils in the southern hills.
- Forest cover: less than a tenth of the area, against the one-third target of the National Forest Policy 1988.
- Valmiki (West Champaran): both a national park and a tiger reserve, under Project Tiger since 1989-90, adjoining Chitwan in Nepal.
- Vikramshila Gangetic Dolphin Sanctuary (1991): the Ganga between Sultanganj and Kahalgaon, Bhagalpur district.
- Gangetic dolphin (soons, Platanista gangetica): almost blind, uses echolocation; declared India's National Aquatic Animal in 2009.
- Kaimur is Bihar's largest wildlife sanctuary; Bhimbandh (Munger) is known for hot springs; Nagi Dam and Nakti Dam are bird sanctuaries in Jamui.
- Wetland bird sanctuaries: Kanwar Lake (Begusarai), Kusheshwar Asthan (Darbhanga), Salim Ali Jubba Sahni at Baraila Lake (Vaishali).
Quick revision
Humid subtropical monsoon climate; loo in May; kalbaisakhi April-May; monsoon from mid-June; rain highest in Kishanganj; Hathiya rain for paddy; calcareous alluvium in Gandak-Burhi Gandak plain, tal clays and karail-kewal south of Ganga, red-yellow soils in southern hills; forest under a tenth (target one-third, policy 1988); Valmiki national park and tiger reserve (Project Tiger 1989-90), next to Chitwan; Vikramshila dolphin sanctuary 1991 (Sultanganj-Kahalgaon); dolphin national aquatic animal 2009; Kaimur largest sanctuary.