Atmospheric rivers can produce heavy precipitation and associated hazards worldwide. A new study identifies regions where these hazards have already, and will further, increase with global heating.
By Thomas Stacker, EOS
Atmospheric rivers (ARs) are coherent current structures in the atmosphere that transport moisture and are important elements to deliver water through heavy precipitation events. They can also cause substantial hazards in many regions of the world. Due to their intrinsically long and narrow extent and high variability, it is challenging to observe and detect trends in AR activity and characteristics. Yet, this would be crucial for water resource planning and adaptation strategies.
Based on hourly atmospheric reanalysis data and applying several identification tools, Scholz and Lora [2025] find that the frequency of ARs in mid-latitudes of both hemispheres has robustly increased since 1940. Particularly, in the Southern Hemisphere, over the eastern United States, the North Atlantic region and into western Europe (see Figure), with concurrent increases in precipitation and snowfall. Less obvious surface impacts of ARs are warm winters and extreme heat events.
The longer-term context for AR trends that is established by the authors helps climate model simulations to better assess this important feature of atmospheric circulations and eventually improve projections. These are crucial inputs for decision makers to make water management and hazard prevention fit for the future. However, for example, formal detection and attribution studies on ARs are still challenging due to the large uncertainties associated with this fine-scale feature of atmospheric circulation.
RESEARCH PAPER: Widespread increase in atmospheric river frequency and impacts over the 20th century
By: Scholz, S. R., & Lora, J. M. (2025)
ABSTRACT: Atmospheric rivers (ARs) play a dominant role in water resource availability in many regions, and can cause substantial hazards, including extreme precipitation, flooding, and moist heatwaves. Despite this, there is substantial uncertainty about recent and ongoing changes in AR frequency and impacts. Here, we place recent observed trends in their longer-term context using AR records extending back to 1940. Our results show that AR frequency has increased broadly across the midlatitudes, bridging the apparent discrepancy between the observed satellite-era poleward shift and the general increase simulated in climate change projections. This increase in AR frequency enhances AR-associated precipitation and snowfall across their region of influence in the mid- and high-latitudes. We also find that, despite warmer surface temperatures associated with ARs, there is a decrease in the magnitude of AR-associated temperature anomalies in high-latitude regions due to Arctic amplification. An increase in AR-associated humid heatwaves underscores the societal importance of changing AR activity.
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