The correct option is Humidity decreases as the winds get heated up..
Explanation
The phenomenon described is the Rain Shadow Effect associated with Orographic Rainfall. It involves the thermodynamic changes air undergoes as it ascends a mountain barrier and subsequently descends on the leeward side.
Detailed Analysis:
- Windward Side (Ascent): As moist winds strike the Western Ghats, they are forced to rise. Rising air expands and cools (adiabatic cooling), leading to condensation and heavy precipitation on the windward slopes. This process removes a significant amount of moisture from the air mass.
- Leeward Side (Descent): After crossing the crest, the winds descend the eastern slopes. Descending air undergoes adiabatic compression, which causes the temperature of the air to rise.
- Effect on Humidity:
- As the air warms up due to compression, its capacity to hold moisture increases.
- However, since the absolute moisture content was depleted during precipitation on the windward side, the Relative Humidity decreases sharply as the temperature rises.
- This results in the winds becoming dry and warm, creating semi-arid conditions in the rain shadow region.
Key Takeaway: Winds descending on the leeward side of a mountain undergo adiabatic warming. This increase in temperature, combined with prior moisture loss, causes a significant decrease in humidity.