Page 169 - SST Class 06

rising from south to north. In March temper- The Arabian Sea Branch is controlled by
ature is around 38°C in the deccan Plateau,
as the heat belt moves north the tempera-
ture rises upto 42°C to 43°C in Gujarat and
Madhya Pradesh. During May, the day
temperature may be more than 45°C in
most north – western parts of India.
The high temperature causes formation of
low pressure belt in the north-west. It
becomes further intense due to shifting of
upper air currents towards north of
Himalaya. Dry and hot winds blow in the
afternoons. Locally known as loo, they
cause great hardships to people and result in
many deaths due to heat-stroke. Local
thunder-storms like Kalbaisakhi, calamity of
Baisakhi, are also common in west Bengal
and Assam.
Towards the end of summer season, pre-
monsoon showers are experienced in
Kerala. These showers are useful for ripen-
ing of mangoes and are, therefore, known
as ‘Mango Showers’.
3. Advance Monsoon Season (June to
September) : This season begins in June
4. Retreating Monsoon Season or Post
and lasts till the end of September. Almost
90 percent of the rainfall is received in this
season. The low-pressure belt in the north-
west becomes more intense. It attracts the
winds blowing over the Indian Ocean. The
trade winds that blow over the Indian
Ocean crosses the equator. They are
deflected by the earth’s rotation. These
strong moisture laden winds blow from
south-west to north-east and are, therefore,
known as South-West Monsoon. For most
parts, sky remains overcast with clouds. The
weather is generally oppressive with high
humidity. These winds reach India in two
branches— the Arabian Sea branch and the
Bay of Bengal branch.
Social Science-6 169
relief. It moves along the west coast and
reaches Kerala by the beginning of June.
There is abundant rainfall on the western
slopes of Western Ghats and the winds
move on further passing over western
Rajasthan along the Aravalli and reaches
western Himalaya without shedding any
moisture there.
The Bay of Bengal Branch strikes Andaman
and Nicobar Island and the eastern parts of
Himalaya, but is deflected westwards over
Ganga plains. The branch moving westward
causes rainfall in decreasing order – Kolkata
162 cm, Patna 116 cm, Allahabad 98 cm
and Delhi 66 cm. The upper air currents act
in tandem with the trade winds and take
their own time to create right conditions for
attracting south-west monsoon winds.
Therefore, there are breaks of dry spells
when the rains do not occur. When the
conditions are right, there is violent thunder
and lightning which is known as burst of
monsoon. Sometimes, rains fall for a few
days and cause floods.
Monsoon Season (October and Nov-
ember) : Retreat means an ‘orderly’ with-
drawal. The withdrawal of south-west
monsoons is truly orderly. The monsoons
begin withdrawing from the north-western
plains or Punjab by the last week of
September. They gradually start becoming
very weak. By the last week of October, the
monsoons also withdraw from West Bengal.
The S.W. Monsoon in this season holds
sway only in South India. South Indian states
of Andhra Pradesh, Tamil Nadu, Karnataka
and Kerala receives rainfall in this season.
The months of October and November are
marked by clear skies and rise in tem-