Climate of Bihar

Bihar experiences a humid subtropical climate, where the air often carries a quiet heaviness of moisture, and the seasons shift like slow-moving chapters of a familiar story.

The state has three main seasons:

• Summer
• Rainy (Monsoon) Season
• Winter

The annual average temperature ranges from 8°C in December–February to 38°C in April–June.

Factors Influencing the Climate of Bihar

Five major influences shape Bihar’s climate:

• Proximity to the Himalayas
• Proximity to the Tropic of Cancer
• Influence of the Bay of Bengal
• Activity of the South-West Monsoon
• The hot summer winds (Loo) and Western Disturbances

Seasons of Bihar

1. Summer Season (March to June)

• In March, the ITCZ (Inter-Tropical Convergence Zone) begins shifting northward.
• Temperature rises as air pressure decreases.
• Gaya becomes the hottest region, with temperatures reaching up to 45°C.
• From April to early June, a dry, scorching wind known as “Loo” blows, often causing heat-related illnesses and even fatalities.

2. Rainy Season (July to October)

• Nearly 91% of Bihar’s annual rainfall occurs during this season, mainly in June–August.
• By mid-June, the ITCZ reaches the Ganga Plains, activating the South-West Monsoon.
• Bihar receives rainfall from both monsoon branches:
  • Bay of Bengal Branch
  • Arabian Sea Branch

Retreating Monsoon

• After August, the South-West Monsoon gradually weakens and withdraws.
• Rainfall becomes very little or almost absent during this period.

3. Winter Season (November to February)

• Reduced heating of land and dropping temperatures mark the arrival of winter.
• Days grow shorter; nights turn longer and colder.
• December and January record the lowest temperatures.
• Frost is common in the Shiwalik region of North-West Bihar in January, severely damaging crops, especially potatoes.
• Western Disturbances bring light rainfall (5–10% of annual rainfall) during January–February, which benefits Rabi crops.