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Approach:

  1. Explain meaning of variability of rainfall and give a brief pattern of variability distribution in India.
  2. Elaborate on the phenomenon of monsoon breaks.

Variability : The variability of rainfall is defined as percentage change from the mean values of rainfall at a place. Variability is the major cause of floods and draughts in an area. Variation in rainfall may occur because of global (like El-Nino, IOD) or regional (like positioning of Jet Streams) or local (like areas where two monsoon branches meet) factors.

  • Variability < 25% – Western coasts, Western Ghats, Eastern plains of Ganga through North East, Northeast part of peninsula (Avg. Annual rainfall > 100 cm).
  • Variability > 50% – Western Rajasthan, Northern part of J&K, interior parts of the Deccan Plateau (Avg. annual rainfall < 50 cm).
  • Rest of India has a variability of 25-50% and these areas receive an annual rainfall of 50-100 cm.

Sudden Break: During South-West monsoon period after having rains for a few days, if rain fails to occur for one or two weeks, it is known as break in monsoon. These breaks in the different regions are due to different reasons-

  • In the northern India rains are likely to fail if the rain bearing storms are not very frequent along the monsoon trough.
  • ITCZ gets stuck on Himalayan foothills due to its interaction with the Sub-tropical jet. This causes breaks for several days over north India, while causing incessant rains in hills.
  • Over the West Coast, the dry spells are associated with days when winds blow parallel to the coast.
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