Key facts

  • The 50 cm isohyet broadly follows the Aravalli belt and separates the drier west from the wetter east and south-east.
  • Rajasthan's main rainy season is the south-west monsoon period from late June to September, when about 90% of useful rain is received.
  • Phalodi in Jodhpur district recorded 51.0°C on 19 May 2016, a high-yield station fact for extreme summer heat.

Key Points at a Glance

  1. 1

    The Aravalli range runs broadly south-west to north-east, nearly parallel to the Arabian Sea branch, so western Rajasthan remains in a rain-shadow setting.

  2. 2

    The 50 cm isohyet broadly follows the Aravalli belt and separates the drier west from the wetter east and south-east.

  3. 3

    Rajasthan's main rainy season is the south-west monsoon period from late June to September, when about 90% of useful rain is received.

  4. 4

    Phalodi in Jodhpur district recorded 51.0°C on 19 May 2016, a high-yield station fact for extreme summer heat.

  5. 5

    Mawat is winter rain from western disturbances and supports rabi crops such as wheat, mustard and gram.

  6. 6

    Koeppen zones in Rajasthan range from hot desert in the west to semi-arid steppe in the centre and more humid monsoon-influenced types towards the east and south-east.

  7. 7

    The State Action Plan on Climate Change links Rajasthan's drought, heat, rainfall variability, water, agriculture, forestry and biodiversity concerns.

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Aravalli Control And Rainfall Divide

Rajasthan's climate is first shaped by the Aravalli range. The range runs broadly from south-west to north-east, nearly parallel to the Arabian Sea branch of the south-west monsoon. Because the winds are not forced to rise strongly across most of the range, the western districts remain dry while the south and south-east receive more reliable monsoon rain. This rain-shadow pattern explains why Jaisalmer, Barmer and Bikaner are much drier than Udaipur, Banswara, Dungarpur, Kota and Jhalawar.

The 50 cm isohyet is a practical rainfall divide. West of it, annual rainfall commonly falls below 50 cm and agriculture faces drought, high evaporation and groundwater stress. East and south-east of it, rainfall of 50-100 cm or more supports better moisture, river basins, forest patches and denser vegetation. The divide is not a rigid wall, because dunes, rocky uplands, saline flats, distance from sea and local monsoon pulses all modify the pattern.

For objective exams, remember the link: Aravalli orientation controls monsoon lifting, rainfall gradient and Thar aridity.

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