Introduction:
India is a vast country with diverse geographical features, and its climate is influenced by various factors such as latitude, altitude, topography, and the monsoon winds. The east-west variation in rainfall across India can be attributed to these factors.

Monsoon Winds:
The southwest monsoon, which brings the majority of rainfall to India, plays a crucial role in the east-west variation of rainfall. The monsoon winds blow from the southwest towards the northeast, bringing abundant moisture from the Indian Ocean. As these winds move inland, they encounter various geographical barriers, causing changes in their moisture content and resulting in varying precipitation patterns.

Arabian Sea Branch:
The Arabian Sea branch of the southwest monsoon first hits the western coast of India, bringing heavy rainfall to the coastal regions of the Western Ghats. These mountains act as a barrier, forcing the moisture-laden winds to ascend, cool, and condense, leading to significant precipitation on the windward side (western side) of the Western Ghats. As a result, states like Kerala, Karnataka, and Maharashtra receive ample rainfall.

Bay of Bengal Branch:
The Bay of Bengal branch of the southwest monsoon moves towards the northeastern states of India, crossing the Bay of Bengal. The Bay of Bengal is relatively warmer compared to the Arabian Sea, providing more moisture to the monsoon winds. The Himalayas act as a barrier, causing the winds to ascend and cool, resulting in heavy rainfall on the windward side (eastern side) of the mountain range. Consequently, states like Assam, Meghalaya, and West Bengal receive substantial precipitation.

Rain Shadow Effect:
The Western Ghats and the Himalayas also create a rain shadow effect, causing a decrease in rainfall on the leeward side (eastern side) of these mountain ranges. As the moisture-laden winds ascend and cool on the windward side, they release most of their moisture, resulting in lesser rainfall on the leeward side. This explains why regions like Tamil Nadu, Andhra Pradesh, Odisha, and Bihar experience relatively lower rainfall compared to the windward side.

Conclusion:
The east-west variation in rainfall across India can be attributed to factors like the monsoon winds, geographical barriers like the Western Ghats and the Himalayas, and the rain shadow effect. These factors interact to create distinct precipitation patterns, with the windward side of the Western Ghats and the Himalayas receiving more rainfall compared to the leeward side. Understanding these factors is crucial for analyzing and predicting rainfall patterns in different regions of India.