• Recent Wayanad landslide and other catastrophic climate related incidents are raising concerns that ‘Rivers in the sky’ are becoming more intense in India, which could be linked with devastating floods, heat stress

Background

• A recent study by the Indian Institute of Tropical Meteorology (IITM) examined the role of ARs in the extreme rainfall events over the Indian subcontinent. 
• The study highlighted the need for improved forecasting models to predict AR impacts accurately, emphasizing their importance in the context of monsoon variability and climate change

What are Atmospheric Rivers?

• Atmospheric rivers (ARs) are invisible narrow corridors or filaments of concentrated moisture in the atmosphere. 
• They are typically 250-375 miles wide and can stretch for thousands of miles long. 
• These rivers in the sky transport large amounts of water vapor from the tropics to mid-latitude and polar regions, playing a crucial role in the global water cycle.

Characteristics or Features of Atmospheric Rivers

1. Narrow and Elongated: Typically 250-375 miles wide but can be thousands of miles long.
2. High Water Vapor Content: Can carry as much water vapor as the Amazon River does in liquid form.
3. Low-level Jet Stream: Often associated with strong low-level jets that transport moisture at high speeds.
4. Formation Over Oceans: Generally form over oceans and transport moisture to land.
5. Seasonal Occurrence: Most common in winter, though they can occur at any time of year.
6. Influenced by Large-scale Weather Patterns: Often interact with mid-latitude cyclones and other large-scale atmospheric phenomena.

Mechanism of Precipitation from Atmospheric Rivers

• Formation: ARs form when warm, moist air from the tropics is transported to higher latitudes by wind currents.
• Condensation: As the moist air moves over land and encounters mountains or colder air masses, it rises and cools, leading to condensation and cloud formation.
• Precipitation: The condensed moisture falls as precipitation, which can range from light rain to intense downpours, depending on the AR’s moisture content and the local atmospheric conditions.
• Orographic Lift: When ARs hit mountain ranges, the air is forced to rise, leading to significant precipitation on the windward side of the mountains.

Impact of Atmospheric Rivers in the World

Beneficial Effects:

1. Major source of water supply for regions like the west coast of the USA, particularly California.
2. Help in replenishing reservoirs and aquifers.

Adverse Effects:

1. Can cause severe flooding and landslides.
2. Associated with economic losses and infrastructure damage.
3. Can disrupt transportation and power supply.

Historical Events:

1. The 2019-2020 Australian bushfires were followed by AR-driven rains that helped extinguish fires but also caused floods.

Impact of Atmospheric Rivers in India with Examples

• 2018 Kerala Floods: ARs contributed significantly to the heavy rains that led to one of the worst floods in Kerala’s history.
• Northwest India: ARs have been linked to extreme rainfall events in northwest India, affecting states like Punjab and Haryana.
• Himalayan Region: ARs can cause heavy snowfall in the Himalayas, impacting river flows and potential flooding downstream during the melt season.

Impact of Global Warming on Atmospheric Rivers

• Increased Intensity and Frequency: Global warming is likely to intensify ARs due to higher moisture content in a warmer atmosphere.
• Shift in Patterns: Changes in global wind patterns may alter the paths and impacts of ARs.
• Enhanced Precipitation: Warmer temperatures can increase the potential for heavier precipitation events associated with ARs.

Advantages of Atmospheric Rivers

• Water Supply: Critical for water resources in drought-prone areas.
• Ecosystem Support: Provide necessary moisture for forests and other ecosystems.
• Agricultural Benefits: Can deliver much-needed rain for crops.