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Atmospheric River (AR) Event: In April 2025, the US experienced heavy rain, strong winds, and thunderstorms due to an AR, highlighting the increasing attention on this phenomenon due to climate change.
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Definition:
ARs are “rivers in the sky,” narrow bands transporting large amounts of water vapor from tropical oceans to continental regions. The “Pineapple Express” is a notable example. -
Characteristics: ARs can be up to 1,600 km long and 400-600 km wide, carrying water vapor equivalent to the Mississippi River’s flow, or up to 15 times more in stronger cases.
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Categorization: ARs are categorized from
Category 1 (weak, beneficial) to Category 5 (exceptional, hazardous), based on their impact, with higher categories causing significant flooding and destruction. -
Formation: ARs form from high evaporation over warm tropical oceans, guided by low-level jet streams toward mid-latitudes, condensing into rain or snow when forced upward by mountains or fronts.
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Global Impact: ARs are most common in mid-latitudes and responsible for over 90% of poleward water vapor transport.
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ARs and India: India experiences numerous AR events, mainly during the monsoon season, with ARs linked to major floods like those in Uttarakhand (2013) and Kerala (2018).
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Climate Change Impact: Rising temperatures increase atmospheric moisture, intensifying ARs and leading to longer, wider, and more extreme events, doubling the frequency of intense ARs. Warmer air can hold about 7% more moisture for each 1°C increase
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Hurricane-Like Conditions: ARs can cause hurricane-like conditions with intense rainfall, cyclone-force winds, and high waves.
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Increased intensity: While frequency may not increase, the intensity of ARs is expected to rise, leading to more severe flooding worldwide.
