What is Precipitation and its types?

Precipitation, the release of moisture resulting from water vapour condensation, manifests in various forms like rainfall, snowfall, sleet, hailstones, freezing rain, and virga. Different types of rainfall, such as conventional, orographic, and cyclonic, occur based on distinct atmospheric processes and geographical factors. Understanding the distribution and types of rainfall is essential for comprehending regional climates and their impact on ecosystems and human activities.

Types of Precipitation

• Each type of precipitation has unique characteristics and is influenced by specific atmospheric conditions, contributing to diverse weather phenomena across different regions of the world. 
• Rainfall: Precipitation in the form of liquid water.
• Snowfall: When the temperature is below freezing point, precipitation takes the form of fine snowflakes.
• Sleet:  Consists of frozen raindrops or refrozen melted snow-water; 
• • Occurs when there’s a layer of air with a temperature above freezing point overlying a sub-freezing layer near the ground.
• Hailstones: Formed when rainwater droplets solidify into small, rounded pieces of ice while passing through colder layers; 
  • Typically have multiple concentric layers of ice.
• Freezing Rain: Drizzles or light rains occurring below 0° C temperature and being frozen before reaching the ground.
• Virage: Raindrops evaporate before reaching Earth in dry air.

Enroll now for UPSC Online Course

Types of Rainfall

On the Basis of Origin: 

• Convectional Rainfall: Warm air rises due to convection currents, expands, cools down, and subsequently undergoes condensation, resulting in the formation of cumulus clouds & precipitation.
  • Prevalent during the summer or in the warmer hours of the day.  
  • Particularly common in equatorial regions and the inner regions of continents, especially in the northern hemisphere.
  • Heavy rainfall accompanied by thunder and lightning occurs, but it tends to be of shorter duration.

• Orographic Rainfall (Relief Rainfall): Occurs when a moisture-saturated air mass encounters a mountain and is compelled to rise.  
  • With ascendance, adiabatic expansion and cooling takes place resulting in condensation and precipitation. 
  • More rainfall towards windward slopes, while on the leeward side (rainshadow area), adiabatic heating (temperatures increase) takes place, allowing for greater moisture absorption and resulting in dry conditions without rain.
  • Area situated on the leeward side is known as the rain-shadow area.
• Cyclonic Rainfall: Widespread precipitation associated with weather fronts and cyclones;  includes tropical and extratropical cyclonic rain.

World Distribution of Rainfall

• Rainfall diminishes steadily from the equator towards the poles. 
• Equatorial regions receive consistent year-round rainfall. 
• Coastal areas receive more rainfall than inland regions. 
• Between latitudes 35° and 40° N and S, eastern coasts get heavier rainfall due to easterly winds, decreasing westward. Between 45° and 65° N and S, westerly winds bring rainfall first to western continental margins, decreasing eastward. 

Rainfall regions

• Heavy Rainfall (greater than 200 cm annually): equatorial region; coastal monsoon region; Windward side of coastal mountains.
• Moderate Rainfall (between 100 to 200 cm annually): Adjacent regions of very heavy rainfall areas; Coastal regions in the warm temperate region.
• Inadequate Rainfall (between 50 to 100 cm annually): Eastern part of the continents in temperate regions; Interior of continents in tropical regions.
• Low Rainfall (less than 50 cm annually): Rain shadow regions; Western part of continents in tropical regions.

Conclusion

• Precipitation is a vital component of the Earth’s water cycle, impacting ecosystems, agriculture, and human societies worldwide.
• The distribution of rainfall varies significantly across different regions, influencing local climates and environmental conditions. 
• Recognising the patterns and types of rainfall helps in managing water resources, mitigating natural disasters, and adapting to changing climatic conditions in diverse geographical settings.

DOWNLOAD PDF