In this guide
A year in Bihar runs through extremes. In May and June, the loo — a hot, dry westerly wind — makes afternoons dangerous. In July and August, rivers overflow in the north. By December and January, dense fog blankets the plains and cold waves chill the villages. Understanding Bihar's climate and soils is essential not only for the geography paper but for answers on agriculture, disasters and health.
Climate type
Bihar has a humid subtropical monsoon climate, with some continental features because of its distance from the sea.
| Season | Months (approx.) | Features |
|---|---|---|
| Summer | March – mid-June | Hot; temperatures often above 40 °C in May–June; the loo (hot westerly winds); occasional thunderstorms (nor'westers, locally called kalbaisakhi) in the east |
| Monsoon | Mid-June – September | The south-west monsoon brings most of the year's rainfall |
| Retreating monsoon | October – November | Occasional cyclonic rain from the Bay of Bengal |
| Winter | December – February | Cool to cold; fog; cold waves; light winter rain from western disturbances |
Rainfall
- Average annual rainfall is roughly 1,000–1,500 mm, but it varies considerably.
- The monsoon enters Bihar from the Bay of Bengal branch, so rainfall generally decreases from east to west and from north to south.
- The north-east (Kishanganj, Purnia, Araria) receives the highest rainfall.
- The south-west (parts of Gaya, Aurangabad, Rohtas, Kaimur) receives less and is more drought-prone.
- Rainfall in the Nepal catchment of north Bihar's rivers matters as much as rainfall within Bihar for floods.
Regional climate contrasts
| Region | Climate character |
|---|---|
| North-east Bihar | Wettest; floods; high humidity |
| North-west Bihar | Moderate rainfall; flood-prone rivers from Nepal |
| South Bihar plain | Less rain; hot summers; drought risk |
| Southern hills | Slightly cooler; thin soils |
Extreme weather
| Hazard | Details |
|---|---|
| Floods | North Bihar every monsoon (see our guides on the Kosi and disasters) |
| Drought | South and south-west Bihar; deficient monsoons also affect the north |
| Heatwaves | May–June; health risks, especially for outdoor workers |
| Cold waves and fog | December–January; affect health, transport and crops |
| Lightning | Bihar records many lightning deaths every year, especially during the pre-monsoon and monsoon; farm workers in open fields are most at risk |
| Hailstorms and unseasonal rain | Damage to rabi crops and mango and litchi orchards |
Bihar has introduced lightning early-warning messages and awareness campaigns; the Indravajra app has been promoted by the state for lightning alerts.
Soils of Bihar
| Soil | Where | Features | Suited to |
|---|---|---|---|
| New alluvium (khadar) | Near rivers, flood plains | Light, fertile, renewed by floods | Rice, maize, vegetables, jute (east) |
| Old alluvium (bhangar) | Higher parts of the plains | Older, more mature; may contain kankar (lime nodules) | Wheat, rice, pulses |
| Tal soil | Low-lying lands on the south bank of the Ganga (e.g., Mokama tal) | Heavy clay; flooded in the monsoon | Rabi pulses (gram, lentil) |
| Diara soil | River islands and banks | Sandy to loamy, deposited by floods | Vegetables, maize, melons after floods |
| Piedmont swamp soil | North-west (Champaran) near the foothills | Waterlogged | Rice |
| Terai soil | Along the Nepal border | Moist, fertile | Rice, sugarcane |
| Red and yellow soil | Southern plateau fringe (Kaimur, Gaya, Jamui, Banka) | Less fertile; low water retention | Coarse grains, pulses |
| Balsundari soil | Parts of north Bihar | Calcareous (lime-rich) alluvium | Wheat, maize, sugarcane |
Soil problems
| Problem | Where / cause |
|---|---|
| Waterlogging | North Bihar, due to floods, embankments and poor drainage |
| Sand deposition | After floods (e.g., post-2008 Kosi) — fields buried in sand |
| Soil erosion | Southern hills and riverbanks |
| Nutrient deficiency | Intensive cropping, imbalanced fertiliser use; zinc and sulphur deficiencies |
| Alkalinity | Patches in some districts |
Implications for agriculture
- Kharif: rice dominates; maize in north Bihar.
- Rabi: wheat, gram, lentil (especially in tal lands), mustard.
- Zaid (summer): vegetables, moong, maize.
- Floods and waterlogging favour crops like makhana in wetlands and require flood-tolerant rice varieties.
- Drought-prone south Bihar needs water harvesting and drought-tolerant crops.
Practice
Prelims-style:
- From which branch of the monsoon does Bihar receive rain?
- Which part of Bihar receives the most rainfall?
- What is tal soil suited for?
- Where are red and yellow soils found in Bihar?
- What is the loo?
Mains-style:
- "Bihar suffers from both floods and droughts in the same year." Explain.
- Discuss the causes of high lightning fatalities in Bihar and suggest measures.
A note on dates and numbers. Exam patterns, vacancies and schedules change from year to year. Always confirm the current details in the latest notification on the Bihar Public Service Commission website .
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