Geography: April 2025 UPSC Current Affairs | Geography for UPSC CSE PDF Download

Atmospheric River

Why in News?

In April 2025, the United States faced significant weather disturbances characterized by heavy rainfall, strong winds, and severe thunderstorms. These conditions were attributed to a meteorological phenomenon known as an Atmospheric River (AR). The increasing frequency of such events has drawn attention to the impact of climate change on weather patterns.

Key Takeaways

• An Atmospheric River is a long, narrow band in the atmosphere that transports large amounts of water vapor from tropical oceans to continental areas.
• The 'Pineapple Express' is a notable example of AR storms that primarily affect the US West Coast, especially California.

Additional Details

• Characteristics:
  • Shape & Size: ARs can extend up to 1,600 km in length and can vary from 400 to 600 km in width, as noted by the National Oceanic and Atmospheric Administration (NOAA).
  • Moisture Content: They can carry water vapor equivalent to the average flow of the Mississippi River, with the most intense ARs transporting up to 15 times more.
• Categories of Atmospheric Rivers:
  • Category 1 (Weak): Generally beneficial, aiding soil moisture and drought recovery.
  • Category 2 (Moderate): Benefits reservoirs but can lead to localized flooding if rain persists.
  • Category 3 (Strong): A mix of benefits and hazards; while it replenishes water supplies, it also poses flooding risks.
  • Category 4 (Extreme): Predominantly hazardous, capable of causing severe flooding but can assist in drought recovery.
  • Category 5 (Exceptional): Primarily hazardous, leading to catastrophic flooding and significant economic losses.
• Formation: ARs develop when warm ocean waters, particularly in tropical or subtropical regions, lead to high evaporation rates, which saturate the atmosphere with moisture. This moisture is then directed toward mid-latitudes by low-level jet streams and condenses into precipitation when it encounters mountains or fronts.
• Significance: Atmospheric Rivers play a crucial role in replenishing water supplies and contribute to over 90% of poleward water vapor transport in mid-latitudes. Their landfall can result in extreme precipitation.
• AR in India: Between 1951 and 2020, India recorded 596 major AR events, mostly during the summer monsoon. Significant floods, including the 2013 Uttarakhand floods and the 2018 Kerala floods, were linked to these events, which have become more frequent and severe in recent decades.
• Impact of Climate Change: Rising global temperatures are intensifying AR impacts. For every 1°C increase, air can hold approximately 7% more moisture, making storms fueled by ARs more potent. Future projections suggest that ARs will become longer, wider, and more intense, thereby doubling the occurrence of extreme AR events and heightening flood risks.

The increasing prevalence and intensity of Atmospheric Rivers underscore the need for enhanced understanding and preparedness against their potentially devastating impacts, particularly in vulnerable regions.