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Publication Date
28 June 2023

Global Warming Intensifies Rainfall Extremes in High-Elevation Regions

A shift from snow to rain in the Northern hemisphere mountains amplifies extreme rainfall.
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The Risk Ratio (RR) of extreme rainfall. An RR value of 2 means that an event is 2 times more likely to occur in a future climate. Regions in dark blue color (e.g., Pacific Mountain ranges, Rockies, Himalayas) have high risk of rainfall extremes in a future climate.

Global warming is expected to amplify extreme precipitation events, but the fractions of rain and snowfall during these events is poorly understood. This study focuses on changes to rainfall (liquid precipitation) extremes with warming due to its potential impact on flooding, landslides, and erosion. Our findings reveal a 15% intensity increase per 1 degree C of warming in mountainous regions — which is twice the previously observed rate for total extreme precipitation. Consequently, high-elevation regions (e.g., Sierra Nevada, Cascades, Rockies, Alps, Himalayas) become vulnerable hotspots for future rainfall extremes, amplifying risks like flooding, landslides, and soil erosion. This insight enhances our understanding of the impacts on specific regions and its associated hazards. 


These results will provide information for risk assessment of rainfall-related hazards like floods and landslides in vulnerable regions, home to a significant portion of the global population residing in mountains and their foothills. They provide valuable insights for developing effective adaptation and mitigation strategies, enabling us to incorporate projected increases in rainfall extremes into infrastructure design and natural resources management. Furthermore, the study identifies specific components within climate models requiring improvement to reduce uncertainty in projections of rainfall extremes.


In a warmer climate, the intensity of extreme precipitation events is expected to increase, posing significant challenges to water sustainability in natural and built environments. Particularly, the extremes of rainfall (liquid precipitation) are crucial due to their immediate impact on runoff, as well as their association with floods, landslides, and soil erosion. However, existing scientific studies on precipitation extremes have not distinguished between rainfall and snowfall. Our study addresses this gap and reveals that in high-elevation regions of the Northern Hemisphere, the increase in rainfall extremes is amplified by an average of 15% per degree Celsius of warming—twice the expected rate from atmospheric water vapor increases alone. We analyze both observations (climate reanalysis data) and future model projections, demonstrating that this amplified increase is already occurring and is caused due to a shift from snow to rain due to warming air temperatures. Moreover, we find that changes in the fractions of snow and rain explain a significant portion of the intermodel uncertainty in rainfall extremes projections (coefficient of determination 0.47). These findings highlight high-altitude regions as vulnerable "hotspots" facing future risks from extreme rainfall-related hazards, necessitating robust climate adaptation plans to mitigate potential dangers. Furthermore, our results provide a pathway for reducing model uncertainty in rainfall extremes projections.

Point of Contact
William D. Collins
Lawrence Berkeley National Laboratory
Funding Program Area(s)