Climate of Bihar

• Bihar completely lies in the sub-tropical region of tempered zone and its climatic type is Humid Sub-tropical (Cwa).
• Several factors, such as great distance from the sea, adjoining Himalayan mountains, the movement of air fronts from Bay of Bengal and Arabian sea, height from the sea level, etc. affect the climate of Bihar.
• The factors affecting the climate of Bihar are:

1. 1. It extends from 24-degree north to 27-degree north latitude. Hence, its location is in sub-tropical region.
   2. The Himalayan mountains in the north have a significant bearing on the distribution of monsoon rainfall in Bihar.
   3. Bihar joins the Ganga delta and Assam.

• Bihar lies in a belt of transition between the wetter portion of Bengal and drier portion of Uttar Pradesh.
• The summer heat is neither as intense as in the drier west nor so humid as in Bengal. Hot westerly wind starts in March and last upto April and May. But in April and May light, damp, easterly wind blows intermittently, and afternoon storms accompanied with rain take the place of rainless dust-storms of Uttar Pradesh.
• The monsoon rain come to Bihar a little later than in West Bengal and end a little earlier so that the rainfall, though much less than in Bengal, is considerably higher than in U.P.
• The condition in winter is similar to those of U.P. though the rainfall is less and the temperature slightly higher.
• The climate of Bihar can be divided into three season:

1. 1. Hot-weather season from Mid-March to Mid-June.
   2. Rainy season from Mid-June to Mid-October, and
   3. The cold weather season from November to February.

• On the basis of soil characterization, rainfall, temperature and terrain, four major agro-climatic zones have been identified in Bihar-

1. 1. North-West Alluvial Plain (Zone-1),
   2. North-East Alluvial Plain (Zone-II),
   3. South-East Plateau Region (Zone-IIIA),
   4. South-West Alluvial Plain (Zone-IIIB),

Three seasons of Bihar

The Hot-weather Season

• This season covers the months from March to May. It is characterized by great heat and aridity. In March, the mean temperature varies between 23°C to 27°C. The mean maximum is about 32°C and the mean minimum between 15°C to 18°C.
• Due to comparatively low temperature in the eastern part, it comes under the effect of Norwester showers. By the end of may, Gaya records the maximum temperature (40.7°C) however the maximum temperature of 47°C has been recorded in Patna is 42°C and in Muzaffarpur is 41°C
• In April and May, the thermometer rises above 37°C for some hours during the day. The hottest month is
• The mean temperature exceeds 32°C everywhere in the month of May except in the area adjoining Nepal in extreme North-West.
• Afternoon or evening storm which burst into rain after the heat of the day is the characteristic feature of the season. It forms the chief source of rain during this period of the year.
• The hot-weather rainfall is beneficial for the fruits like Litchi and Mango and also help the timely preparation of fields for autumn harvest (Bhadai harvest).

The Rainy Season

• Monsoon arrives in Bihar in mid-June. The month of July and August forms the rainiest months of the year, when nearly 70% of the annual rain takes place in rainy season.
• The rainfall decreases steadily passing from east to west up the valley, and from north to south from the foot of the Himalayas towards the Ganga.
• Monsoon rain in the month of June helps in decreasing the temperature.

The Cold-weather Season

• The rainy season in mid of October and is followed by a period of warm, sunny weather. Although the sun shines, the temperature keeps on falling and cold season begins in the month of November.
• The mean temperature is roughly 21°C in November In December, the mean temperature falls by six to eight degrees. Days are less warm and nights are cold. January is very much like December.
• The cold weather season is cloudless, clear and sunny. A little rainfall takes place in the winter season which is due to the cyclonic storm that travels eastward along a fairly well-defined belt down the Indo-Gangetic plains from
• Persia and Afghanistan, and usually ends before they reach West Bengal. They bring enough clouds obstructing the sunlight for about 15 days, but causes little rain. This small rainfall is very important for rabi crops.