The spatial patterns of rainfall and temperature are fundamental determinants in the delimitation of India's diverse climatic regions, profoundly influencing vegetation, agriculture, and human activities. India's climate is predominantly tropical monsoon, but its vast latitudinal and altitudinal extent, coupled with varied physiography, creates significant regional variations.

Rainfall is arguably the most critical factor. The monsoon system dictates distinct wet and dry seasons across the country. Regions like the Western Ghats, Northeast India, and the Himalayan foothills receive very high rainfall, supporting lush evergreen forests and intensive rice cultivation. In contrast, Rajasthan and parts of the Deccan Plateau receive scanty rainfall, leading to arid and semi-arid conditions, characterized by sparse vegetation and drought-resistant crops. Dudley Stamp's climatic regionalization prominently used the 75 cm (30 inches) annual isohyet as a crucial dividing line. He categorized India into 'Wet India' (east of the 75 cm isohyet), suitable for rice cultivation, and 'Dry India' (west of the 75 cm isohyet), where wheat and millets are more common. This simple yet effective division highlights the profound impact of rainfall on agricultural practices and regional character.

Temperature also plays a significant role. India's tropical location ensures high temperatures for most of the year in the plains, but altitude introduces variations. The Himalayas experience temperate to alpine climates with distinct cold winters, while the southern peninsular regions have more equable temperatures due to maritime influence. Stamp's classification, while emphasizing rainfall, implicitly incorporates temperature by recognizing the tropical nature of most of India and the distinct seasonal temperature regimes that influence crop cycles. For instance, the duration of the hot season and the presence or absence of frost are critical for specific crops. Together, the interplay of rainfall and temperature creates the mosaic of climatic regions that define India's geographical diversity.