Why in the News?

Droughts and fires in South America highlight the importance of “flying rivers” — rain-bearing vapor streams disrupted by Amazon deforestation.

What are Atmospheric Rivers?

Overview: Long, narrow bands of concentrated water vapour in the lower atmosphere, often termed “rivers in the sky.”
Dimensions: Typically 2,000–5,000 km long, 400–500 km wide, and about 3 km deep.
Water Transport: Carry nearly 90% of water vapour across Earth’s mid-latitudes — almost double the Amazon River’s flow.
Formation: Warm tropical seawater evaporates, and winds transport this moisture; upon encountering land or mountains, vapour condenses into heavy rainfall or snow.
Role: Unlike short-term weather systems, Atmospheric Rivers (ARs) shape long-term hydrological cycles and trigger extreme precipitation events.

Flooding & Extreme Weather: Cause 80% of flood-related damages along the US West Coast; also linked to devastating floods in Europe, Africa, South America, and Australia.
South America: Amazon’s “flying rivers” disrupted by deforestation, leading to droughts in Peru, Bolivia, and Ecuador; threatens Amazon rainforest’s survival and risks savannisation.
East Asia: Up to 80% of heavy rainfall events in China, Korea, and Japan during early monsoon linked to ARs.
Climate Connection: Warming oceans are making ARs longer, wider, and more intense, increasing risks of catastrophic floods and landslides.
Positive Role: Contribute 30–50% of annual precipitation in some regions (e.g., US West Coast) and help end 33–74% of droughts.

Interaction: ARs combine with cyclonic circulations and the Himalayan ranges, causing extreme rainfall and flash floods.
Case Studies:
- 2010 Leh cloudburst (Ladakh) – flash floods and mudslides.
- 2011 Kupwara floods (J&K) – severe AR-driven rainfall.
Study (1951–2020): Identified 574 AR events during the monsoon season in India.
Recent Trends: Nearly 80% of India’s most severe floods (1985–2020) linked to AR activity.
Cause: Rapid Indian Ocean warming intensifies evaporation, moisture transport, and AR-driven floods.
Impact: Leads to short, intense rainfall spells, landslides, flash floods, crop loss, and mass displacement of communities.

[UPSC 2024] With reference to “water vapour,” which of the following statements is/are correct?

1. It is a gas, the amount of which decreases with altitude.

2. Its percentage is maximum at the poles.

Select the answer using the code given below:

Options: (a) 1 only* (b) 2 only (c) Both 1 and 2 (d) Neither 1 and 2