Climate
The cold weather commences early in November and comes to an end
in the middle of March.
The hot weather then sets in and lasts till the
middle of June. Soon after this the rainy season commences and continues till
the end of September, the beginning of this season occurs when a storm
from the Bay of Bengal passes over Bihar. The commencement of monsoon may be as
early as the last week of May or as the first or second week of July. The
climate in the cold weather is pleasant. The days are bright and warm and the
sun is not too hot. As soon as the sun sets the temperature falls and the heat of
the day yields place to a sharp bracing cold. The mean temperature in Gaya and
Patna in December is 17oC and 18.2oC
respectively.
The mean temperature in November
all over Bihar varies from 19.6oC in Ranchi to 22.2oC in
Jamshedpur. Over the plateau the average temperature is about 20oC though the minimum temperature is about 14oC.
The mean temperature in December at Ranchi and
Hazaribagh is 17oC. January is the coldest and cruelest month in Bihar.
The mean minimum
temperature varies from 7.5oC to 10.5oC though some
places like Netarhat record much lower temperatures than 7.5oC. In
the Chotanagpur plateau, December is the coldest month. The highest temperature is often registered in May which is the
hottest month in the state. Like the rest of the northern India, Bihar also experiences
dust-storms, thunder-storms and dust raising winds during the hot season. Dust
storms having a velocity of 48-64 Km/Hour are most frequent in May and with
second maximum in April and June. The hot winds (loo) of Bihar plains blow
during April and May with an average velocity of 8-16 Km/hour. This hot winds
greatly affects human comfort during this season. The rainy season begins in
June. The rainiest months are July and August. The rains are the gifts of the
south west monsoon. There are in Bihar three distinct areas where rainfall
exceeds 1800mm. Two of them lie on northern and north-western wings of the state
and the third lies in the Netarhat pat. The Chotanagpur highlands have a
better supply of rain than the adjoining northern and north-western plain
because of several reasons. They are nearer the source of monsoon depression
i.e. Bay and the delta. They are benefited by this supply both from the Bay and
the Arabian Sea branches. The south-west monsoon normally withdraws from Bihar in
the first week of October. An important feature of the retreating monsoon season
in Bihar is the invasion of tropical cyclones originating in the Bay of Bengal
at about 12oN latitude. Bihar is also influenced by the typhoons
originating in the south China sea. The maximum frequency of the tropical
cyclones in Bihar is during September-November especially during the asterism
called hathiya. These cyclones are essential for the maturing of paddy, and are
required for the moistening of the soil for the cultivation of rabi crops.
Rivers
One of the most striking feature of the river system of Bihar is
the dominant role of Ganga. The important rivers that join the Ganga from the
north are, from west to east, Ghaghra, the Gandak, the Burhi Gandak, the Kosi,
the Mahananda and its tributaries. Sonpur, which is situated along Ganga's bank
is famous for the great bathing festival which is the occasion for the greatest
cattle and elephant fair in the world. The Karmanasa, the Son , the Punpun, the
Phalgu, the Sakri and the Kiul are the principal streams that joins the Ganga
from the south. The principal rivers of Chotanagpur are the Damodar, the
Suvarnarekha, the Barakar and the Koel. The main dams Tilaiya,
Komar, Maithon and Panchet are all located in Bihar and also the thermal power
stations Bokaro and Patratu.
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