Previous Year Question

Rainfall is the process in which water droplets formed through the Condensation of atmospheric Water Vapour fall to the Earth's surface. Sufficient Atmospheric Moisture is necessary for precipitation. The amount of water vapour present in the air is referred to as Humidity. The availability of atmospheric moisture is a major determinant of the potential amount of rainfall, because it provides the water required for cloud formation and precipitation. However, high humidity alone does not necessarily produce rainfall.

During Rainfall Formation, moist air rises, expands, and generally cools. When its temperature reaches the Dew Point, water vapour condenses around Condensation Nuclei, such as microscopic dust and salt particles, forming tiny cloud droplets. These droplets may collide and combine to form larger droplets. When they become too heavy to remain suspended by upward air currents, they fall to the Earth's surface as rain. Sustained rainfall requires a continuous supply of moisture and favourable atmospheric conditions.

Air Pressure, Temperature, and the Water Cycle also influence precipitation, but their roles differ. In low-pressure regions, rising air supports cloud formation. Temperature affects the saturation water-vapour content of air and the conditions required for condensation. The Water Cycle includes evaporation, condensation, precipitation, and the subsequent collection of water. Therefore, actual rainfall amounts depend not only on moisture availability but also on atmospheric uplift, cooling, and cloud microphysical processes.

The Southwest Monsoon in India provides an important example of the relationship between atmospheric moisture and rainfall. Monsoon winds transport large quantities of water vapour from the Arabian Sea and the Bay of Bengal towards the Indian subcontinent. When these moisture-laden winds encounter mountain ranges such as the Western Ghats or the Himalayas, they rise, cool, and undergo condensation, producing Orographic Rainfall. Thus, sufficient moisture, atmospheric uplift, and geographical conditions collectively influence the spatial distribution and amount of rainfall.