The correct option is The winds blow parallel to the Aravalis and do not encounter a barrier..
Explanation
The distribution of rainfall in India is significantly influenced by the interaction between moisture-laden monsoon winds and the physiography (relief) of the land. Orographic rainfall occurs when mountain barriers obstruct wind flow, forcing the air to rise, cool, and condense.
Analysis of the Phenomenon:
- Orientation of the Aravalli Range: The Aravalli Range extends in a Southwest to Northeast direction across Rajasthan.
- Interaction with Monsoon Winds: The Arabian Sea branch of the Southwest Monsoon blows from the southwest towards the northeast. Consequently, the winds blow parallel to the alignment of the Aravalli mountains.
- Absence of Orographic Lift: Because the mountains do not act as a perpendicular barrier, they fail to obstruct the winds. The winds glide along the range without being forced to rise vertically. Without this uplift, the air does not cool sufficiently to cause condensation and precipitation.
Option Analysis:
- The winds are dry when they reach Rajasthan. is incorrect: The winds originating from the Arabian Sea carry moisture; they are not inherently dry. They remain moisture-laden but fail to precipitate due to the lack of a lifting mechanism.
- The winds blow parallel to the Aravalis and do not encounter a barrier. is correct: The parallel alignment of the Aravallis relative to the wind direction prevents the obstruction necessary for rainfall.
- The high temperature in Rajasthan evaporates the rain before it hits the ground. is incorrect: While high temperatures reduce relative humidity, the primary reason for the lack of rainfall is the absence of cloud formation mechanisms (uplift), not the evaporation of falling rain.
- The pressure conditions repel the monsoon winds. is incorrect: The intense low-pressure area over Northwest India (Rajasthan) actually attracts the monsoon winds rather than repelling them.
Key Takeaway:
Rajasthan receives scanty rainfall primarily because the Aravalli Range runs parallel to the direction of the Arabian Sea branch of the Southwest Monsoon, preventing the orographic lifting required for precipitation.