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Rainfall map for the foothills
(Source:
UNESCO
1984)
A major part of this
region falls in a zone of moderate to high rainfall (1200-2000mm annually),
higher towards the northeast due to proximity of the Himalayas. The
foothills above the plains of north Bihar experience a higher rainfall
(>2000 mm annually) that the plains. The climate is drier in high mountains
which are covered by snow most of the year.
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Rainfall map for the plains
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Daily
rainfall
(Source:
IMD) |
Monthly rainfall
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The
region experiences monsoonal rainfall, preceded by pre-monsoon showers. The
main monsoon usually arrives in mid-June in the plains of north Bihar, with
a sudden rise of humidity to over 70% and a sudden fall in temperature by
5-8 °C.
The season of rains, which provided over 85% of the annual rainfall, ceases
in September. The daily rainfall plot for one of the stations (Muzaffarpur)
illustrates the typical monsoonal rainfall. The total annual rainfall is
very strongly concentrated in the rainy season, and that amount is even more
concentrated in a few intensive rain hours during the 5-60 rainy days. Most
of the rain therefore drains off quickly without infiltrating the soil,
adding to the flashiness of channel discharge.
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